|
Network Working Group Request for Comments: 4765 Category: Experimental |
H. Debar France Telecom D. Curry Guardian B. Feinstein SecureWorks, Inc. March 2007 |
This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.
Copyright © The IETF Trust (2007).
The content of this RFC was at one time considered by the IETF, but the working group concluded before this work was approved as a standards-track protocol. This RFC is not a candidate for any level of Internet Standard. The IETF disclaims any knowledge of the fitness of this RFC for any purpose and in particular notes that the decision to publish is not based on complete IETF review for such things as security, congestion control, or inappropriate interaction with deployed protocols. The IESG has chosen to publish this document in order to document the work as it was when the working group concluded and to encourage experimentation and development of the technology. Readers of this RFC should exercise caution in evaluating its value for implementation and deployment.
The purpose of the Intrusion Detection Message Exchange Format (IDMEF) is to define data formats and exchange procedures for sharing information of interest to intrusion detection and response systems and to the management systems that may need to interact with them.
This document describes a data model to represent information exported by intrusion detection systems and explains the rationale for using this model. An implementation of the data model in the Extensible Markup Language (XML) is presented, an XML Document Type Definition is developed, and examples are provided.
1. Introduction
1.1. About the IDMEF Data Model
1.1.1. Problems Addressed by the Data Model
1.1.2. Data Model Design Goals
1.2. About the IDMEF XML Implementation
1.2.1. The Extensible Markup Language
1.2.2. Rationale for Implementing IDMEF in XML
2. Notices and Conventions Used in This Document
3. Notational Conventions and Formatting Issues
3.1. IDMEF XML Documents
3.1.1. The Document Prolog
3.1.2. Character Data Processing in IDMEF
3.1.3. Languages in IDMEF
3.2. IDMEF Data Types
3.2.1. Integers
3.2.2. Real Numbers
3.2.3. Characters and Strings
3.2.4. Bytes
3.2.5. Enumerated Types
3.2.6. Date-Time Strings
3.2.7. NTP Timestamps
3.2.8. Port Lists
3.2.9. Unique Identifiers
4. The IDMEF Data Model and DTD
4.1. Data Model Overview
4.2. The Message Classes
4.2.1. The IDMEF-Message Class
4.2.2. The Alert Class
4.2.3. The Heartbeat Class
4.2.4. The Core Classes
4.2.5. The Time Classes
4.2.6. The Assessment Classes
4.2.7. The Support Classes
5. Extending the IDMEF
5.1. Extending the Data Model
5.2. Extending the IDMEF DTD
6. Special Considerations
6.1. XML Validity and Well-Formedness
6.2. Unrecognized XML Tags
6.3. Analyzer-Manager Time Synchronization
6.4. NTP Timestamp Wrap-Around
6.5. Digital Signatures
7. Examples
7.1. Denial-of-Service Attacks
7.1.1. The "teardrop" Attack
7.1.2. The "ping of death" Attack
7.2. Port Scanning Attacks
7.2.1. Connection to a Disallowed Service
7.2.2. Simple Port Scanning
7.3. Local Attacks
7.3.1. The "loadmodule" Attack
7.3.2. The "phf" Attack
7.3.3. File Modification
7.4. System Policy Violation
7.5. Correlated Alerts
7.6. Analyzer Assessments
7.7. Heartbeat
7.8. XML Extension
8. The IDMEF Document Type Definition (Normative)
9. Security Considerations
10. IANA Considerations
10.1. Adding Values to Existing Attributes
10.1.1. Attribute Registrations
10.1.2. Registration Template
10.2. Adding New Attributes and Classes
11. References
11.1. Normative References
11.2. Informative References
Appendix A. Acknowledgements
Appendix B. The IDMEF Schema Definition (Non-normative)
The Intrusion Detection Message Exchange Format (IDMEF) [2] is intended to be a standard data format that automated intrusion detection systems can use to report alerts about events that they deem suspicious. The development of this standard format will enable interoperability among commercial, open source, and research systems, allowing users to mix-and-match the deployment of these systems according to their strong and weak points to obtain an optimal implementation.
The most obvious place to implement the IDMEF is in the data channel between an intrusion detection analyzer (or "sensor") and the manager (or "console") to which it sends alarms. But there are other places where the IDMEF can be useful:
The diversity of uses for the IDMEF needs to be considered when selecting its method of implementation.
The IDMEF data model is an object-oriented representation of the alert data sent to intrusion detection managers by intrusion detection analyzers.
The data model addresses several problems associated with representing intrusion detection alert data:
An object-oriented model is naturally extensible via aggregation and subclassing. If an implementation of the data model extends it with new classes, either by aggregation or subclassing, an implementation that does not understand these extensions will still be able to understand the subset of information that is defined by the data model. Subclassing and aggregation provide extensibility while preserving the consistency of the model.
The data model defines support classes that accommodate the differences in data sources among analyzers. In particular, the notions of source and target for the alert are represented by the combination of Node, Process, Service, and User classes.
The data model defines extensions to the basic Document Type Definition (DTD) that allow carrying both simple and complex alerts. Extensions are accomplished through subclassing or association of new classes.
Significant flexibility in reporting is provided by the Node and Service support classes. If additional information must be reported, subclasses may be defined that extend the data model with additional attributes.
The object-oriented approach allows this flexibility while the subclassing rules preserve the integrity of the model.
The data model was designed to provide a standard representation of alerts in an unambiguous fashion, and to permit the relationship between simple and complex alerts to be described.
The goal of the data model is to provide a standard representation of the information that an intrusion detection analyzer reports when it detects an occurrence of some unusual event(s). These alerts may be simple or complex, depending on the capabilities of the analyzer that creates them.
The design of the data model is content-driven. This means that new objects are introduced to accommodate additional content, not semantic differences between alerts. This is an important goal, as the task of classifying and naming computer vulnerabilities is both extremely difficult and very subjective.
The data model must be unambiguous. This means that while we allow analyzers to be more or less precise than one another (i.e., one analyzer may report more information about an event than another), we do not allow them to produce contradictory information in two alerts describing the same event (i.e., the common subset of information reported by both analyzers must be identical and inserted in the same placeholders within the alert data structure). Of course, it is always possible to insert all "interesting" information about an
event in extension fields of the alert instead of in the fields where it belongs; however, such practice reduces interoperability and should be avoided whenever possible.
Intrusion detection alerts can be transmitted at several levels. This document applies to the entire range, from very simple alerts (e.g., those alerts that are the result of a single action or operation in the system, such as a failed login report) to very complex ones (e.g., the aggregation of several events causing an alert to be generated).
As such, the data model must provide a way for complex alerts that aggregate several simple alerts to identify those simple alerts in the complex alert's content.
Two implementations of the IDMEF were originally proposed to the Intrusion Detection Working Group (IDWG): one using the Structure of Management Information (SMI) to describe a Simple Network Management Protocol (SNMP) MIB, and the other using a DTD to describe XML documents.
These proposed implementations were reviewed by the IDWG at its September 1999 and February 2000 meetings; it was decided at the February meeting that the XML solution was best at fulfilling the IDWG requirements.
The Extensible Markup Language (XML) [3] is a simplified version of the Standard Generalized Markup Language (SGML), a syntax for specifying text markup defined by the ISO 8879 standard. XML is gaining widespread attention as a language for representing and exchanging documents and data on the Internet, and as the solution to most of the problems inherent in HyperText Markup Language (HTML). XML was published as a recommendation by the World Wide Web Consortium (W3C) on February 10, 1998.
XML is a metalanguage -- a language for describing other languages -- that enables an application to define its own markup. XML allows the definition of customized markup languages for different types of documents and different applications. This differs from HTML, in which there is a fixed set of identifiers with preset meanings that must be "adapted" for specialized uses. Both XML and HTML use elements (tags) (identifiers delimited by '<' and '>') and attributes
(of the form "name='value'"). But where "<p>" always means "paragraph" in HTML, it may mean "paragraph", "person", "price", or "platypus" in XML, or it might have no meaning at all, depending on the particular application.
NOTE: XML provides both a syntax for declaring document markup and structure (i.e., defining elements and attributes, specifying the order in which they appear, and so on) and a syntax for using that markup in documents. Because markup declarations look radically different from markup, many people are confused as to which syntax is called XML. The answer is that they both are, because they are actually both part of the same language.
For clarity in this document, we will use the terms "XML" and "XML documents" when speaking in the general case, and the term "IDMEF markup" when speaking specifically of the elements (tags) and attributes that describe IDMEF messages.
