| MILE Working Group | J. Field |
| Internet-Draft | Pivotal |
| Intended status: Informational | S. Banghart |
| Expires: January 9, 2017 | D. Waltermire |
| NIST | |
| July 8, 2016 |
Resource-Oriented Lightweight Information Exchange
draft-ietf-mile-rolie-03
This document defines a resource-oriented approach for security automation information publication, discovery, and sharing. Using this approach, producers may publish, share and exchange representations of security incidents, attack indicators, software vulnerabilities, configuration checklists, and other security automation information as Web-addressable resources. Furthermore, consumers and other stakeholders may access and search this security information as needed, establishing a rapid and on-demand information exchange network for restricted internal use or public access repositories. This specification extends the Atom Publishing Protocol and Atom Syndication Format to transport and share security automation resource representations.
The source for this draft is being maintained in GitHub. Suggested changes should be submitted as pull requests at <https://github.com/CISecurity/ROLIE>. Instructions are on that page as well. Editorial changes can be managed in GitHub, but any substantial issues need to be discussed on the MILE mailing list.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on January 9, 2017.
Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
This document defines a resource-oriented approach to security automation information sharing that follows the REST [REST] architectural style. In this approach, computer security resources are maintained in web-accessible repositories structured as Atom Syndication Format [RFC4287] feeds. Representations of specific types of security automation information are categorized and organized into indexed collections, which may be requested by the consumer. As the set of resource collections are forward facing, the consumer may search all available content for which they are authorized to view, and request the information resources which are desired. Through use of granular authentication and access controls, only authorized consumers may be permitted the ability to read or write to a given feed. This approach is in contrast to, and meant to improve on, the traditional point-to-point messaging system, in which consumers must request individual pieces of information from a server following a triggering event. The point-to-point approach creates a closed system of information sharing that encourages duplication of effort and hinders automated security systems.
The goal of this document is to define a RESTful approach to security information communication with two primary intents: 1) increasing communication and sharing of incident reports, vulnerability assessments, configuration checklists, and other security automation information between providers and consumers; and 2) establishing a standardized communication system to support automated computer security systems.
In order to deal with the great variety in security automation information types and associated resource representations, this specification defines extension points that can be used to add support for new information types and associated resource representations by means of additional supplementary specification documents. This primary document is resource representation agnostic, and defines the core requirements of all implementations. Those seeking to provide support for specific security automation information types should refer to the specification for that format described by the IANA registry found in section 10.3.
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 [RFC2119].
Definitions for some of the common computer security-related terminology used in this document can be found in Section 2 of [RFC5070].
This specification uses XML Namespaces [W3C.REC-xml-names-20091208] to uniquely identify XML element names. It uses the following namespace prefix mappings for the indicated namespace URI:
Some sections of this specification are illustrated with fragments of a non-normative RELAX NG Compact schema [relax-NG]. However, the text of this specification provides the definition of conformance. Complete schemas appear for the "urn:ietf:params:xml:ns:rolie-1.0" namespace in appendix C. Schema for the "http://www.w3.org/2007/app" and "http://www.w3.org/2005/Atom" namespaces appear in RFC5023 appendix B [RFC5023] and RFC4287 appendix B [RFC4287] respectively.
It is well known thatthreats to computer security are evolving ever more rapidly as time goes on. As software increases in complexity, the number of vulnerabilities in systems and networks can increase exponentially. Threat actors looking to exploit these vulnerabilities are making more frequent and more widely distributed attacks across a large variety of systems. The adoption of liberal information sharing amongst attackers creates a window of as little as a few hours between the discovery of a vulnerability and attacks on a vulnerable system. As the skills and knowledge required to identify and combat these attacks become more and more specialized, even a well established and secure system may find itself unable to quickly respond to an incident. Effective identification of and response to a sophisticated attack requires open cooperation and collaboration between defending operators, software vendors, and end-users. To improve the timeliness of responses, automation must be used to acquire, contextualize, and put to use shared computer security information.
Existing approaches to computer security information sharing often use message exchange patterns that are point-to-point, and event-driven. Sometimes, information that may be useful to share with multiple peers is only made available to peers after they have specifically requested it. Unfortunately, a sharing peer may not know, a priori, what information to request from another peer. Some exsisting systems provide a mechanism for unsolicited information requests, however these reports are again sent point-to-point, and must be reviewed for relevance and then prioritized for action by the recipient, introducing additional latency.
In order to adequately combat evolving threats, computer security information resource providers should be enabled to share selected information proactively as appropriate. Proactive sharing greatly aids knowledge dissemination, and improves response times and usability.
For example, a security analyst can benefit by having the ability to search a comprehensive collection of attack indicators that have been published by a government agency, or by another member of a sharing consortium. The representation of each indicator may include links to the related resources, enabling an appropriately authenticated and authorized analyst to freely navigate the information space of indicators, incidents, vulnerabilities, and other computer security domain concepts as needed. In this way, an analyst can more effectively utilize the super set of information made publicly available.
