Network Working Group J. Arvidsson
Request for Comments: 3067 Telia CERT
Category: Informational A. Cormack
JANET-CERT
Y. Demchenko
TERENA
J. Meijer
SURFnet
February 2001
TERENA's Incident Object Description and Exchange Format Requirements
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract
The purpose of the Incident Object Description and Exchange Format is
to define a common data format for the description, archiving and
exchange of information about incidents between CSIRTs (Computer
Security Incident Response Teams) (including alert, incident in
investigation, archiving, statistics, reporting, etc.). This
document describes the high-level requirements for such a description
and exchange format, including the reasons for those requirements.
Examples are used to illustrate the requirements where necessary.
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].
Arvidsson, et al. Informational [Page 1]
RFC 3067 IODEF Requirements February 2001
This document defines requirements for the Incident object
Description and Exchange Format (IODEF), which is the intended
product of the Incident Taxonomy Working Group (ITDWG) at TERENA [2].
IODEF is planned to be a standard format which allows CSIRTs to
exchange operational and statistical information; it may also provide
a basis for the development of compatible and inter-operable tools
for Incident recording, tracking and exchange.
Another aim is to extend the work of IETF IDWG (currently focused on
Intrusion Detection exchange format and communication protocol) to
the description of incidents as higher level elements in Network
Security. This will involve CSIRTs and their constituency related
issues.
The IODEF set of documents of which this document is the first will
contain IODEF Data Model and XML DTD specification. Further
discussion of this document will take place in the ITDWG mailing
lists <incident-taxonomy@terena.nl> or <iodef@terena.nl>, archives
are available correspondently at
http://hypermail.terena.nl/incident-taxonomy-list/mail-archive/ and
http://hypermail.terena.nl/iodef-list/mail-archive/
This work is based on attempts to establish cooperation and
information exchange between leading/advanced CSIRTs in Europe and
among the FIRST community. These CSIRTs understand the advantages of
information exchange and cooperation in processing, tracking and
investigating security incidents.
Computer Incidents are becoming distributed and International and
involve many CSIRTs across borders, languages and cultures. Post-
Incident information and statistics exchange is important for future
Incident prevention and Internet security improvement. The key
element for information exchange in all these cases is a common
format for Incident (Object) description.
It is probable that in further development or implementation the
IODEF might be used for forensic purposes, and this means that
Incident description must be unambiguous and allow for future custody
(archiving/documentation) features.
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Another issue that is targeted by developing IODEF is a need to have
higher level Incident description and exchange format than will be
provided by IDS (Intrusion Detection Systems) and the proposed IDEF
(Intrusion Detection Exchange Format). Compatibility with IDEF and
other related standards will be satisfied by the IODEF requirement on
modularity and extensibility. IODEF should vertically be compatible
with IDMEF, IODEF might be able to include or reference IDMEF Alert
message as initial information about Incident.
A definition of the main terms used in the rest of document is given
for clarity.
Where possible, existing definitions will be used; some definitions
will need additional detail and further consideration.
Taxonomy of the Computer Security Incident related terminology made
by TERENA's ITDWG [2] is presented in [12].
An assault on system security that derives from an intelligent
threat, i.e., an intelligent act that is a deliberate attempt
(especially in the sense of a method or technique) to evade security
services and violate the security policy of a system.
Attack can be active or passive, by insider or by outsider, or via
attack mediator.
Attacker is individual who attempts one or more attacks in order to
achieve an objective(s).
For the purpose of IODEF attacker is described by its network ID,
organisation which network/computer attack was originated and
physical location information (optional).
CSIRT (Computer Security Incident Response Team) is used in IODEF to
refer to the authority handling the Incident and creating Incident
Object Description. The CSIRT is also likely to be involved in
evidence collection and custody, incident remedy, etc.
In IODEF CSIRT represented by its ID, constituency, public key, etc.
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An intended or unintended consequence of an attack which affects the
normal operation of the targeted system or service. Description of
damage may include free text description of actual result of attack,
and, where possible, structured information about the particular
damaged system, subsystem or service.
An action directed at a target which is intended to result in a
change of state (status) of the target. From the point of view of
event origination, it can be defined as any observable occurrence in
a system or network which resulted in an alert being generated. For
example, three failed logins in 10 seconds might indicate a brute-
force login attack.