The publication of XML was followed by the publication of a second recommendation [4] by the World Wide Web Consortium, defining the use of namespaces in XML documents. An XML namespace is a collection of names, identified by a Uniform Resource Identifier (URI) [5]. When using namespaces, each tag is identified with the namespace it comes from, allowing tags from different namespaces with the same names to occur in the same document. For example, a single document could contain both "usa:football" and "europe:football" tags, each with different meanings.
In anticipation of the widespread use of XML namespaces, this memo includes the definition of the URI to be used to identify the IDMEF namespace.
XML-based applications are being used or developed for a wide variety of purposes, including electronic data interchange in a variety of fields, financial data interchange, electronic business cards, calendar and scheduling, enterprise software distribution, web "push" technology, and markup languages for chemistry, mathematics, music, molecular dynamics, astronomy, book and periodical publishing, web publishing, weather observations, real estate transactions, and many others.
XML's flexibility makes it a good choice for these applications; that same flexibility makes it a good choice for implementing the IDMEF as well. Other, more specific reasons for choosing XML to implement the IDMEF are:
XML also provides support for specifying, on a per-element basis, the language in which the element's content is written, making IDMEF easy to adapt to "Natural Language Support" versions of a product.
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [1].
An "IDMEF-compliant application" is a program or program component, such as an analyzer or manager, that reads and/or writes messages in the format specified by this memo.
An "IDMEF document" is a message that adheres to the requirements specified by this memo and that is exchanged by two or more IDMEF applications. "IDMEF message" is another term for an "IDMEF document".
This document uses three notations: Unified Modeling Language to describe the data model [14], XML to describe the markup used in IDMEF documents, and IDMEF markup to represent the documents themselves.
This section describes IDMEF XML document formatting rules. Most of these rules are "inherited" from the rules for formatting XML documents.
The format of an IDMEF XML document prolog is described in the following sections.
IDMEF documents being exchanged between IDMEF-compliant applications MUST begin with an XML declaration, and MUST specify the XML version in use. Specification of the encoding in use is RECOMMENDED.
An IDMEF message SHOULD therefore start with:
<?xml version="1.0" encoding="UTF-8"?>
<idmef:IDMEF-Message version="1.0"
xmlns:idmef="http://iana.org/idmef"/>
IDMEF-compliant applications MAY choose to omit the XML declaration internally to conserve space, adding it only when the message is sent to another destination (e.g., a web browser). This practice is NOT RECOMMENDED unless it can be accomplished without loss of each message's version and encoding information.
In order to be valid (see Section 6.1), an XML document must contain a document type definition. However, this represents significant overhead to an IDMEF-compliant application, both in the bandwidth it consumes as well as the requirements it places on the XML processor (not only to parse the declaration itself, but also to parse the DTD it references).
Implementors MAY decide, therefore, to have analyzers and managers agree out-of-band on the particular document type definition they will be using to exchange messages (the standard one as defined here, or one with extensions), and then omit the document type definition from IDMEF messages. The method for negotiating this agreement is outside the scope of this document. Note that great care must be taken in negotiating any such agreements, as the manager may have to accept messages from many different analyzers, each using a DTD with a different set of extensions.
For portability reasons, IDMEF-compliant applications SHOULD NOT use, and IDMEF messages SHOULD NOT be encoded in, character encodings other than UTF-8 and UTF-16. Consistent with the XML standard, if no encoding is specified for an IDMEF message, UTF-8 is assumed.
NOTE: The ASCII character set is a subset of the UTF-8 encoding, and therefore may be used to encode IDMEF messages.
Per the XML standard, IDMEF documents encoded in UTF-16 MUST begin with the Byte Order Mark described by ISO/IEC 10646 Annex E and Unicode Appendix B (the "ZERO WIDTH NO-BREAK SPACE" character,
#xFEFF).
It is RECOMMENDED that IDMEF-compliant applications use the entity reference form (see Section 3.2.3.1) of the characters '&', ,'<', '>', '"', and ''' (single-quote) whenever writing these characters in data, to avoid any possibility of misinterpretation.
All IDMEF elements MUST support the "xml:space" attribute.
IDMEF-compliant applications MUST specify the language in which their contents are encoded; in general this can be done by specifying the "xml:lang" attribute for the top-level element and letting all other elements "inherit" that definition [10].
Within an XML IDMEF message, all data will be expressed as "text" (as opposed to "binary"), since XML is a text formatting language. We provide typing information for the attributes of the classes in the data model, however, to convey to the reader the type of data that the model expects for each attribute.
Each data type in the model has specific formatting requirements in an XML IDMEF message; these requirements are set forth in this section.
Integer attributes are represented by the INTEGER data type. Integer data MUST be encoded in Base 10 or Base 16.
Base 10 integer encoding uses the digits '0' through '9' and an optional sign ('+' or '-'). For example, "123", "-456".
Base 16 integer encoding uses the digits '0' through '9' and 'a' through 'f' (or their uppercase equivalents), and is preceded by the characters "0x". For example, "0x1a2b".
Real (floating-point) attributes are represented by the REAL data type. Real data MUST be encoded in Base 10.
Real encoding is that of the POSIX 1003.1 "strtod" library function: an optional sign ('+' or '-') followed by a non-empty string of decimal digits, optionally containing a radix character, then an optional exponent part. An exponent part consists of an 'e' or 'E', followed by an optional sign, followed by one or more decimal digits. For example, "123.45e02", "-567,89e-03".
IDMEF-compliant applications MUST support both the '.' and ',' radix characters.
Single-character attributes are represented by the CHARACTER data type. Multi-character attributes of known length are represented by the STRING data type.
Character and string data have no special formatting requirements, other than the need to occasionally use character references (see Section 3.2.3.1 and Section 3.2.3.2) to represent special characters.
Within XML documents, certain characters have special meanings in some contexts. To include the actual character itself in one of these contexts, a special escape sequence, called an entity reference, must be used.
The characters that sometimes need to be escaped, and their entity references, are:
+-----------+------------------+
| Character | Entity Reference |
+-----------+------------------+
| & | & |
| | |
| < | < |
| | |
| > | > |
| | |
| " | " |
| | |
| ' | ' |
+-----------+------------------+
Any character defined by the ISO/IEC 10646 and Unicode standards may be included in an XML document by the use of a character reference. A character reference is started with the characters '&' and '#', and ended with the character ';'. Between these characters, the character code for the character is inserted.
If the character code is preceded by an 'x' it is interpreted in hexadecimal (base 16); otherwise, it is interpreted in decimal (base 10). For instance, the ampersand (&) is encoded as & or & and the less-than sign (<) is encoded as < or <.
Any one-, two-, or four-byte character specified in the ISO/IEC 10646 and Unicode standards can be included in a document using this technique.
Binary data is represented by the BYTE (and BYTE[]) data type.
Binary data MUST be encoded in its entirety using base64.
Enumerated types are represented by the ENUM data type, and consist of an ordered list of acceptable values.
Date-time strings are represented by the DATETIME data type. Each date-time string identifies a particular instant in time; ranges are not supported.
Date-time strings are formatted according to a subset of ISO 8601: 2000 [6], as show below. Section references in parentheses refer to sections of the ISO 8601:2000 standard [6].
YYYY-MM-DD
where YYYY is the four-digit year, MM is the two-digit month (01-12), and DD is the two-digit day (01-31). (Section 5.2.1.1, "Complete representation -- Extended format".)
hh:mm:ss
where hh is the two-digit hour (00-24), mm is the two-digit minute (00-59), and ss is the two-digit second (00-60). (Section 5.3.1.1, "Complete representation -- Extended format".)
Note that midnight has two representations, 00:00:00 and 24:00:00. Both representations MUST be supported by IDMEF- compliant applications; however, the 00:00:00 representation SHOULD be used whenever possible.
Note also that this format accounts for leap seconds. Positive leap seconds are inserted between 23:59:59Z and 24:00:00Z and are represented as 23:59:60Z. Negative leap seconds are achieved by the omission of 23:59:59Z. IDMEF-compliant applications MUST support leap seconds.
hh:mm:ss.ss or
hh:mm:ss,ss
As many digits as necessary may follow the decimal sign (at least one digit must follow the decimal sign). Decimal fractions of hours and minutes are not supported. (Section 5.3.1.3, "Representation of decimal fractions".)
IDMEF-compliant applications MUST support the use of both decimal signs ('.' and ',').
