Internet-Draft Wood, M.
Internet Engineering Task Force Internet Security Systems
Intrusion Detection Exchange Format Working Group June, 1999
Category: Informational
Intrusion Detection Exchange Format Requirements
<draft-ietf-idwg-requirements-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
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Distribution of this memo is unlimited.
This Internet Draft expires December 22, 1999.
1. Abstract
The purpose of the Intrusion Detection Exchange Format is to
define data formats and exchange procedures for sharing
information of interest to intrusion detection and response
systems, and to the management systems which may need to interact
with them. This Internet-Draft describes the high-level
requirements for such communication, including the rationale for
those requirements. Scenarios are used to illustrate the
requirements.
2. Conventions used in this document
The key words "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].
Wood Informational - December 22, 1999 1
3. Introduction
This document defines requirements for the Intrusion Detection Exchange
Format (IDEF), which is the intended work product of the Intrusion
Detection Exchange Format Working Group (IDWG). IDEF is planned to be
a standard format which automated Intrusion Detection Systems can use
for reporting events which they have deemed to be suspicious.
3.1 Rationale
The reasons such a format should be useful are as follows:
1) A number of commercial and free Intrusion Detection Systems (IDS) are
available and more are coming onto the market all the time. Some
products are aimed at detecting intrusions on the network, others
are aimed at host operating systems, while still others are aimed at
applications. Even within a given category, the products have very
different strengths and weaknesses. Hence it is likely that customers
will buy more than a single product. And customers will want to
observe the output of these products from a one or more console(s). A
standard format for reporting events will simplify this task greatly.
2) Intrusions frequently involve multiple organizations as victims, or
multiple sites within the same organization. Typically, those sites
will use different ID systems. It would be very helpful to correlate
such distributed intrusions across multiple sites and administrative
domains. Having reports from all sites in a common format would
facilitate this task
3) The existence of a common format should allow components from
different ID systems to be integrated more readily. ID research
should be able to be integrated into commercial products more easily.
4) We feel that, in addition to enabling communication from an ID
analyzer to an ID manager, the IDEF notification system may also
enable communications between a variety of IDS components. However,
for the remainder of this document, we refer to the communications as
going from an analyzer to a manager.
All of these reasons suggest that a common format for reporting
suspicious events should help the IDS market to grow and innovate more
successfully, and should result in IDS users obtaining better results
from deployment of ID systems.
3.2 Intrusion Detection Terms
In order to make the rest of the requirements clearer, we define some
terms about typical intrusion detection systems.
3.2.1 Activity:
Instantiations of the data source that are identified by the analyzer as
being of interest to the operator. Examples of this include (but are not
limited to) network sessions, user activity, and application events.
Wood Informational - December 22, 1999 2
Activity can range from extremely serious occurrences (such as a
unequivocally malicious attack) to less serious occurrences (such as
unusual user activity that's worth a further look).
3.2.2 Administrator:
The human with responsibility for the day-to-day maintenance and
management of organizational security. This individual may or may not
be the same person charged with the deployment of the intrusion
detection system and may or may not be the same person that is actually
monitoring the output of the IDS. In some organizations, the
administrator is associated with the network or systems administration
groups. In other organizations, it's an independent position.
3.2.3 Alert:
A message from an analyzer to a manager that an event has been detected.
An alert typically contains information about the unusual activity that
was detected, as well as the specifics of the occurrence.
3.2.4 Analyzer:
The ID component that analyzes the data collected by the sensor for
signs of unauthorized or undesired activity or for events that might be
of interest to the security administrator. In many existing ID systems,
the sensor and the analyzer are part of the same component. In this
document, the term analyzer is used generically to refer to the sender
of the IDEF message.
3.2.5 Data Source:
The raw information that an intrusion detection system uses to detect
unauthorized or undesired activity. Common data sources include (but
are not limited to) raw network packets, operating system audit logs,
application audit logs, and system-generated checksum data.
3.2.6 Event:
The occurrence in the data source that is detected by the analyzer and
which may result in an IDEF alert being transmitted. For example, three
failed logins in 10 seconds might indicate a brute-force login attack
3.2.7 Manager:
The ID component from which the security administrator manages the
various components of the ID system. Management functions typically
include (but are not limited to) sensor configuration, analyzer
configuration, event notification management, data consolidation, and
reporting.
3.2.8 Notification:
The method by which the IDS manager makes the operator aware of the
event occurrence. In many ID systems, this is done via the display of a
Wood Informational - December 22, 1999 3
colored icon on the IDS manager screen, the transmission of an e-mail or
pager message, or the transmission of an SNMP trap, although other
notification techniques are also used.