Evidence is information relating to an event that proves or supports
a conclusion about the event. With respect to security incidents (the
events), it may include but is not limited to: data dump created by
Intrusion Detection System (IDS), data from syslog file, kernel
statistics, cache, memory, temporary file system, or other data that
caused the alert or were collected after the incident happened.
Special rules and care must be taken when storing and archiving
evidence, particularly to preserve its integrity. When necessary
evidence should be stored encrypted.
According to the Guidelines for Evidence Collection and Archiving
(Evidence) evidence must be strictly secured. The chain of evidence
custody needs to be clearly documented.
It is essential that evidence should be collected, archived and
preserved according to local legislation.
An Incident is a security event that involves a security violation.
An incident can be defined as a single attack or a group of attacks
that can be distinguished from other attacks by the method of attack,
identity of attackers, victims, sites, objectives or timing, etc.
An incident is a root element of the IODEF. In the context of IODEF,
the term Incident is used to mean a Computer Security Incident or an
IT Security Incident.
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However we should distinguish between the generic definition of
'Incident' which is an event that might lead to damage or damage
which is not too serious, and 'Security Incident' and 'IT Security
Incident' which are defined below:
a) Security incident is an event that involves a security violation.
This may be an event that violates a security policy, UAP, laws
and jurisdictions, etc. A security incident may also be an
incident that has been escalated to a security incident.
A security incident is worse than an incident as it affects the
security of or in the organisation. A security incident may be
logical, physical or organisational, for example a computer
intrusion, loss of secrecy, information theft, fire or an alarm
that doesn't work properly. A security incident may be caused on
purpose or by accident. The latter may be if somebody forgets to
lock a door or forgets to activate an access list in a router.
b) An IT security incident is defined according to [9] as any real or
suspected adverse event in relation to the security of a computer
or computer network. Typical security incidents within the IT
area are: a computer intrusion, a denial-of-service attack,
information theft or data manipulation, etc.
Victim is individual or organisation which suffered the attack which
is described in incident report.
For the purpose of IODEF victim is described by its network ID,
organisation and location information.
A flaw or weakness in a system's design, implementation, or operation
and management that could be exploited to violate the system's
security policy.
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Most systems have vulnerabilities of some sort, but this does not
mean that the systems are too flawed to use. Not every threat
results in an attack, and not every attack succeeds. Success depends
on the degree of vulnerability, the strength of attacks, and the
effectiveness of any countermeasures in use. If the attacks needed
to exploit a vulnerability are very difficult to carry out, then the
vulnerability may be tolerable. If the perceived benefit to an
attacker is small, then even an easily exploited vulnerability may be
tolerable. However, if the attacks are well understood and easily
made, and if the vulnerable system is employed by a wide range of
users, then it is likely that there will be enough benefit for
someone to make an attack.
where possible.
Comment:
The IETF has already developed a number of standards in the areas of
networks and security that are actually deployed in present Internet.
Current standards provide framework for compatibility of IODEF with
other related technologies necessary to operate /implement IODEF in
practice. Another issue of compatibility for the IODEF is its
general compatibility with IDEF currently being developed by IETF
IDEWG. In the interest of time and compatibility, defined and
accepted standards should be used wherever possible.
In particularly, IODEF specification proposals SHOULD rely heavily on
existing communications, encryption and language standards, where
possible.
Comment:
Since some Incidents need involvement of CSIRTs from different
countries, cultural and geographic regions, the IODEF description
must be formatted such that they can be presented to an operator in a
local language and adhering to local presentation formats.
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Although metalanguage for IODEF identifiers and labels is considered
to be English, a local IODEF implementation might be capable to
translate metalanguage identifiers and labels into local language and
presentations if necessary.
Localized presentation of dates, time and names may also be required.
In cases where the messages contain text strings and names that need
characters other than Latin-1 (or ISO 8859-1), the information
preferably should be represented using the ISO/IEC IS 10646-1
character set and encoded using the UTF-8 transformation format, and
optionally using local character sets and encodings [13].
allow aggregation and filtering of data.
Comment:
It is suggested that Incident description with IODEF might include
external information, e.g., from IDS, or reference externally stored
evidence custody data, or such information might be removed from
current IODEF description, e.g., in purposes of privacy or security.
Another practical/real life motivation for this requirement is to
give possibility for some CSIRTs/managers to perform filtering and/or
data aggregation functions on IODEF descriptions for the purposes of
statistics, reporting and high level Incident information exchange
between CSIRTs and/or their constituency and sponsors.
Therefore the IODEF descriptions MUST be structured to facilitate
these operations. This also implies to strong IODEF semantics.
policy attribute to every element.