Note that the number of digits in the fraction part does not imply anything about accuracy -- i.e., "00.100000", "00,1000", and "00.1" are all equivalent.
hh:mm:ssZ
hh:mm:ss.ssZ
hh:mm:ss,ssZ
(Section 5.3.3, "Coordinated Universal Time (UTC) -- Extended format".)
hh:mm:ss+hh:mm
hh:mm:ss-hh:mm
hh:mm:ss.ss+hh:mm
hh:mm:ss.ss-hh:mm
hh:mm:ss,ss+hh:mm
hh:mm:ss,ss-hh:mm
The difference from UTC MUST be specified in both hours and minutes, even if the minutes component is 0. A "difference" of "+00:00" is equivalent to UTC. (Section 5.3.4.2, "Local time and the difference with Coordinated Universal Time -- Extended Format".)
YYYY-MM-DDThh:mm:ssZ
YYYY-MM-DDThh:mm:ss.ssZ
YYYY-MM-DDThh:mm:ss,ssZ
YYYY-MM-DDThh:mm:ss+hh:mm
YYYY-MM-DDThh:mm:ss-hh:mm
YYYY-MM-DDThh:mm:ss.ss+hh:mm
YYYY-MM-DDThh:mm:ss.ss-hh:mm
YYYY-MM-DDThh:mm:ss,ss+hh:mm
YYYY-MM-DDThh:mm:ss,ss-hh:mm
(Section 5.4.1, "Complete representation -- Extended format".)
In summary, IDMEF date-time strings MUST adhere to one of the nine templates identified in Paragraph 5, above.
NTP timestamps are represented by the NTPSTAMP data type and are described in detail in [7] and [8]. An NTP timestamp is a 64-bit unsigned fixed-point number. The integer part is in the first 32 bits, and the fraction part is in the last 32 bits.
Within IDMEF messages, NTP timestamps MUST be encoded as two 32-bit hexadecimal values, separated by a period ('.'). For example, "0x12345678.0x87654321".
See also Section 6.4 for more information on NTP timestamps.
Port lists are represented by the PORTLIST data type and consist of a
comma-separated list of numbers (individual integers) and ranges (N-M
means ports N through M, inclusive). Any combination of numbers and
ranges may be used in a single list. For example,
"5-25,37,42,43,53,69-119,123-514".
There are two types of unique identifiers used in this specification. Both types are represented by STRING data types.
These identifiers are implemented as attributes on the relevant XML elements, and they must have unique values as follows:
The "analyzerid" attribute is not required to be globally unique, only unique within the intrusion detection environment of which the analyzer is a member. It is permissible for two analyzers, in different intrusion detection environments, to have the same value for "analyzerid".
The default value is "0", which indicates that the analyzer cannot generate unique identifiers.
The "ident" attribute value MUST be unique for each particular combination of data identifying an object, not for each object. Objects may have more than one "ident" value associated with them. For example, an identification of a host by name would have one value, while an identification of that host by address would have another value, and an identification of that host by both name and address would have still another value. Furthermore, different analyzers may produce different values for the same information.
The "ident" attribute by itself provides a unique identifier only among all the "ident" values sent by a particular analyzer. But when combined with the "analyzerid" value for the analyzer, a value that is unique across the intrusion detection environment is created. Again, there is no requirement for global uniqueness.
The default value is "0", which indicates that the analyzer cannot generate unique identifiers.
The specification of methods for creating the unique values contained in these attributes is outside the scope of this document.
In this section, the individual components of the IDMEF data model are explained in detail. Unified Modeling Language (UML) diagrams of the model are provided to show how the components are related to each other, and relevant sections of the IDMEF DTD are presented to show how the model is translated into XML.
The relationship between the principal components of the data model is shown in Figure 1 (occurrence indicators and attributes are omitted).
The top-level class for all IDMEF messages is IDMEF-Message; each type of message is a subclass of this top-level class. There are presently two types of messages defined: Alerts and Heartbeats. Within each message, subclasses of the message class are used to provide the detailed information carried in the message.
It is important to note that the data model does not specify how an alert should be classified or identified. For example, a port scan may be identified by one analyzer as a single attack against multiple targets, while another analyzer might identify it as multiple attacks from a single source. However, once an analyzer has determined the type of alert it plans to send, the data model dictates how that alert should be formatted.
IDMEF-Message
/_\
|
+--------------------+-------------+
| |
+-------+ +--------------+ +-----------+ +----------------+
| Alert |<>-| Analyzer | | Heartbeat |<>-| Analyzer |
+-------+ +--------------+ +-----------+ +----------------+
| | +--------------+ | | +----------------+
| |<>-| CreateTime | | |<>-| CreateTime |
| | +--------------+ | | +----------------+
| | +--------------+ | | +----------------+
| |<>-| DetectTime | | |<>-| AdditionalData |
| | +--------------+ +-----------+ +----------------+
| | +--------------+
| |<>-| AnalyzerTime |
| | +--------------+
| | +--------+ +----------+
| |<>-| Source |<>-| Node |
| | +--------+ +----------+
| | | | +----------+
| | | |<>-| User |
| | | | +----------+
| | | | +----------+
| | | |<>-| Process |
| | | | +----------+
| | | | +----------+
| | | |<>-| Service |
| | +--------+ +----------+
| | +--------+ +----------+
| |<>-| Target |<>-| Node |
| | +--------+ +----------+
| | | | +----------+
| | | |<>-| User |
| | | | +----------+
| | | | +----------+
| | | |<>-| Process |
| | | | +----------+
| | | | +----------+
| | | |<>-| Service | +----------------+
| | | | +----------+ +----| Classification |
| | | | +----------+ | +----------------+
| | | |<>-| File | | +----------------+
| | +--------+ +----------+ | +--| Assessment |
| |<>----------------------------+ | +----------------+
| |<>------------------------------+ +----------------+
| |<>---------------------------------| AdditionalData |
+-------+ +----------------+
Figure 1: Data Model Overview
The individual classes are described in the following sections.
All IDMEF messages are instances of the IDMEF-Message class; it is the top-level class of the IDMEF data model, as well as the IDMEF DTD. There are currently two types (subclasses) of IDMEF-Message: Alert and Heartbeat.
The IDMEF-Message class has a single attribute:
version
The version of the IDMEF-Message specification (this document) this message conforms to. Applications specifying a value for this attribute MUST specify the value "1.0".
Generally, every time an analyzer detects an event that it has been configured to look for, it sends an Alert message to its manager(s). Depending on the analyzer, an Alert message may correspond to a single detected event or multiple detected events. Alerts occur asynchronously in response to outside events.
An Alert message is composed of several aggregate classes, as shown in Figure 2. The aggregate classes themselves are described in Section 4.2.4, Section 4.2.5, and Section 4.2.6.
+-------------------+
| Alert |
+-------------------+ +------------------+
| STRING messageid |<>----------| Analyzer |
| | +------------------+
| | +------------------+
| |<>----------| CreateTime |
| | +------------------+
| | +------------------+
| |<>----------| Classification |
| | +------------------+
| | 0..1 +------------------+
| |<>----------| DetectTime |
| | +------------------+
| | 0..1 +------------------+
| |<>----------| AnalyzerTime |
| | +------------------+
| | 0..* +------------------+
| |<>----------| Source |
| | +------------------+
| | 0..* +------------------+
| |<>----------| Target |
| | +------------------+
| | 0..1 +------------------+
| |<>----------| Assessment |
| | +------------------+
| | 0..* +------------------+
| |<>----------| AdditionalData |
| | +------------------+
+-------------------+
/_\
|
+----+------------+-------------+
| | |
+-------------------+ | +-------------------+
| ToolAlert | | | CorrelationAlert |
+-------------------+ | +-------------------+
|
+-------------------+
| OverflowAlert |
+-------------------+
Figure 2: The Alert Class
The aggregate classes that make up Alert are:
Analyzer
Exactly one. Identification information for the analyzer that originated the alert.
CreateTime
Exactly one. The time the alert was created. Of the three times that may be provided with an Alert, this is the only one that is required.
Classification
Exactly one. The "name" of the alert, or other information allowing the manager to determine what it is.
DetectTime
Zero or one. The time the event(s) leading up to the alert was detected. In the case of more than one event, the time the first event was detected. In some circumstances, this may not be the same value as CreateTime.
AnalyzerTime
Zero or one. The current time on the analyzer (see Section 6.3).
Source
Zero or more. The source(s) of the event(s) leading up to the alert.
Target
Zero or more. The target(s) of the event(s) leading up to the alert.
Assessment
Zero or one. Information about the impact of the event, actions taken by the analyzer in response to it, and the analyzer's confidence in its evaluation.
AdditionalData
Zero or more. Information included by the analyzer that does not fit into the data model. This may be an atomic piece of data, or a large amount of data provided through an extension to the IDMEF (see Section 5).