3.2.9 Operator:
The human that is the primary user of the IDS manager. The operator
often monitors the output of the ID system and initiates or recommends
further action.
3.2.10 Response:
The actions taken in response to an event. Responses may be undertaken
automatically by some entity in the ID system architecture or may be
initiated by a human. Sending a notification to the operator is a very
common response. Other responses include (but are not limited to)
logging the activity, recording the raw data (from the data source) that
characterized the event, terminating a network, user, or application
session, or altering network or system access controls.
3.2.11 Sensor:
The ID component that collects data from the data source. The
frequency of data collection will vary across IDS offerings.
3.2.12 Signature:
A rule used by the analyzer to identify interesting activity to the
security administrator. Signatures represent one of the mechanisms
(though not necessarily the only mechanism) by which ID systems detect
intrusions.
3.2.13 Security Policy:
The predefined, formally documented statement which defines what
services are allowed to be transported across the monitored segment of
the network to support the business requirement. This includes, but it
not limited to, which hosts are to be denied external network access.
3.3 Architectural Assumptions
In this document, as defined in the terms above, we assume that an
analyzer determines somehow that a suspicious event has been seen by a
sensor, and sends an alert to a management console. The format of that
alert is what IDEF proposes to standardize.
For the purposes of this document, we assume that the analyzer and
management console are separate components, and that they are
communicating pairwise across a TCP/IP network. No other form of
communication between these entities is contemplated in this document,
and no other use of IDEF alerts is considered.
We try to make no further architectural assumptions than those just
stated. For example, the following points should not matter:
Wood Informational - December 22, 1999 4
* Whether the sensor and the analyzer are integrated or separate.
* Whether the analyzer and management console are isolated, or
embedded in some large hierarchy or distributed mesh of components.
* Whether the management console actually notifies a human, takes
action automatically, or just analyzes incoming alerts and
correlates them.
* A component might act as an analyzer with respect to one component,
but as a management console with respect to another.
3.4 Organization of this document.
Besides this requirements document, the IDWG working group should
produce two other documents. The first should describe a data format or
language for exchanging information about suspicious events. In this
document, we refer to that as the "data-format specification". The
second document should identify existing IETF protocols that are best
used for conveying the data so formatted, and explain how to package
this data in those existing formats. We refer to this as the
"communication specification".
Accordingly, the requirements here are partitioned into five sections
* The first of these contains general requirements that apply to all
aspects of the IDEF specification.
* The second section describes requirements on the formatting of IDEF
messages.
* The third section outlines requirements on the transport of IDEF
messages from the analyzer to the manager.
* The fourth section contains requirements on the content and
semantics of the IDEF messages.
* The final section places requirements on IDEF event definitions and
the event definition process.
For each requirement, we attempt to state the requirement as clearly as
possible without imposing an idea of what a design solution should be.
Then we give the rationale for why this requirement is important, and
state whether this should be an essential feature of the specification,
or is beneficial but could be lacking if it is difficult to fulfill.
Finally, where it seems necessary, we give an illustrative scenario.
4. General Requirements
4.1 The IDEF shall reference and use previously published RFCs where
possible.
4.1.1 Rationale: The IETF has already completed a great deal of research
and work into the areas of networks and security. In the interest
Wood Informational - December 22, 1999 5
of time, it is smart business to implement already defined and
accepted standards.
4.1.2 Scenario:
4.2 The IDEF must operate in environments that contain IPv6
implementations.2.2.1 Rationale: Since pure IPv4, hybrid
IPv6/IPv4, and pure IPv6 environments are expected to exist
within the timeframe of IDEF implementations, the IDEF
specification must support IPv6 environments.
4.2.2 Scenario:
5. Message Format
5.1 IDEF message formats shall support full internationalization and
localization.
5.1.1 Rationale: Since network security and intrusion detection are
areas that cross geographic, political, and cultural boundaries,
the IDEF messages must be formatted such that they can be
presented to an operator in a local language and adhering to local
presentation customs.
5.1.2 Scenario:
5.2 The format of IDEF messages must support filtering and/or
aggregation of data by the manager.
5.2.1 Rationale: Since it is anticipated that some managers may want to
perform filtering and/or data aggregation functions on IDEF
messages, the IDEF messages must be structured to facilitate these
operations.
5.2.2 Scenario:
6. Transport Requirements
6.1 The IDEF must support reliable transmission of messages.
6.1.1 Rationale: IDS managers often rely on receipt of data from IDS
analyzers to do their jobs effectively. Since IDS managers will
rely on IDEF messages for this purpose, it is important,
therefore, that IDEF messages be delivered reliably.