Comment:
IODEF Incident descriptions potentially contain sensitive or private
information (such as passwords, persons/organisations identifiers or
forensic information (evidence data)) and in some cases may be
exposed to non-authorised persons. Such situations may arise
particularly in case of Incident information exchange between CSIRTs
or other involved bodies. Some cases may be addressed by encrypting
IODEF elements, however this will not always be possible.
Therefore, to prevent accidental disclosure of sensitive data, parts
of the IODEF object must be marked with access restriction
attributes. These markings will be particularly useful when used
with automated processing systems.
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RFC 3067 IODEF Requirements February 2001
standard communication protocols, for example, e-mail, WWW/HTTP,
LDAP.
Comment:
IODEF description is normally created by a human using special or
standard text editors. The IODEF is targeted to be processed by
automated Incident handling systems but still must be human readable,
able to be viewed and browsed with standard tools (e.g., browsers or
electronic table processors or database tools like MS Excel or
Access). Incident information exchange will normally require
authorisation by an operator or CSIRT manager so is not expected to
be initiated automatically. The role of Incident handling system is
to provide assistance and tools for performing the exchange.
It is important to distinguish the purposes of the machine readable
and exchangeable IDEF Intrusion message format and the human oriented
and created IODEF Incident description.
Communications security requirements will be applied separately
according to local policy so are not defined by this document.
identification number (or identifier), IO purpose and default
permission level
Comment:
Unique identification number (or identifier) is necessary to
distinguish one Incident from another. It is suggested that unique
identification number will contain information at least about IO
creator, i.e. CSIRT or related body. The classification of the
Incident may also be used to form a unique identification number. IO
purpose will actually control which elements are included in the
IODEF object Purposes may include incident alert/registration,
handling, archiving, reporting or statistics. The purpose, incident
type or status of Incident investigation may require different levels
of access permission for the Incident information.
It is considered that root element of the IODEF will be <INCIDENT>
and additional information will be treated as attributes of the root
element.
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RFC 3067 IODEF Requirements February 2001
the attack if it is known.
It is expected that this type will be drawn from a standardized list
of events; a new type of event may use a temporary implementation-
specific type if the event type has not yet been standardized.
Comment:
Incident handling may involve many different staff members and teams.
It is therefore essential that common terms are used to describe
incidents.
If the event type has not yet been standardized, temporary type
definition might be given by team created IO. It is expected that
new type name will be self-explanatory and derived from a similar,
existing type definition.
advisories, such as those from CERT/CC, CVE, can be referenced.
Comment:
Using standard Advisories and lists of known Attacks and
Vulnerabilities will allow the use of their recommendations on
Incident handling/prevention. Such information might be included as
an attribute to the attack or vulnerability type definition.
caused the current Incident.
Comment:
Description of attack includes information about attacker and victim,
the appearance of the attack and possible impact. At the early stage
of Intrusion alert and Incident handling there is likely to be
minimal information, during handling of the Incident this will grow
to be sufficient for Incident investigation and remedy. Element
<ATTACK> should be one of the main elements of Incident description.
additional detailed data related to this specific underlying
event(s)/activity, often referred as evidence.
Comment:
For many purposes Incident description does not need many details on
specific event(s)/activity that caused the Incident; this information
may be referenced as external information (by means of URL). In some
cases it might be convenient to store separately evidence that has
different access permissions. It is foreseen that another standard
will be proposed for evidence custody [5].
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attacker and victim.
Comment:
This information is necessary to identify the source and target of
the attack. The minimum information about attacker and victim is
their IP or Internet addresses, extended information will identify
their organisations allowing CSIRTs to take appropriate measures for
their particular constituency.
different types of device addresses, e.g., IP address (version 4 or
6) and Internet name.
Comment:
The sites from which attack is launched might have addresses in
various levels of the network protocol hierarchy (e.g., Data layer 2
MAC addresses or Network layer 3 IP addresses). Additionally, the
devices involved in an intrusion event might use addresses that are
not IP-centric, e.g., ATM-addresses. It is also understood that
information about the source and target of the attack might be
obtained from IDS and include the IP address, MAC address or both.
Object (CSIRT or other authority). This may be the sender in an
information exchange or the team currently handling the incident.