Alert is represented in the IDMEF DTD as follows:
<!ELEMENT Alert (
Analyzer, CreateTime, DetectTime?, AnalyzerTime?,
Source*, Target*, Classification, Assessment?, (ToolAlert |
OverflowAlert | CorrelationAlert)?, AdditionalData*
)>
<!ATTLIST Alert
messageid CDATA '0'
%attlist.global;
>
The Alert class has one attribute:
messageid
Optional. A unique identifier for the alert; see Section 3.2.9.
The ToolAlert class carries additional information related to the use of attack tools or malevolent programs such as Trojan horses and can be used by the analyzer when it is able to identify these tools. It is intended to group one or more previously-sent alerts together, to say "these alerts were all the result of someone using this tool".
The ToolAlert class is composed of three aggregate classes, as shown in Figure 3.
+------------------+
| Alert |
+------------------+
/_\
|
+------------------+
| ToolAlert |
+------------------+ +-------------------+
| |<>----------| name |
| | +-------------------+
| | 0..1 +-------------------+
| |<>----------| command |
| | +-------------------+
| | 1..* +-------------------+
| |<>----------| alertident |
| | +-------------------+
| | | STRING analyzerid |
| | +-------------------+
+------------------+
Figure 3: The ToolAlert Class
The aggregate classes that make up ToolAlert are:
name
Exactly one. STRING. The reason for grouping the alerts together, for example, the name of a particular tool.
command
Zero or one. STRING. The command or operation that the tool was asked to perform, for example, a BackOrifice ping.
alertident
One or more. STRING. The list of alert identifiers that are related to this alert. Because alert identifiers are only unique across the alerts sent by a single analyzer, the optional "analyzerid" attribute of "alertident" should be used to identify the analyzer that a particular alert came from. If the "analyzerid" is not provided, the alert is assumed to have come from the same analyzer that is sending the ToolAlert.
This is represented in the IDMEF DTD as follows:
<!ELEMENT ToolAlert (
name, command?, alertident+
)>
<!ATTLIST ToolAlert
%attlist.global;
>
The CorrelationAlert class carries additional information related to the correlation of alert information. It is intended to group one or more previously-sent alerts together, to say "these alerts are all related".
The CorrelationAlert class is composed of two aggregate classes, as shown in Figure 4.
+------------------+
| Alert |
+------------------+
/_\
|
+------------------+
| CorrelationAlert |
+------------------+ +-------------------+
| |<>----------| name |
| | +-------------------+
| | 1..* +-------------------+
| |<>----------| alertident |
| | +-------------------+
| | | STRING analyzerid |
| | +-------------------+
+------------------+
Figure 4: The CorrelationAlert Class
The aggregate classes that make up CorrelationAlert are:
name
Exactly one. STRING. The reason for grouping the alerts together, for example, a particular correlation method.
alertident
One or more. STRING. The list of alert identifiers that are related to this alert. Because alert identifiers are only unique across the alerts sent by a single analyzer, the optional "analyzerid" attribute of "alertident" should be used to identify the analyzer that a particular alert came from. If the "analyzerid" is not provided, the alert is assumed to have come from the same analyzer that is sending the CorrelationAlert.
This is represented in the IDMEF DTD as follows.
<!ELEMENT CorrelationAlert (
name, alertident+
)>
<!ATTLIST CorrelationAlert
%attlist.global;
>
The OverflowAlert carries additional information related to buffer overflow attacks. It is intended to enable an analyzer to provide the details of the overflow attack itself.
The OverflowAlert class is composed of three aggregate classes, as shown in Figure 5.
+------------------+
| Alert |
+------------------+
/_\
|
+------------------+
| OverflowAlert |
+------------------+ +---------+
| |<>----------| program |
| | +---------+
| | 0..1 +---------+
| |<>----------| size |
| | +---------+
| | 0..1 +---------+
| |<>----------| buffer |
| | +---------+
+------------------+
Figure 5: The OverflowAlert Class
The aggregate classes that make up OverflowAlert are:
program
Exactly one. STRING. The program that the overflow attack attempted to run (NOTE: this is not the program that was attacked).
size
Zero or one. INTEGER. The size, in bytes, of the overflow (i.e., the number of bytes the attacker sent).
buffer
Zero or one. BYTE[]. Some or all of the overflow data itself (dependent on how much the analyzer can capture).
This is represented in the IDMEF DTD as follows:
<!ELEMENT OverflowAlert (
program, size?, buffer?
)>
<!ATTLIST OverflowAlert
%attlist.global;
>
Analyzers use Heartbeat messages to indicate their current status to managers. Heartbeats are intended to be sent in a regular period, say, every ten minutes or every hour. The receipt of a Heartbeat message from an analyzer indicates to the manager that the analyzer is up and running; lack of a Heartbeat message (or more likely, lack of some number of consecutive Heartbeat messages) indicates that the analyzer or its network connection has failed.
All managers MUST support the receipt of Heartbeat messages; however, the use of these messages by analyzers is OPTIONAL. Developers of manager software SHOULD permit the software to be configured on a per-analyzer basis to use/not use Heartbeat messages.
A Heartbeat message is composed of several aggregate classes, as shown in Figure 6. The aggregate classes themselves are described in Sections 4.2.4 and 4.2.5.
+------------------+
| Heartbeat |
+------------------+ +------------------+
| STRING messageid |<>----------| Analyzer |
| | +------------------+
| | +------------------+
| |<>----------| CreateTime |
| | +------------------+
| | 0..1 +------------------+
| |<>----------| HeartbeatInterval|
| | +------------------+
| | 0..1 +------------------+
| |<>----------| AnalyzerTime |
| | +------------------+
| | 0..* +------------------+
| |<>----------| AdditionalData |
| | +------------------+
+------------------+
Figure 6: The Heartbeat Class
The aggregate classes that make up Heartbeat are:
Analyzer
Exactly one. Identification information for the analyzer that originated the heartbeat.
CreateTime
Exactly one. The time the heartbeat was created.
HeartbeatInterval
Zero or one. The interval in seconds at which heartbeats are generated.
AnalyzerTime
Zero or one. The current time on the analyzer (see Section 6.3).
AdditionalData
Zero or more. Information included by the analyzer that does not fit into the data model. This may be an atomic piece of data or a large amount of data provided through an extension to the IDMEF (see Section 5).
This is represented in the IDMEF DTD as follows:
<!ELEMENT Heartbeat (
Analyzer, CreateTime, HeartbeatInterval?, AnalyzerTime?,
AdditionalData*
)>
<!ATTLIST Heartbeat
messageid CDATA '0'
%attlist.global;
>
The Heartbeat class has one attribute:
messageid
Optional. A unique identifier for the heartbeat; see
Section 3.2.9.
The core classes -- Analyzer, Source, Target, Classification, and AdditionalData -- are the main parts of Alerts and Heartbeats, as shown in Figure 7.
+-----------+ +----------------+
| Heartbeat | +-------| Analyzer |
+-----------+ | +----------------+
| |<>---+--+
+-----------+ | | 0..* +----------------+
| +-------| AdditionalData |
| +----------------+
+-----------+ |
| Alert | | 0..* +----------------+
+-----------+ | +-------| Source |
| |<>---+ | +----------------+
| | | 0..* +----------------+
| | +-------| Target |
| | | +----------------+
| |<>------+
+-----------+ | +----------------+
+-------| Classification |
+----------------+
Figure 7: The Core Classes
The Analyzer class identifies the analyzer from which the Alert or Heartbeat message originates. Only one analyzer may be encoded for each alert or heartbeat, and that MUST be the analyzer at which the alert or heartbeat originated. Although the IDMEF data model does not prevent the use of hierarchical intrusion detection systems (where alerts get relayed up the tree), it does not provide any way to record the identity of the "relay" analyzers along the path from the originating analyzer to the manager that ultimately receives the alert.
The Analyzer class is composed of three aggregate classes, as shown in Figure 8.
+---------------------+
| Analyzer |
+---------------------+ 0..1 +----------+
| STRING analyzerid |<>----------| Node |
| STRING name | +----------+
| STRING manufacturer |
| STRING model | 0..1 +----------+
| STRING version |<>----------| Process |
| STRING class | +----------+
| STRING ostype | 0..1 +----------+
| STRING osversion |<>----------| Analyzer |
+---------------------+ +----------+
Figure 8: The Analyzer Class
The aggregate classes that make up Analyzer are:
Node
Zero or one. Information about the host or device on which the analyzer resides (network address, network name, etc.).
Process
Zero or one. Information about the process in which the analyzer is executing.