6.1.2 Scenario: The IDEF system might rely upon TCP reliability
mechanisms or might design its own reliable protocol for use with
UDP.
Wood Informational - December 22, 1999 6
6.2 The IDEF must support transmission of messages from analyzers
outside firewalls to managers inside firewalls without requiring
changes to the firewall configuration that weaken the security of
the perimeter. The IDEF design must also be relatively easy to
implement.
6.2.1 Rationale: Since IDEF analyzers are often placed outside firewalls
and since it is expected that IDEF managers will most often be
located inside firewalls, it is necessary that analyzers be able
to send IDEF messages through a firewall. Setting up this
communication must not require changes to the configuration of the
intervening firewall(s) that weaken the security of the protected
network.
6.2.2 Scenario: One possible scenario is the use of TCP to convey IDEF
messages. If the destination ports of this communications channel
are user-programmable, it may be possible for the IDEF system to
use existing firewall tunnels without change to the firewall
configuration.
6.3 The IDEF must support peer-to-peer authentication of the analyzer
to the manager.
6.3.1 Rationale: Since the alert messages are used by a manager to
direct responses or further investigation related to the security
of an enterprise network, it is important that the receiver have
confidence in the identity of the sender. This is peer-to-peer
authentication of the sender to the receiver. It must not be
based on authentication of the underlying transport, for example,
because of the risk that this authentication process may be
subverted or misconfigured.
6.3.2 Scenario: Analyzer process authenticates itself to manager process
via public key exchange or some other method.
6.4 The IDEF must maintain confidentiality of the message content. The
selected design must be capable of supporting a variety of
encryption algorithms and must be adaptable to a wide variety of
environments.
6.4.1 Rationale: IDEF messages potentially contain extremely sensitive
information (such as passwords) and would be of great interest to
an intruder. Since it is likely some of these messages will be
transmitted across uncontrolled network segments, it is important
that the content be shielded. Furthermore, since the legal
environment for encryption technologies is extremely varied and
changes often, it is important that the design selected be capable
of supporting a number of different encryption options and be
adaptable by the user to a variety of environments.
6.4.2 Scenario: The IDEF system might offer two different encryption
modules, one using 168-bit keys and another using 56-bit keys.
Wood Informational - December 22, 1999 7
6.5 The IDEF must ensure the integrity of the message content. The
selected design must be capable of supporting a variety of
integrity algorithms and must be adaptable to a wide variety of
environments.
6.5.1 Rationale: IDEF messages are used by the manager to direct action
related to the security of the protected enterprise network. It is
vital for the manager to be certain that the content of the
message has not been changed after transmission.
6.5.2 Scenario: An integrity hash, such as the MD5 algorithm, might be
part of the IDEF design.
6.6 The IDEF should ensure non-repudiation of the message
transmission.
6.6.1 Rationale:
6.6.2 Scenario:
6.7 The IDEF communications mechanism should resist protocol denial of
service attacks.
6.7.1 Rationale:
6.7.2 Scenario:
6.8 The IDEF communications mechanism should resist malicious
duplication of messages.
6.8.1 Rationale:
6.8.2 Scenario:
7. Message Content
7.1 The IDEF message must encompass all types of intrusion detection
mechanisms.
7.1.1 Rationale: There are many types of intrusion detection systems
that analyze a variety of data sources. Some are profile based and
operate on log files, attack signatures etc. Others are anomaly
based and define normal behavior and detect deviations from the
established baseline. Each of these systems report different data
that, in part, depends on their intrusion detection methodology.
All must be supported by this standard.
7.1.2 Scenario: An attacker invents a new attack. The profile-based
system does not detect it. An anomaly-based system detects the
Wood Informational - December 22, 1999 8
novel attack but it cannot provide an attack type in an alert
message.
7.2 The IDEF must support reporting event creation date and time in
each event. The IDEF may support reporting the attack detection
date and time in addition to the event creation date and time.
Time shall be reported as the localtime and time zone offset on
the system generating the message. [See RFC 1902 for guidelines on
reporting time.] (supporting reporting across multiple timezones
and correlating across multiple timezones)
The format for reporting the date must be compliant with all
current standards for Year 2000 rollover, and it must have
sufficient capability to continue reporting date values past the
year 2038.
Time granularity in event messages shall not be specified by the
IDEF.
7.2.1 Rationale: Time is important from both a reporting and correlation
point of view. Attack detection time may differ from the event
creation time as it may take some time to actually generate the
event message given that an attack has been detected. If the
sensing element can determine the time the attack occurred it is
strongly encouraged to place that information in the attack
detection field. The IDEF cannot assume a certain clock
granularity on sensing elements, and so cannot impose any
requirements on the granularity of the event timestamps.