Comment:
The identity of Incident description creator is often valuable
information for Incident response. In one possible scenario the
attack may progress through the network, comparison of corresponding
incidents reported by different authorities might provide some
additional information about the origin of the attack. This is also
useful information at post-incident information handling/exchange
stage.
possible impact of this event on the target. The value of this
field should be drawn from a standardized list of values if the
attack is recognized as known, or expressed in a free language by
responsible CSIRT team member.
Comment:
Information concerning the possible impact of the event on the target
system provides an indication of what the attacker is attempting to
do and is critical data for the CSIRTs to take actions and perform
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damage assessment. If no reference information (Advisories) is
available, this field may be filled in based on CSIRT team
experience.
It is expected that most CSIRTs will develop Incident handling
support systems, based on existing Advisories (such as those from
CERT/CC, CVE, etc.) that usually contain list of possible impacts for
identified attacks.
This also relates to the development of IDEF which will be
implemented in intelligent IDS, able to retrieve information from
standard databases of attacks and vulnerabilities [3].
the report information.
Comment:
Including this information is essential at the stage of Incident
creation, particularly in cases when intelligent automatic IDS or
expert systems are used. These normally use statistical engines to
estimate the event probability.
actions taken in the course of this incident by previous CSIRTs.
Comment:
The IODEF describes an Incident throughout its life-time from Alert
to closing and archiving. It is essential to track all actions taken
by all involved parties. This will help determine what further
action needs to be taken, if any. This is especially important in
case of Incident information exchange between CSIRTs in process of
investigation.
along Incident life-time.
Comment:
Time is important from both a reporting and correlation point of
view. Time is one of main components that can identify the same
Incident or attack if launched from many sites or distributed over
the network. Time is also essential to be able to track the life of
an Incident including Incident exchange between CSIRTs in process of
investigating.
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RFC 3067 IODEF Requirements February 2001
from UTC. (Note: See RFC 1902 for guidelines on reporting time.)
Comment:
For event correlation purposes, it is important that the manager be
able to normalize the time information reported in the IODEF
descriptions.
current standards for Year 2000 rollover, and it must have
sufficient capability to continue reporting date values past the
year 2038.
Comment:
It is stated in the purposes of the IODEF that the IODEF shall
describe the Incident throughout its life-time. In the case of
archiving this duration might be unlimited. Therefore,
implementations that limit expression of time value (such as 2038
date representation limitation in "Unix time") MUST be avoided.
by the IODEF.
Comment:
The time data may be included into IODEF description by existing
information systems, retrieved from incident reporting messages or
taken from IDS data or other event registration tools. Each of these
cases may have its own different time granularity. For the purposes
of implementation, it should be possible to handle time at different
stages according to the local system capabilities.
content.
The selected design should be capable of supporting a variety of
encryption algorithms and must be adaptable to a wide variety of
environments.
Comment:
IODEF Incident descriptions potentially contain sensitive or private
information (such as forensic data (evidence data), passwords, or
persons/organisations identifiers) which would be of great interest
to an attacker or malefactor. Incident information normally will be
stored on a networked computer, which potentially may be exposed to
attacks (or compromised). Incident information may be transmitted
across uncontrolled network segments. Therefore, it is important
that the content be protected from unauthorised access and
modification. Furthermore, since the legal environment for privacy
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RFC 3067 IODEF Requirements February 2001
and encryption technologies are varied from regions and countries and
change 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. Additional measures may be
undertaken for securing the Incident during communication but this
issue is outside of IODEF scope as it implies more strict rules for
IO archiving and storing in general.
content.
The selected design should be capable of supporting a variety of
integrity mechanisms and must be adaptable to a wide variety of
environments.
Comment:
Special measures should be undertaken to prevent malicious IO
changes.
Additional measures may be undertaken for securing the Incident
during communication but this issue is outside of IODEF scope.
of the message content.
Comment:
Authenticity and accountability is needed by many teams, especially
given the desire to automatically handle IOs, therefore it MUST be
included in the IODEF. Because of the importance of IO authenticity
and non-repudiation to many teams and especially in case of
communication between them, the implementation of these requirements
is strongly RECOMMENDED.
which may be used by implementers. This allows future
implementation-specific or experimental data. The implementer
MUST indicate how to interpret any included extensions.
Comment:
Implementers might wish to supply extra data such as information for
internal purposes or necessary for the particular implementation of
their Incident handling system. These data may be removed or not in
external communications but it is essential to mark them as
additional to prevent wrong interpretation by different systems.
