INTERNET-DRAFT Adam W. Montville
Intended Status: Standards Track (Tripwire)
Updates: 5070 (if approved) David Black
Expires: December 22, 2014 (EMC)
June 20, 2014
IODEF Enumeration Reference Format
draft-ietf-mile-enum-reference-format-06
Abstract
The Incident Object Description Exchange Format (IODEF) provides a
Reference class used to reference external entities (such as
enumeration identifiers). However, the method of external entity
identification has been left unstructured. This document describes a
method to provide structure for referencing external entities for the
IODEF Reference class and thus updates IODEF's ReferenceName
(RFC5070).
Status of this Memo
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Copyright and License Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
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document authors. All rights reserved.
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Table of Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Referencing External Enumerations . . . . . . . . . . . . . . 3
3 Security Considerations . . . . . . . . . . . . . . . . . . . . 5
4 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
5 IODEF XML Schema Changes . . . . . . . . . . . . . . . . . . . . 6
6 References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1 Normative References . . . . . . . . . . . . . . . . . . . 8
6.2 Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1 Introduction
There is an identified need to specify a format to include relevant
enumeration values in an IODEF document. It is anticipated that this
requirement will exist in other standardization efforts within
several IETF Working Groups, but the scope of this document pertains
solely to IODEF [IODEF].
1.1 Terminology
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 [RFC2119].
2. Referencing External Enumerations
The need is to place enumeration identifiers and their references in
IODEF [IODEF]'s Reference class. There are several ways to
accomplish this goal, but the most appropriate at this point is to
require a specific format for the ReferenceName string of the IODEF
[IODEF] Reference class, and use an IANA registry to manage the
resulting reference formats.
+------------------+
| Reference |
+------------------+
| |<>----------[ ReferenceName ]
| |<>--{0..*}--[ URL ]
| |<>--{0..*}--[ Description ]
+------------------+
FIGURE 1: IODEF [IODEF] Reference Class
Per IODEF [IODEF] the ReferenceName is of type ML_STRING. This
becomes problematic when specific references, especially enumerations
such as CVE [CVE], CCE [CCE], CPE [CPE] and so on, are referenced -
how is an implementer to know which type of reference this is, and
thus how to parse it? One solution, presented here, is to require
that ReferenceName follow a particular format.
Inclusion of such enumerations, especially those related to security
automation, is important to incident communication and investigation.
Typically, an enumeration identifier is simply an identifier with a
specific format as defined by an external party.
2.1 Reference Name Format
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The Reference Name Format uses XML to provide the structure for
enumeration identification, and requires that a specific Index be
associated with the ID. An implementer can look up the ID type (as
referenced by the Index) in the IANA table (see Section 4) to
understand how the ID is structured. The Index field in the XML
unambiguously indicates which IANA registry entry is to be used to
correctly reference the enumeration specification, which avoids
interpretation of version strings that may have specification-
specific formats.
1
CXI-1234-XYZ
http://cxi.example.com
Foo
LISTING 1: Example Use of IODEF Enumeration Reference Format
Information in the IANA table (see Section 4) would include:
Full Name: Concept X Identifier
Index: 1
Version: any
Specification URI: http://cxi.example.com/spec_url
2.3 Reference Method Applicability
While the scope of this document pertains to IODEF [IODEF], it
should be readily apparent that any standard needing to reference
an enumeration identified by a specially formatted string can use
this method of providing structure after the standard has been
published. In effect, this method provides a standardized
interface for enumerations, thus allowing a loose coupling between
a given standard and the enumeration identifiers it needs to
reference now and in the future.
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3 Security Considerations
Producers of IODEF [IODEF] content SHOULD be careful to ensure a
proper mapping of enumeration reference ID elements to the correct
Index. Potential consequences of not mapping correctly include
inaccurate information references and similar distribution of
misinformation.
Use of enumeration reference IDs from trusted sources SHOULD be
preferred by implementers to mitigate the risk of receiving and/or
providing misinformation. Trust decisions with respect to
enumeration reference providers is beyond the scope of this
document.
In some cases it might be possible for a third-party to host
content associated with an enumeration reference ID. In such a
circumstance, trust SHOULD extend from the origin of the
enumeration reference ID to the third-party, effectively making
the third-party a trusted third-party in the context of providing
a particular set of enumeration reference IDs.