Analyzer
Zero or one. Information about the analyzer from which the message may have gone through. The idea behind this mechanism is that when a manager receives an alert and wants to forward it to another analyzer, it needs to substitute the original analyzer
information with its own. To preserve the original analyzer information, it may be included in the new analyzer definition. This will allow analyzer path tracking.
This is represented in the IDMEF DTD as follows:
<!ELEMENT Analyzer (
Node?, Process?, Analyzer?
)>
<!ATTLIST Analyzer
analyzerid CDATA '0'
name CDATA #IMPLIED
manufacturer CDATA #IMPLIED
model CDATA #IMPLIED
version CDATA #IMPLIED
class CDATA #IMPLIED
ostype CDATA #IMPLIED
osversion CDATA #IMPLIED
%attlist.global;
>
The Analyzer class has eight attributes:
analyzerid
Optional (but see below). A unique identifier for the analyzer; see Section 3.2.9.
This attribute is only "partially" optional. If the analyzer makes use of the "ident" attributes on other classes to provide unique identifiers for those objects, then it MUST also provide a valid "analyzerid" attribute. This requirement is dictated by the uniqueness requirements of the "ident" attribute (they are unique only within the context of a particular "analyzerid"). If the analyzer does not make use of the "ident" attributes, however, it may also omit the "analyzerid" attribute.
name
Optional. An explicit name for the analyzer that may be easier to understand than the analyzerid.
manufacturer
Optional. The manufacturer of the analyzer software and/or hardware.
model
Optional. The model name/number of the analyzer software and/or hardware.
version
Optional. The version number of the analyzer software and/or hardware.
class
Optional. The class of analyzer software and/or hardware.
ostype
Optional. Operating system name. On POSIX 1003.1 compliant systems, this is the value returned in utsname.sysname by the uname() system call, or the output of the "uname -s" command.
osversion
Optional. Operating system version. On POSIX 1003.1 compliant systems, this is the value returned in utsname.release by the uname() system call, or the output of the "uname -r" command.
The "manufacturer", "model", "version", and "class" attributes' contents are vendor-specific, but may be used together to identify different types of analyzers (and perhaps make determinations about the contents to expect in other vendor-specific fields of IDMEF messages).
The Classification class provides the "name" of an alert, or other information allowing the manager to determine what it is. This name is chosen by the alert provider.
The Classification class is composed of one aggregate class, as shown in Figure 9.
+----------------+
| Classification |
+----------------+ 0..* +-----------+
| STRING ident |<>----------| Reference |
| STRING text | +-----------+
+----------------+
Figure 9: The Classification Class
The aggregate class that makes up Classification is:
Reference
Zero or more. Information about the message, pointing to external documentation sites, that will provide background information about the alert.
This is represented in the IDMEF DTD as follows:
<!ELEMENT Classification (
Reference*
)>
<!ATTLIST Classification
ident CDATA '0'
text CDATA #REQUIRED
>
The Classification class has two attributes:
ident
Optional. A unique identifier for this classification; see Section 3.2.9.
text
Required. A vendor-provided string identifying the Alert message.
The Source class contains information about the possible source(s) of the event(s) that generated an alert. An event may have more than one source (e.g., in a distributed denial-of-service attack).
The Source class is composed of four aggregate classes, as shown in Figure 10.
+------------------+
| Source |
+------------------+ 0..1 +---------+
| STRING ident |<>----------| Node |
| ENUM spoofed | +---------+
| STRING interface | 0..1 +---------+
| |<>----------| User |
| | +---------+
| | 0..1 +---------+
| |<>----------| Process |
| | +---------+
| | 0..1 +---------+
| |<>----------| Service |
| | +---------+
+------------------+
Figure 10: The Source Class
The aggregate classes that make up Source are:
Node
Zero or one. Information about the host or device that appears to be causing the events (network address, network name, etc.).
User
Zero or one. Information about the user that appears to be causing the event(s).
Process
Zero or one. Information about the process that appears to be causing the event(s).
Service
Zero or one. Information about the network service involved in the event(s).
This is represented in the IDMEF DTD as follows:
<!ELEMENT Source (
Node?, User?, Process?, Service?
)>
<!ATTLIST Source
ident CDATA '0'
spoofed %attvals.yesno; 'unknown'
interface CDATA #IMPLIED
%attlist.global;
>
The Source class has three attributes:
ident
Optional. A unique identifier for this source; see Section 3.2.9.
spoofed
Optional. An indication of whether the source is, as far as the analyzer can determine, a spoofed address used for hiding the real origin of the attack. The permitted values for this attribute are shown below. The default value is "unknown". (See also Section 10.)
+------+---------+----------------------------------------+
| Rank | Keyword | Description |
+------+---------+----------------------------------------+
| 0 | unknown | Accuracy of source information unknown |
| | | |
| 1 | yes | Source is believed to be a decoy |
| | | |
| 2 | no | Source is believed to be "real" |
+------+---------+----------------------------------------+
interface
Optional. May be used by a network-based analyzer with multiple interfaces to indicate which interface this source was seen on.
The Target class contains information about the possible target(s) of the event(s) that generated an alert. An event may have more than one target (e.g., in the case of a port sweep).
The Target class is composed of four aggregate classes, as shown in Figure 11.
+------------------+
| Target |
+------------------+ 0..1 +----------+
| STRING ident |<>----------| Node |
| ENUM decoy | +----------+
| STRING interface | 0..1 +----------+
| |<>----------| User |
| | +----------+
| | 0..1 +----------+
| |<>----------| Process |
| | +----------+
| | 0..1 +----------+
| |<>----------| Service |
| | +----------+
| | 0..n +----------+
| |<>----------| File |
| | +----------+
+------------------+
Figure 11: The Target Class
The aggregate classes that make up Target are:
Node
Zero or one. Information about the host or device at which the event(s) (network address, network name, etc.) is being directed.
User
Zero or one. Information about the user at which the event(s) is being directed.
Process
Zero or one. Information about the process at which the event(s) is being directed.
Service
Zero or one. Information about the network service involved in the event(s).
File
Optional. Information about file(s) involved in the event(s).
This is represented in the IDMEF DTD as follows:
<!ELEMENT Target (
Node?, User?, Process?, Service?, File*
)>
<!ATTLIST Target
ident CDATA '0'
decoy %attvals.yesno; 'unknown'
interface CDATA #IMPLIED
%attlist.global;
>
The Target class has three attributes:
ident
Optional. A unique identifier for this target, see Section 3.2.9.
decoy
Optional. An indication of whether the target is, as far as the analyzer can determine, a decoy. The permitted values for this attribute are shown below. The default value is "unknown". (See also Section 10.)
+------+---------+----------------------------------------+
| Rank | Keyword | Description |
+------+---------+----------------------------------------+
| 0 | unknown | Accuracy of target information unknown |
| | | |
| 1 | yes | Target is believed to be a decoy |
| | | |
| 2 | no | Target is believed to be "real" |
+------+---------+----------------------------------------+
interface
Optional. May be used by a network-based analyzer with multiple interfaces to indicate which interface this target was seen on.
The Assessment class is used to provide the analyzer's assessment of an event -- its impact, actions taken in response, and confidence.
The Assessment class is composed of three aggregate classes, as shown in Figure 12.
+------------------+
| Assessment |
+------------------+ 0..1 +------------+
| |<>----------| Impact |
| | +------------+
| | 0..* +------------+
| |<>----------| Action |
| | +------------+
| | 0..1 +------------+
| |<>----------| Confidence |
| | +------------+
+------------------+
Figure 12: The Assessment Class
The aggregate classes that make up Assessment are:
Impact
Zero or one. The analyzer's assessment of the impact of the event on the target(s).
Action
Zero or more. The action(s) taken by the analyzer in response to the event.
Confidence
Zero or one. A measurement of the confidence the analyzer has in its evaluation of the event.
This is represented in the IDMEF DTD as follows:
<!ELEMENT Assessment (
Impact?, Action*, Confidence?
)>
<!ATTLIST Assessment
%attlist.global;
>
The AdditionalData class is used to provide information that cannot be represented by the data model. AdditionalData can be used to provide atomic data (integers, strings, etc.) in cases where only small amounts of additional information need to be sent; it can also be used to extend the data model and the DTD to support the transmission of complex data (such as packet headers). Detailed instructions for extending the data model and the DTD are provided in Section 5.