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Comment:
IODEF is a human oriented format for Incident description, and IODEF
description should be capable of being read by humans. The use of
automatic parsing tools is foreseen but should not be critically
necessary. Therefore, IODEF must provide good semantics, which will
be key to understanding what the description contains. In some
cases the IODEF description will be used for automatic decision
making, so it is important that the description be interpreted
correctly. This is an argument for using language-based semantics.
The metalanguage for IODEF identifiers and labels is proposed to be
English, a local IODEF implementation might be able to translate
metalanguage identifiers and labels into local language and
presentations if necessary.
the use of new technologies and development of automated Incident
handling system demands extension of IODEF, the IODEF will be
capable to include new information.
Comment:
In addition to the need to extend IODEF to support new Incident
handling tools, it is also suggested that IODEF will incorporate new
developments from related standardisation areas such as IDEF for IDS
or the development of special format for evidence custody. The
procedure for extension should be based on CSIRT/IODEF community
acceptance/approval.
This memo describes requirements to an Incident Object Description
and Exchange Format, which intends to define a common data format for
the description, archiving and exchange of information about
incidents between CSIRTs (including alert, incident in investigation,
archiving, statistics, reporting, etc.). In that respect the
implementation of the IODEF is a subject to security considerations.
Particular security requirement to access restriction indication is
discussed in section 4.3, requirements to Incident description
confidentiality, integrity, authenticity and non-repudiation are
described in sections 6.16, 6.17, 6.18.
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[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Incident Taxonomy and Description Working Group Charter -
http://www.terena.nl/task-forces/tf-csirt/i-taxonomy/
[3] Intrusion Detection Exchange Format Requirements by Wood, M. -
December 2000, Work in Progress.
[4] Intrusion Detection Message Exchange Format Extensible Markup
Language (XML) Document Type Definition by D. Curry, H. Debar -
February 2001, Work in Progress.
[5] Guidelines for Evidence Collection and Archiving by Dominique
Brezinski, Tom Killalea - July 2000, Work in Progress.
[6] Brownlee, N. and E. Guttman, "Expectations for Computer Security
Incident Response", BCP 21, RFC 2350, June 1998.
[7] Shirey, R., "Internet Security Glossary", FYI 36, RFC 2828, May
2000.
[8] Establishing a Computer Security Incident Response Capability
(CSIRC). NIST Special Publication 800-3, November, 1991
[9] Handbook for Computer Security Incident Response Teams (CSIRTs),
Moira J. West-Brown, Don Stikvoort, Klaus-Peter Kossakowski. -
CMU/SEI-98-HB-001. - Pittsburgh, PA: Carnegie Mellon University,
1998.
[10] A Common Language for Computer Security Incidents by John D.
Howard and Thomas A. Longstaff. - Sandia Report: SAND98-8667,
Sandia National Laboratories -
http://www.cert.org/research/taxonomy_988667.pdf
[11] Best Current Practice of incident classification and reporting
schemes currently used by active CSIRTs. -
http://www.terena.nl/task-forces/tf-csirt/i-
taxonomy/docs/BCPreport1.rtf
[12] Taxonomy of the Computer Security Incident related terminology -
http://www.terena.nl/task-forces/tf-csirt/i-taxonomy/docs/i-
taxonomy_terms.html
[13] Multilingual Support in Internet/IT Applications. -
http://www.terena.nl/projects/multiling/
Arvidsson, et al. Informational [Page 15]
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Acknowledgements:
This document was discussed at the Incident Taxonomy and Description
Working Group seminars (http://www.terena.nl/task-forces/tf-
csirt/tf-csirt000929prg.html#itdwg) in the frame of TERENA Task Force
TF-CSIRT (http://www.terena.nl/task-forces/tf-csirt/). Incident
Taxonomy and Description Working Group at TERENA can be contacted via
the mailing lists <incident-taxonomy@terena.nl> or <iodef@terena.nl>,
archives are available correspondently at
http://hypermail.terena.nl/incident-taxonomy-list/mail-archive/ and
http://hypermail.terena.nl/iodef-list/mail-archive/
Authors' Addresses
Jimmy Arvidsson
Telia CERT
EMail: Jimmy.J.Arvidsson@telia.se
Andrew Cormack
JANET-CERT
EMail: Andrew.Cormack@ukerna.ac.uk
Yuri Demchenko
TERENA
EMail: demch@terena.nl
Jan Meijer
SURFnet
EMail: jan.meijer@surfnet.nl
Arvidsson, et al. Informational [Page 16]
RFC 3067 IODEF Requirements February 2001
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