4 IANA Considerations
This document specifies an identifier format for the IODEF [IODEF]
ReferenceName string of the Reference class.
This memo creates the following registry for IANA to manage:
Name of the Registry: "Enumeration Reference Type Identifiers"
Fields to record in the registry:
Full Name: The full name of the enumeration as a string from
the printable ASCII character set.
Abbreviation: An abbreviation may be an acronym - it consists
of upper-case characters (at least two, upper-case is used to
avoid mismatches due to case differences), as specified by this
ABNF [RFC5234] syntax:
ABBREVIATION = 2*UC-ALPHA ; At least two
UC-ALPHA = %x41-5A ; A-Z
Multiple registrations MAY use the same Abbreviation but
MUST have different Versions.
Index: This is an IANA-assigned positive integer that
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identifies the registration. The first entry added to this
registry uses the value 1, and this value is incremented for
each subsequent entry added to the registry.
Version: The version of the enumeration as a free-form string
from the printable ASCII character set excepting white space.
Specification URI: A list of one or more URIs [RFC3986] from
which the registered specification can be obtained. The
registered specification MUST be readily and publicly available
from that URI. The URI SHOULD be a stable reference to a
specific version of the specification. URIs that designate the
latest version of a specification (which changes when a new
version appears) SHOULD NOT be used.
Initial registry contents: None.
Allocation Policy: Specification Required [RFC5226] (which implies
Expert Review [RFC5226]).
The Designated Expert is expected to consult with the MILE (Managed
Incident Lightweight Exchange) working group or its successor if any
such WG exists (e.g., via email to the working group's mailing list).
The Designated Expert is expected to review the request and validate
the appropriateness of the enumeration for the attribute. If a
specification is associated with the request, it MUST be reviewed by
the Designated Expert.
The Designated Expert is expected to ensure that the Full Name,
Abbreviation and Version are appropriate and that the information at
the Specification URI is sufficient to unambiguously parse
identifiers based on that specification. Additionally, the Designated
Expert should prefer short Abbreviations over long ones.
5 IODEF XML Schema Changes
The changes to the IODEF [IODEF] schema are detailed below. Note
that in addition to the element changes described below, certain
attributes of the xs:schema element in the schema document should be
updated, as well as certain information in the document class.
The xs:schema attributes are updated as follows:
targetNamespace="urn:ietf:params:xml:ns:iodef-1.01"
xmlns="urn:ietf:params:xml:ns:iodef-1.01"
xmlns:iodef="urn:ietf:params:xml:ns:iodef-1.01"
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The IODEF-Document element description is updated to have a fixed
version of "1.01" instead of "1.00", such that:
Is changed to:
The ReferenceName element is updated by replacing the following line
in the 1.00 schema:
With:
LISTING 2: IODEF Enumeration Reference Format Schema Changes
This change to the IODEF [IODEF] schema may cause interoperability
issues depending on tool implementation. If strict schema validation
is used by a 1.00 tool when parsing an incoming IODEF [IODEF] 1.01
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document, the elements under ReferenceName may not be understood and
could cause errors. If strict schema validation is not used when
parsing an incoming IODEF [IODEF] 1.01 document with a 1.00 tool, the
elements under ReferenceName should simply be present in the object
model, but this may lead to unpredictable results.
Implementers are encouraged to update their code to handle the IODEF
[IODEF] 1.00 schema and the 1.01 schemas explicitly to avoid any
unhandled exceptions that may occur when a 1.00 implementation
attempts to parse a 1.01 document.
6 References
6.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[IODEF] Danyliw, R., Meijer, J., and Y. Demchenko, "The Incident
Object Description Exchange Format", RFC 5070, December
2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for
Syntax Specifications: ABNF", STD 68, RFC 5234, January
2008.
6.2 Informative References
[CCE] http://cce.mitre.org
[CPE] http://cpe.mitre.org
[CVE] http://cve.mitre.org
Authors' Addresses
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Adam W. Montville
EMail: adam@stoicsecurity.com
David Black
EMC Corporation
EMail: david.black@emc.com
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