Consider also the case of an automated endpoint management system attempting to proactively prevent software flaws from compromising the security of the affected systems. During its full network sweep, the endpoint monitoring system would check each endpoint for outdated or vulnerable software. This system would benefit from having access to not only the software vendor's list of vulnerabilities, but also vulnerabilities discovered by other vulnerability researchers. An advanced system could even give back to this sharing consortium by sharing any vulnerabilities that it discovers. The natural conclusion of such a sharing network is an automated security solution that can dynamically find and collect information from a globally distributed web of information repositories.
The following section discusses additional specific technical issues that motivated the development of this alternative approach.
The existing approaches to computer security information sharing are based upon message-oriented interactions. The following paragraphs explore some of the architectural constraints associated with message-oriented interactions and consider the relative merits of an alternative model based on a resource-oriented architecture for use in some use case scenarios.
ROLIE specifies a resource-oriented architecture that attempts to address the issues present in a message-oriented architecture.
In general, message-based integration architectures may be based upon either an RPC-style or a document-style binding. The message types defined by Real-time Inter-network Defense (RID) [RFC6545] represents an example of an RPC-style request. This approach imposes implied requirements for conversational state management on both of the communicating RID endpoint(s). Experience has shown that this state management frequently becomes the limiting factor with respect to the runtime scalability of an RPC-style architecture.
In addition, the practical scalability of a peer-to-peer message-based approach will be limited by the administrative procedures required to manage O(N^2) trust relationships and at least O(N) policy groups.
As long as the number of participating entities in an information sharing consortium is limited to a relatively small number of nodes (i.e., O(2^N), where N < 5), these scalability constraints may not represent a critical concern. However, when there is a requirement to support a significantly larger number of participating peers, a different architectural approach will be required. Towards the goal to create a large-scale network of entities sharing information, this traditional architecture only creates small and isolated groupings of sharing, encouraging effort duplication between these sharing islands. One alternative to the message-based approach that has demonstrated scalability and a high degree of connectedness is the REST [REST] architectural style.
Applying the REST architectural style to the problem domain of security information sharing involves exposing information in any relevant type as simple Web-addressable resources. Each provider maintains their own repository of data, with public and private sections as needed. Any producer or consumer can then discover these repositories, search for relevant feeds, and pull information from them. By using this approach, an organization can more quickly and easily share relevant data representations with a much larger and potentially more diverse constituency. A consumer may leverage virtually any available HTTP user agent in order to make requests of the service provider. This improved ease of use enables more rapid adoption and broader participation, thereby improving security for everyone.
A key aspect of any RESTful Web service is the ability provide multiple resource representations. For example, clients may request that a given resource representation be returned as XML, JSON, or in some other format. In order to enable backwards-compatibility and interoperability with existing implementations, the RESTful approach allows the provider to make differing formats available proactively, allowing the consumer to simply select the version that best suits them.
Finally, an important principle of the REST architectural style is the focus on hypermedia as the engine of application state (HATEOAS). Rather than the server maintaining conversational state for each client, the server will instead include a suitable set of hyperlinks in the resource representation that is returned to the client. The included hyperlinks provide the client with a specific set of permitted state transitions. Using these links the client may perform an operation, such as updating or deleting the resource representation. The client may also be provided with hypertext links that can be used to navigate to any related resource. For example, the resource representation for an incident object may contain links to the related indicator resource(s). In this way, the server remains stateless with respect to a series of client requests.
In this section we consider an example scenario for creating a computer security "mashup".
A producer creates and maintains a feed of information on threat actors, whilst another creates and maintains a feed of attack indicators. Each has authorized a large consortium of security analysts to access these feeds as they see fit. Any one of these analysts can then make HTTP(s) requests to the servers to collect sets of information from each provider. The resulting correlations may yield new insights that enable a more timely and effective defensive response. Of course, this report may, in turn, be made available to others as a new Web-addressable resource, reachable via another URL. By exposing information using the RESTful approach in this way, the effectiveness of the collaboration amongst a consortium of cyber security stakeholders can be greatly improved.
This specification defines a profile of the Atom Publishing Protocol (AtomPub) [RFC5023] and Atom Syndication Format [RFC4287] providing implementation requirements for a security information sharing solution as a RESTful Web service.
This document assumes that the reader has an understanding of both the AtomPub and Atom Syndication Format specifications.
The following two sections of this document provide requirements for using the Atom Syndication Format and AtomPub as a RESTful binding for security automation information sharing.
This section describes a number of restrictions of and extensions to the Atom Publishing Protocol (AtomPub) [RFC5023] that define the use of that protocol in the context of a ROLIE-based solution.
As described in RFC5023 section 8 [RFC5023], a Service Document is an XML-based document format that allows a client to dynamically discover the collections provided by a publisher. A Service Document consists of one or more app:workspace elements that may each contain a number of app:collection elements.