+------+-------------+----------------------------------------------+ | Rank | Keyword | Description | +------+-------------+----------------------------------------------+ | 0 | boolean | The element contains a boolean value, i.e., | | | | the strings "true" or "false" | | | | | | 1 | byte | The element content is a single 8-bit byte | | | | (see Section 3.2.4) | | | | | | 2 | character | The element content is a single character | | | | (see Section 3.2.3) | | | | | | 3 | date-time | The element content is a date-time string | | | | (see Section 3.2.6) | | | | | | 4 | integer | The element content is an integer (see | | | | Section 3.2.1) | | | | | | 5 | ntpstamp | The element content is an NTP timestamp (see | | | | Section 3.2.7) | | | | | | 6 | portlist | The element content is a list of ports (see | | | | Section 3.2.8) | | | | | | 7 | real | The element content is a real number (see | | | | Section 3.2.2) | | | | | | 8 | string | The element content is a string (see | | | | Section 3.2.3) | | | | | | 9 | byte-string | The element is a byte[] (see Section 3.2.4) | | | | | | 10 | xmltext | The element content is XML-tagged data (see | | | | Section 5.2) | +------+-------------+----------------------------------------------+
The AdditionalData element is declared in the IDMEF DTD as follows:
<!ENTITY % attvals.adtype "
( boolean | byte | character | date-time | integer | ntpstamp |
portlist | real | string | byte-string | xmltext )
">
<!ELEMENT AdditionalData (
(boolean | byte | character | date-time |
integer | ntpstamp | portlist | real |
string | byte-string | xmltext )
)>
<!ATTLIST AdditionalData
type %attvals.adtype; 'string'
meaning CDATA #IMPLIED
%attlist.global;
>
The AdditionalData class has one attribute:
meaning
Optional. A string describing the meaning of the element content. These values will be vendor/implementation dependent; the method for ensuring that managers understand the strings sent by analyzers is outside the scope of this specification. A list of acceptable meaning keywords is not within the scope of the document, although later versions may undertake to establish such a list.
The data model provides three classes for representing time. These classes are elements of the Alert and Heartbeat classes.
The time classes are represented in the IDMEF DTD as follows:
<!ELEMENT ntpstamp (#PCDATA) >
<!ATTLIST ntpstamp %attlist.global; >
<!ELEMENT CreateTime (#PCDATA) >
<!ATTLIST CreateTime
ntpstamp CDATA #REQUIRED
%attlist.global;
>
<!ELEMENT DetectTime (#PCDATA) >
<!ATTLIST DetectTime
ntpstamp CDATA #REQUIRED
%attlist.global;
>
<!ELEMENT AnalyzerTime (#PCDATA) >
<!ATTLIST AnalyzerTime
ntpstamp CDATA #REQUIRED
%attlist.global;
>
The DATETIME format of the <CreateTime> element content is described in Section 3.2.6.
If the date and time represented by the element content and the NTP timestamp differ (should "never" happen), the value in the NTP timestamp MUST be used.
The CreateTime class is used to indicate the date and time the alert or heartbeat was created by the analyzer.
The DetectTime class is used to indicate the date and time that the event(s) producing an alert was detected by the analyzer. In the case of more than one event, it is the time that the first event was detected. (This may or may not be the same time as CreateTime; analyzers are not required to send alerts immediately upon detection).
The AnalyzerTime class is used to indicate the current date and time on the analyzer. Its values should be filled in as late as possible in the message transmission process, ideally immediately before placing the message "on the wire".
The use of <AnalyzerTime> to perform rudimentary time synchronization between analyzers and managers is discussed in Section 6.3.
The data model provides three types of "assessments" that an analyzer can make about an event. These classes are aggregates of the Assessment class.
The Impact class is used to provide the analyzer's assessment of the impact of the event on the target(s). It is represented in the IDMEF DTD as follows:
<!ENTITY % attvals.severity "
( info | low | medium | high )
">
<!ENTITY % attvals.completion "
( failed | succeeded )
">
<!ENTITY % attvals.impacttype "
( admin | dos | file | recon | user | other )
">
<!ELEMENT Impact (#PCDATA) >
<!ATTLIST Impact
severity %attvals.severity; #IMPLIED
completion %attvals.completion; #IMPLIED
type %attvals.impacttype; 'other'
%attlist.global;
>
The Impact class has three attributes:
severity
An estimate of the relative severity of the event. The permitted values are shown below. There is no default value. (See also Section 10.)
+------+---------+-----------------------------------------+
| Rank | Keyword | Description |
+------+---------+-----------------------------------------+
| 0 | info | Alert represents informational activity |
| | | |
| 1 | low | Low severity |
| | | |
| 2 | medium | Medium severity |
| | | |
| 3 | high | High severity |
+------+---------+-----------------------------------------+
completion
An indication of whether the analyzer believes the attempt that the event describes was successful or not. The permitted values are shown below. There is no default value. (See also Section 10.)
+------+-----------+--------------------------------+
| Rank | Keyword | Description |
+------+-----------+--------------------------------+
| 0 | failed | The attempt was not successful |
| | | |
| 1 | succeeded | The attempt succeeded |
+------+-----------+--------------------------------+
type
The type of attempt represented by this event, in relatively broad categories. The permitted values are shown below. The default value is "other". (See also Section 10.)
+------+---------+--------------------------------------------------+ | Rank | Keyword | Description | +------+---------+--------------------------------------------------+ | 0 | admin | Administrative privileges were attempted or | | | | obtained | | | | | | 1 | dos | A denial of service was attempted or completed | | | | | | 2 | file | An action on a file was attempted or completed | | | | | | 3 | recon | A reconnaissance probe was attempted or | | | | completed | | | | | | 4 | user | User privileges were attempted or obtained | | | | | | 5 | other | Anything not in one of the above categories | +------+---------+--------------------------------------------------+
All three attributes are optional. The element itself may be empty, or may contain a textual description of the impact, if the analyzer is able to provide additional details.
The Action class is used to describe any actions taken by the analyzer in response to the event. Is is represented in the IDMEF DTD as follows:
<!ENTITY % attvals.actioncat "
( block-installed | notification-sent | taken-offline | other )
">
<!ELEMENT Action (#PCDATA) >
<!ATTLIST Action
category %attvals.actioncat; 'other'
%attlist.global;
>
Action has one attribute:
category
The type of action taken. The permitted values are shown below. The default value is "other". (See also Section 10.)
+------+-------------------+----------------------------------------+ | Rank | Keyword | Description | +------+-------------------+----------------------------------------+ | 0 | block-installed | A block of some sort was installed to | | | | prevent an attack from reaching its | | | | destination. The block could be a | | | | port block, address block, etc., or | | | | disabling a user account. | | | | | | 1 | notification-sent | A notification message of some sort | | | | was sent out-of-band (via pager, | | | | e-mail, etc.). Does not include the | | | | transmission of this alert. | | | | | | 2 | taken-offline | A system, computer, or user was taken | | | | offline, as when the computer is shut | | | | down or a user is logged off. | | | | | | 3 | other | Anything not in one of the above | | | | categories. | +------+-------------------+----------------------------------------+
The element itself may be empty, or may contain a textual description of the action, if the analyzer is able to provide additional details.
The Confidence class is used to represent the analyzer's best estimate of the validity of its analysis. It is represented in the IDMEF DTD as follows:
<!ENTITY % attvals.rating "
( low | medium | high | numeric )
">
<!ELEMENT Confidence (#PCDATA) >
<!ATTLIST Confidence
rating %attvals.rating; 'numeric'
%attlist.global;
>
The Confidence class has one attribute:
rating
The analyzer's rating of its analytical validity. The permitted values are shown below. The default value is "numeric". (See also Section 10.)
+------+---------+--------------------------------------------------+ | Rank | Keyword | Description | +------+---------+--------------------------------------------------+ | 0 | low | The analyzer has little confidence in its | | | | validity | | | | | | 1 | medium | The analyzer has average confidence in its | | | | validity | | | | | | 2 | high | The analyzer has high confidence in its validity | | | | | | 3 | numeric | The analyzer has provided a posterior | | | | probability value indicating its confidence in | | | | its validity | +------+---------+--------------------------------------------------+
This element should be used only when the analyzer can produce meaningful information. Systems that can output only a rough heuristic should use "low", "medium", or "high" as the rating value. In this case, the element content should be omitted.
Systems capable of producing reasonable probability estimates should use "numeric" as the rating value and include a numeric confidence value in the element content. This numeric value should reflect a posterior probability (the probability that an attack has occurred given the data seen by the detection system and the model used by the system). It is a floating point number between 0.0 and 1.0, inclusive. The number of digits should be limited to those representable by a single precision floating point value, and may be represented as described in Section 3.2.2.