7.2.2 Scenario:
7.3 The IDEF message must provide information about the automatic
actions taken by the analyzer in response to the event (if any).
7.3.1 Rationale: It is very important for the operator to know if
there was an automated response and what that response was. This
will help determine what further action to take, if any.
7.3.2 Scenario: The attacker launches the attack, the ID system detects
the attack and disables the user account performing the suspicious
activity. This suspension is for 10 minutes to allow the operator
time to investigate the suspicious activity. The IDEF message
contains this information.
7.4 The IDEF message must contain an indication of the potential
impact of the attack, if it is known.
7.4.1 Rationale: Information concerning the possible impact of the
attack on the target system provides an indication of what the
attacker is attempting to do and is critical data for the operator
to perform damage assessment. Not all systems will be able to
Wood Informational - December 22, 1999 9
determine this, but it is important data to transmit for those
systems that can.
7.4.2 Scenario: A buffer overflow attack is launched and detected by the
ID analyzer. The IDEF message may contain information that this
buffer overflow attack is an attempt to gain root or administrator
privilege on the target system. The ID operator may use this data
increase the priority of the response.
7.5 The IDEF message must contain the identity of the vendor and the
tool that detected the attack.
7.5.1 Rationale: Users may run multiple intrusion detection systems to
protect their enterprise. This data will help the systems
administrator determine which vendor and tool detected the attack.
7.5.2 Scenario: Tool X from vendor Y detects a potential intrusion. A
message is sent reporting that it found a potential break-in with
X and Y specified. The operator is therefore able to include the
known capabilities or weaknesses of tool X in his decision
regarding further action.
7.6 The IDEF message must support a vendor extension mechanism used to
define vendor specific data. The use of this mechanism by the
vendor is optional. This data contains vendor specific information
determined by each vendor. The vendors must indicate how to
interpret these extensions.
7.6.1 Rationale: Vendors may wish to supply extra data such as the
version number of their product or other data that they believe
provides value added due to the specific nature of their product.
7.6.2 Scenario: The vendor passes back detailed information specific to
their product after it detects a potential attack.
7.7 The IDEF message may include a list of sensors that sensed the
event. This sensor list must be designated by a list of IP
addresses.
7.7.1 Rationale: Intrusion detection sensors and analysis engines are
often not co-located. It is important to know where the event was
sensed.
7.7.2 Scenario: A distributed intrusion detection system has sensors
placed throughout the enterprise. Detection of a sophisticated
attack might actually involve passing of data through many
analyzers, each of which performs a specific piece of analysis.
The ultimate reporting of this event to the ID manager might
include the IP addresses of all the analyzers involve in the
detection. This information might be used by the manager to
localize the attack to a specific portion of the network.
Wood Informational - December 22, 1999 10
7.8 The content of IDEF messages must contain the identified name of
the attack if it is known. This name will be drawn from a
standardized list of attacks or will be a vendor-specific name if
the attack identity has not yet been standardized. It is not known
how this list will be defined or updated, although requirements on
the creation of this list are presented in the next section of
this document. In addition, the message must contain the attack
technique if it is known. The attack technique will also be
selected from a list of attack technique identifiers.
7.8.1 Rationale: Given than this document presents requirements on
standardizing ID message formats so that an ID manager may receive
alerts from analyzers from multiple vendors, it is important that
the manager understand the semantics of the reported events. There
is, therefore, a need to identify known attacks and store
information concerning their method and possible fixes to these
attacks. Some attacks are well known and this recognition can help
the operator. The operator can also benefit from knowing the
attack technique (e.g. flooding).
7.8.2 Scenario: Attacker launches an attack that is detected by two
different analyzers from two distinct vendors. Both report the
same event identity to the ID manager, even though the algorithms
used to detect the attack by each analyzer may have been
different.
7.9 The IDEF message must contain the identity of the source of the
attack and target component identifier if it is known. In the case
of a network-based attack, this will be the source and destination
IP address of the session used to launch the attack. Note that the
identify of source and target will vary for other types of
attacks, such as those launched/detected at the operating system
or application level.
7.9.1 Rationale: This will allow the operator to identify the source and
target of the attack.
7.9.2 Scenario: Attacker launches a network attack against a DNS server
using a buffer overflow attack. The IDEF alert message indicates
the DNS server as the target and includes the source IP address
used to launch the attack.
7.10 The IDEF message must contain the ability to reference additional
detailed data related to this specific underlying event. It is
optional for vendors to use this field.