NOTE: It should be noted that different types of analyzers may compute confidence values in different ways and that in many cases, confidence values from different analyzers should not be compared (for example, if the analyzers use different methods of computing or representing confidence, or are of different types or configurations). Care should be taken when implementing systems that process confidence values (such as event correlators) not to make comparisons or assumptions that cannot be supported by the system's knowledge of the environment in which it is working.
The support classes make up the major parts of the core classes, and are shared between them.
The Reference class provides the "name" of an alert, or other information allowing the manager to determine what it is.
The Reference class is composed of two aggregate classes, as shown in Figure 13.
+----------------+
| Reference |
+----------------+ +------+
| STRING origin |<>----------| name |
| STRING meaning | +------+
| | +------+
| |<>----------| url |
| | +------+
+----------------+
Figure 13: The Reference Class
The aggregate classes that make up Reference are:
name
Exactly one. STRING. The name of the alert, from one of the origins listed below.
url
Exactly one. STRING. A URL at which the manager (or the human operator of the manager) can find additional information about the alert. The document pointed to by the URL may include an in-depth description of the attack, appropriate countermeasures, or other information deemed relevant by the vendor.
This is represented in the IDMEF DTD as follows:
<!ENTITY % attvals.origin "
( unknown | vendor-specific | user-specific | bugtraqid | cve |
osvdb )
">
<!ELEMENT Reference (
name, url
)>
<!ATTLIST Reference
origin %attvals.origin; 'unknown'
meaning CDATA #IMPLIED
>
The Reference class has two attributes:
origin
Required. The source from which the name of the alert originates. The permitted values for this attribute are shown below. The default value is "unknown". (See also Section 10.)
+------+-----------------+------------------------------------------+
| Rank | Keyword | Description |
+------+-----------------+------------------------------------------+
| 0 | unknown | Origin of the name is not known |
| | | |
| 1 | vendor-specific | A vendor-specific name (and hence, URL); |
| | | this can be used to provide |
| | | product-specific information |
| | | |
| 2 | user-specific | A user-specific name (and hence, URL); |
| | | this can be used to provide |
| | | installation-specific information |
| | | |
| 3 | bugtraqid | The SecurityFocus ("Bugtraq") |
| | | vulnerability database identifier |
| | | (http://www.securityfocus.com/bid) |
| | | |
| 4 | cve | The Common Vulnerabilities and Exposures |
| | | (CVE) name (http://www.cve.mitre.org/) |
| | | |
| 5 | osvdb | The Open Source Vulnerability Database |
| | | (http://www.osvdb.org) |
+------+-----------------+------------------------------------------+
meaning
Optional. The meaning of the reference, as understood by the alert provider. This field is only valid if the value of the
<origin> attribute is set to "vendor-specific" or "user-specific".
The Node class is used to identify hosts and other network devices (routers, switches, etc.).
The Node class is composed of three aggregate classes, as shown in Figure 14.
+---------------+
| Node |
+---------------+ 0..1 +----------+
| STRING ident |<>----------| location |
| ENUM category | +----------+
| | 0..1 +----------+
| |<>----------| name |
| | +----------+
| | 0..* +----------+
| |<>----------| Address |
| | +----------+
+---------------+
Figure 14: The Node Class
The aggregate classes that make up Node are:
location
Zero or one. STRING. The location of the equipment.
name
Zero or one. STRING. The name of the equipment. This information MUST be provided if no Address information is given.
Address
Zero or more. The network or hardware address of the equipment. Unless a name (above) is provided, at least one address must be specified.
This is represented in the IDMEF DTD as follows:
<!ENTITY % attvals.nodecat "
( unknown | ads | afs | coda | dfs | dns | hosts | kerberos |
nds | nis | nisplus | nt | wfw )
">
<!ELEMENT Node (
location?, (name | Address), Address*
)>
<!ATTLIST Node
ident CDATA '0'
category %attvals.nodecat; 'unknown'
%attlist.global;
>
The Node class has two attributes:
ident
Optional. A unique identifier for the node; see Section 3.2.9.
category
Optional. The "domain" from which the name information was obtained, if relevant. The permitted values for this attribute are shown in the table below. The default value is "unknown". (See also Section 10 for extensions to the table.)
+------+----------+------------------------------------------+
| Rank | Keyword | Description |
+------+----------+------------------------------------------+
| 0 | unknown | Domain unknown or not relevant |
| | | |
| 1 | ads | Windows 2000 Advanced Directory Services |
| | | |
| 2 | afs | Andrew File System (Transarc) |
| | | |
| 3 | coda | Coda Distributed File System |
| | | |
| 4 | dfs | Distributed File System (IBM) |
| | | |
| 5 | dns | Domain Name System |
| | | |
| 6 | hosts | Local hosts file |
| | | |
| 7 | kerberos | Kerberos realm |
| | | |
| 8 | nds | Novell Directory Services |
| | | |
| 9 | nis | Network Information Services (Sun) |
| | | |
| 10 | nisplus | Network Information Services Plus (Sun) |
| | | |
| 11 | nt | Windows NT domain |
| | | |
| 12 | wfw | Windows for Workgroups |
+------+----------+------------------------------------------+
The Address class is used to represent network, hardware, and application addresses.
The Address class is composed of two aggregate classes, as shown in Figure 15.
+------------------+
| Address |
+------------------+ +---------+
| STRING ident |<>----------| address |
| ENUM category | +---------+
| STRING vlan-name | 0..1 +---------+
| INTEGER vlan-num |<>----------| netmask |
| | +---------+
+------------------+
Figure 15: The Address Class
The aggregate classes that make up Address are:
address
Exactly one. STRING. The address information. The format of this data is governed by the category attribute.
netmask
Zero or one. STRING. The network mask for the address, if appropriate.
This is represented in the IDMEF DTD as follows:
<!ENTITY % attvals.addrcat "
( unknown | atm | e-mail | lotus-notes | mac | sna | vm |
ipv4-addr | ipv4-addr-hex | ipv4-net | ipv4-net-mask |
ipv6-addr | ipv6-addr-hex | ipv6-net | ipv6-net-mask )
">
<!ELEMENT Address (
address, netmask?
)>
<!ATTLIST Address
ident CDATA '0'
category %attvals.addrcat; 'unknown'
vlan-name CDATA #IMPLIED
vlan-num CDATA #IMPLIED
%attlist.global;
>
The Address class has four attributes:
ident
Optional. A unique identifier for the address; see Section 3.2.9.
category
Optional. The type of address represented. The permitted values for this attribute are shown below. The default value is "unknown". (See also Section 10.)
+------+---------------+--------------------------------------------+
| Rank | Keyword | Description |
+------+---------------+--------------------------------------------+
| 0 | unknown | Address type unknown |
| | | |
| 1 | atm | Asynchronous Transfer Mode network address |
| | | |
| 2 | e-mail | Electronic mail address (RFC 2822 [12]) |
| | | |
| 3 | lotus-notes | Lotus Notes e-mail address |
| | | |
| 4 | mac | Media Access Control (MAC) address |
| | | |
| 5 | sna | IBM Shared Network Architecture (SNA) |
| | | address |
| | | |
| 6 | vm | IBM VM ("PROFS") e-mail address |
| | | |
| 7 | ipv4-addr | IPv4 host address in dotted-decimal |
| | | notation (a.b.c.d) |
| | | |
| 8 | ipv4-addr-hex | IPv4 host address in hexadecimal notation |
| | | |
| 9 | ipv4-net | IPv4 network address in dotted-decimal |
| | | notation, slash, significant bits |
| | | (a.b.c.d/nn) |
| | | |
| 10 | ipv4-net-mask | IPv4 network address in dotted-decimal |
| | | notation, slash, network mask in |
| | | dotted-decimal notation (a.b.c.d/w.x.y.z) |
| | | |
| 11 | ipv6-addr | IPv6 host address |
| | | |
| 12 | ipv6-addr-hex | IPv6 host address in hexadecimal notation |
| | | |
| 13 | ipv6-net | IPv6 network address, slash, significant |
| | | bits |
| | | |
| 14 | ipv6-net-mask | IPv6 network address, slash, network mask |
+------+---------------+--------------------------------------------+
vlan-name
Optional. The name of the Virtual LAN to which the address belongs.
vlan-num
Optional. The number of the Virtual LAN to which the address belongs.
The User class is used to describe users. It is primarily used as a "container" class for the UserId aggregate class, as shown in Figure 16.
+---------------+
| User |
+---------------+ 1..* +--------+
| STRING ident |<>----------| UserId |
| ENUM category | +--------+
+---------------+
Figure 16: The User Class
The aggregate class contained in User is:
UserId
One or more. Identification of a user, as indicated by its type attribute (see Section 4.2.7.3.1).
This is represented in the IDMEF DTD as follows:
<!ENTITY % attvals.usercat "
( unknown | application | os-device )
">
<!ELEMENT User (
UserId+
)>
<!ATTLIST User
ident CDATA '0'
category %attvals.usercat; 'unknown'
%attlist.global;
>
The User class has two attributes:
ident
Optional. A unique identifier for the user; see Section 3.2.9.
category
Optional. The type of user represented. The permitted values for this attribute are shown below. The default value is "unknown". (See also Section 10.)
+------+-------------+------------------------------------+
| Rank | Keyword | Description |
+------+-------------+------------------------------------+
| 0 | unknown | User type unknown |
| | | |
| 1 | application | An application user |
| | | |
| 2 | os-device | An operating system or device user |
+------+-------------+------------------------------------+
The UserId class provides specific information about a user. More than one UserId can be used within the User class to indicate attempts to transition from one user to another, or to provide complete information about a user's (or process') privileges.
The UserId class is composed of two aggregate classes, as shown in Figure 17.
+--------------+
| UserId |
+--------------+ 0..1 +--------+
| STRING ident |<>----------| name |
| ENUM type | +--------+
| STRING tty | 0..1 +--------+
| |<>----------| number |
| | +--------+
+--------------+
Figure 17: The UserId Class
The aggregate classes that make up UserId are:
name
Zero or one. STRING. A user or group name.
number
Zero or one. INTEGER. A user or group number.
This is represented in the IDMEF DTD as follows:
<!ENTITY % attvals.idtype "
( current-user | original-user | target-user | user-privs |
current-group | group-privs | other-privs )
">
<!ELEMENT UserId (
(name, number?) | (number, name?)
)>
<!ATTLIST UserId
ident CDATA '0'
type %attvals.idtype; 'original-user'
tty CDATA #IMPLIED
%attlist.global;
>
The UserId class has three attributes:
ident
Optional. A unique identifier for the user id, see Section 3.2.9.
type
Optional. The type of user information represented. The permitted values for this attribute are shown below. The default value is "original-user". (See also Section 10.)
+------+---------------+--------------------------------------------+ | Rank | Keyword | Description | +------+---------------+--------------------------------------------+ | 0 | current-user | The current user id being used by the user | | | | or process. On Unix systems, this would | | | | be the "real" user id, in general. | | | | | | 1 | original-user | The actual identity of the user or process | | | | being reported on. On those systems that | | | | (a) do some type of auditing and (b) | | | | support extracting a user id from the | | | | "audit id" token, that value should be | | | | used. On those systems that do not | | | | support this, and where the user has | | | | logged into the system, the "login id" | | | | should be used. | | | | | | 2 | target-user | The user id the user or process is | | | | attempting to become. This would apply, | | | | on Unix systems for example, when the user | | | | attempts to use "su", "rlogin", "telnet", | | | | etc. | | | | | | 3 | user-privs | Another user id the user or process has | | | | the ability to use, or a user id | | | | associated with a file permission. On | | | | Unix systems, this would be the | | | | "effective" user id in a user or process | | | | context, and the owner permissions in a | | | | file context. Multiple UserId elements of | | | | this type may be used to specify a list of | | | | privileges. | | | | | | 4 | current-group | The current group id (if applicable) being | | | | used by the user or process. On Unix | | | | systems, this would be the "real" group | | | | id, in general. | | | | | | 5 | group-privs | Another group id the group or process has | | | | the ability to use, or a group id | | | | associated with a file permission. On | | | | Unix systems, this would be the | | | | "effective" group id in a group or process | | | | context, and the group permissions in a | | | | file context. On BSD-derived Unix | | | | systems, multiple UserId elements of this | | | | type would be used to include all the | | | | group ids on the "group list". |
| 6 | other-privs | Not used in a user, group, or process | | | | context, only used in the file context. | | | | The file permissions assigned to users who | | | | do not match either the user or group | | | | permissions on the file. On Unix systems, | | | | this would be the "world" permissions. | +------+---------------+--------------------------------------------+
tty
Optional. STRING. The tty the user is using.
The Process class is used to describe processes being executed on sources, targets, and analyzers.
The Process class is composed of five aggregate classes, as shown in Figure 18.
+--------------+
| Process |
+--------------+ +------+
| STRING ident |<>----------| name |
| | +------+
| | 0..1 +------+
| |<>----------| pid |
| | +------+
| | 0..1 +------+
| |<>----------| path |
| | +------+
| | 0..* +------+
| |<>----------| arg |
| | +------+
| | 0..* +------+
| |<>----------| env |
| | +------+
+--------------+
Figure 18: The Process Class
The aggregate classes that make up Process are:
name
Exactly one. STRING. The name of the program being executed. This is a short name; path and argument information are provided elsewhere.
pid
Zero or one. INTEGER. The process identifier of the process.
path
Zero or one. STRING. The full path of the program being executed.
arg
Zero or more. STRING. A command-line argument to the program. Multiple arguments may be specified (they are assumed to have occurred in the same order they are provided) with multiple uses of arg.
env
Zero or more. STRING. An environment string associated with the process; generally of the format "VARIABLE=value". Multiple environment strings may be specified with multiple uses of env.
This is represented in the IDMEF DTD as follows:
<!ELEMENT Process (
name, pid?, path?, arg*, env*
)>
<!ATTLIST Process
ident CDATA '0'
%attlist.global;
>
The Process class has one attribute:
ident
Optional. A unique identifier for the process; see Section 3.2.9.
The Service class describes network services on sources and targets. It can identify services by name, port, and protocol. When Service occurs as an aggregate class of Source, it is understood that the service is one from which activity of interest is originating; and that the service is "attached" to the Node, Process, and User information also contained in Source. Likewise, when Service occurs as an aggregate class of Target, it is understood that the service is one to which activity of interest is being directed; and that the service is "attached" to the Node, Process, and User information also contained in Target. If Service occurs in both Source and Target, then information in both locations should be the same. If information is the same in both locations and implementers wish to carry it in only one location, they should specify it as an aggregate of the Target class.
The Service class is composed of four aggregate classes, as shown in Figure 19.
+-----------------------------+
| Service |
+-----------------------------+ 0..1 +----------+
| STRING ident |<>----------| name |
| INTEGER ip_version | +----------+
| INTEGER iana_protocol_number| 0..1 +----------+
| STRING iana_protocol_name |<>----------| port |
| | +----------+
| | 0..1 +----------+
| |<>----------| portlist |
| | +----------+
| | 0..1 +----------+
| |<>----------| protocol |
| | +----------+
+-----------------------------+
/_\
|
+---------+--------+
| |
+-------------+ +-------------+
| SNMPService | | WebService |
+-------------+ +-------------+
Figure 19: The Service Class
The aggregate classes that make up Service are:
name
Zero or one. STRING. The name of the service. Whenever possible, the name from the IANA list of well-known ports SHOULD be used.
port
Zero or one. INTEGER. The port number being used.
portlist
Zero or one. PORTLIST. A list of port numbers being used; see Section 3.2.8 for formatting rules. If a portlist is given, the iana_protocol_number and iana_protocol_name MUST apply to all the elements of the list.
protocol
Zero or one. STRING. Additional information about the protocol being used. The intent of the protocol field is to carry additional information related to the protocol being used when the
<Service> attributes iana_protocol_number or/and
iana_protocol_name are filed.
A Service MUST be specified as either (a) a name or a port or (b) a portlist. The protocol is optional in all cases, but no other combinations are permitted.
Service is represented in the IDMEF DTD as follows:
<!ELEMENT Service (
(((name, port?) | (port, name?)) | portlist), protocol?,
SNMPService?, WebService?
)>
<!ATTLIST Service
ident CDATA '0'
ip_version CDATA #IMPLIED
iana_protocol_number CDATA #IMPLIED
iana_protocol_name CDATA #IMPLIED
%attlist.global;
>
The Service class has four attributes:
ident
Optional. A unique identifier for the service; see Section 3.2.9.
ip_version
Optional. INTEGER. The IP version number.
iana_protocol_number
Optional. INTEGER. The IANA protocol number.
iana_protocol_name
Optional. STRING. The IANA protocol name.
The WebService class carries additional information related to web traffic.
The WebService class is composed of four aggregate classes, as shown in Figure 20.
+-------------+
| Service |
+-------------+
/_\
|
+-------------+
| WebService |
+-------------+ +-------------+
| |<>----------| url |
| | +-------------+