7.10.1 Rationale: Operators may want more information on specifics of
the attack. This field, if filled in by the analyzer, may point
to additional or more detailed information about the intrusion
Wood Informational - December 22, 1999 11
7.10.2 Scenario: Attacker attacks host and is detected by ID system.
IDEF message contains a pointer to a set of records that gives
access to system audit data.
7.11 The semantics of the IDEF message must be well defined.
7.11.1 Rationale: Good semantics are key to understanding what the
message is trying to convey so there are no errors due to
confusion over exactly what the message means. Operators will
decide what action to take based on these messages, so it is
important that they can interpret them correctly.
7.11.2 Scenario: Without this requirement, the operator receives an IDEF
message and interprets it one way. The vendor who constructed the
message intended it to have a different meaning from the system
administrator's interpretation. The resulting corrective action
is, therefore, incorrect.
7.12 The IDEF message must contain a field for an advisory from a
noted authority such as the CERT. The vendor must fill in this
field if the information is available and applicable to the event
being reported.
7.12.1 Rationale: This information is used by administrators to report
and fix problems.
7.12.2 Scenario: Attacker performs a well-known attack. CERT advisory
number is included in IDEF message since the vendor has access to
a list of CERT advisory numbers. Operator uses this information
to initiate repairs on the vulnerable system.
7.13 The IDEF message must contain a field for data on the degree of
penetration achieved by the attack. The vendors have the option
of specifying this data.
7.13.1 Rationale: This information is valuable to determine the extent
of damage to the system. Sometimes the attack fails and other
times the attack is very successful and causes significant
damage. Note that this information is not always available at the
time or place the IDEF message is constructed.
7.13.2 Scenario: Attempt to break into host system fails. This is
reported in the IDEF message with degree of penetration equal to
zero. The operator reduces the priority of this event, since it
appears no damage was done.
7.14 The IDEF message must contain a field for data on the degree of
confidence of the report. The completion of this field by an
analyzer is optional, as this data may not be available at all
analyzers.
Wood Informational - December 22, 1999 12
7.14.1 Rationale: Many ID systems contain thresholds to determine
whether or not to generate an alert. This may influence the
degree of confidence one has in the report or perhaps would
indicate the likelihood of the report being a false alarm.
7.14.2 Scenario: The alarm threshold monitor is set at a low level to
indicate that an organization wants reports on any suspicious
activity, regardless of the probability of a real attack. The
degree of confidence measure is used to indicate if this is a low
probability or high probability attack.
8. Event Definitions and the Event-Definition Process
8.1 The IDEF must be extensible. As new events are defined by the
community and as new methods of detecting them are offered by the
industry, the IDEF must be able to grow with the technology.
8.1.1 Rationale:
6.1.2 Scenario:
8.2 The standard event definitions must be extensible by vendors and
users.
8.2.1 Rationale:
8.2.2 Scenario:
8.3 The process by which new events are defined and standardized must
be vendor independent.
8.3.1 Rationale:
8.3.2 Scenario:
9. References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
Wood Informational - December 22, 1999 13
Acknowledgements:
The following individuals contributed substantially to this document and
should be recognized for their efforts. This document would not exist
without their help:
Mark Crosbie, Hewlett-Packard
David Donahoo, Air Force Information Warfare Center
Mike Erlinger, Harvey Mudd College
Dipankar Gupta, Hewlett-Packard
Stuart Staniford-Chen, Silicon Defense
Maureen Stillman, Odyssey Research Associates
Editor's Address:
Mark Wood
Internet Security Systems, Inc.
6600 Peachtree-Dunwoody Road
300 Embassy Row
Atlanta, GA 30328
Phone: +1 (678) 443-6147
E-mail: mark1@iss.net
Intrusion Detection Exchange Format Working Group:
The Intrusion Detection Exchange Format Working Group can be contacted
via the working group's mailing list (idwg-public@zurich.ibm.com) or
through its chairs:
Stuart Staniford-Chen
stuart@SiliconDefense.com
Silicon Defense
Mike Erlinger
mike@cs.hmc.edu
Harvey Mudd College
Full Copyright Statement
Copyright (C) The Internet Society (1999). All Rights Reserved. This
document and translations of it may be copied and furnished to others,
and derivative works that comment on or otherwise explain it or assist
in its implmentation may be prepared, copied, published and distributed,
in whole or in part, without restriction of any kind, provided that the
above copyright notice and this paragraph are included on all such
copies and derivative works. However, this document itself may not be
modified in any way, such as by removing the copyright notice or
references to the Internet Society or other Internet organizations,
except as needed for the purpose of developing Internet standards in
which case the procedures for copyrights defined in the Internet
Standards process must be followed.
Wood Informational - December 22, 1999 14
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