The general structure of a service document is as follows (from RFC5023 section 4.2 [RFC5023]):
Service
o- Workspace
| |
| o- Collection
| |
| o- IRI, categories, media types
|
o- Workspace
|
o- Collection
|
o- IRI, categories, media types
In AtomPub, a Workspace, represented by the "app:workspace" element, describes a group of one or more Collections. Building on the AtomPub concept of a Workspace, in ROLIE a Workspace represents an aggregation of Collections pertaining to security automation information resources. This specification does not impose any restrictions on the number of Workspaces that may be in a Service Document or the specific Collections to be provided within a given Workspace.
The following restrictions are imposed on the use of the app:workspace element in ROLIE:
In AtomPub, a Collection in a Service Document, represented by the "app:collection" element, provides metadata that can be used to point to a specific Atom Feed that contains information Entries that may be of interest to a client. The association between a Collection and a Feed is provided by the "href" attribute of the app:collection element. Building on the AtomPub concept of a Collection, in ROLIE a Collection represents a pointer to a group of security automation information resources pertaining to a given type of security automation information. Collections are represented as Atom feeds as per RFC 5023. Feed specific requirements are defined in section 6.1.
The following restrictions are imposed on the use of the app:collection element for ROLIE:
This specification requires that an implementation MUST publish an Atom Service Document that describes the set of security information sharing collections that are provided by the repository.
The service document SHOULD be discoverable via the organization's Web home page or another well-known public resource. An example of this can be found in appendix A.1.
The service document SHOULD (TODO: MUST?) be located at the standardized location "https://{host:port}/rolie/servicedocument", where {host:port} is the authority portion of the URI. Dereferencing this URI MAY result in a redirect based on a HTTP 3xx status code to direct the client to the actual service document. This allows clients to have a well-known location to find a ROLIE service document, while giving implmentations flexibility over how the service is deployed.
When deploying a service document for use by a closed consortium, the service document MAY also be digitally signed and/or encrypted.
Implementations MUST support server-authenticated TLS.
Implementations MAY support mutually authenticated TLS.
Implementations MAY support client authenticated TLS.
Implementations MUST support user authentication. User authentication MAY be enabled for specific feeds.
Implementations MAY support more than one client authentication method.
Servers participating in an information sharing consortium and supporting interactive user logins by members of the consortium SHOULD support client authentication via a federated identity scheme as per SAML 2.0.
This document does not mandate the use of any specific user authorization mechanisms. However, service implementers SHOULD provide appropriate authorization checking for all resource accesses, including individual Atom Entries, Atom Feeds, and Atom Service Documents.
Authorization for a resource MAY be adjudicated based on the value(s) of the associated Atom <category> element(s).
The "/" resource MAY be provided for compatibility with existing deployments that are using Transport of Real-time Inter-network Defense (RID) Messages over HTTP/TLS [RFC6546]. Consistent with RFC6546 errata, a client requesting a GET on "/" MUST receive an HTTP status code 405 Method Not Allowed. An implementation MAY provide full support for RFC6546 such that a POST to "/" containing a recognized RID message type just works. Alternatively, a client requesting a POST to "/" MAY receive an HTTP status code 307 Temporary Redirect. In this case, the location header in the HTTP response will provide the URL of the appropriate RID endpoint, and the client may repeat the POST method at the indicated location. This resource could also leverage the new draft by reschke that proposes HTTP status code 308 (cf: draft-reschke-http-status-308-07.txt). TODO
Clients MUST be capable of recognizing and processing any standard HTTP status code, as defined in [RFC5023] Section 5
This section describes a number of restrictions of and extensions to the Atom Syndication Format [RFC4287] that define the use of that format in the context of a ROLIE-based solution.
As described in RFC4287 section 4.1.1 [RFC4287], an Atom Feed is an XML-based document format that describes a list of related information items, also known as a collection. Each Feed document, represented using the atom:feed element, contains a collection of zero or more related information items individually called a "member entry" or "entry".
When applied to the problem domain of security automation information sharing, an Atom Feed may be used to represent any meaningful collection of security automation information resources including a set of configuration checklists or software vulnerabilities. Each entry in an atom:feed represents an individual resource, such as a specific checklist or software vulnerability record. Additional Feeds can be used to represent collections of other meaningful and useful security automation resources.
This Atom feed definition represents a stricter definition of the Atom entry element. Any element not specified here inherits its definition and requirements from RFC 4287.
atomFeed =
element atom:feed {
atomCommonAttributes,
(atomAuthor*
& atomCategory+
& atomContributor*
& atomGenerator?
& atomIcon?
& atomId
& atomLink*
& atomLogo?
& atomRights?
& atomSubtitle?
& atomTitle
& atomUpdated
& extensionElement*),
atomEntry*
}
An atom:feed may be categorized and may contain information from zero or more categories. In Atom the naming scheme and the semantic meaning of the terms used to identify an Atom category are application-defined.
The following restrictions are imposed on the use of the atom:category element when used in a ROLIE atom:feed:
Link relations defined by the atom:link element are used to represent state transitions using a stateless approach. In Atom a type of link relationship can be defined using the "rel" attribute. The following are link relations that provide state transitions related to a ROLIE Atom feed.
An atom:feed MAY include additional link relationships not specified in this document. If a client encounters an unknown link relationship type, the client MUST ignore the unrecognized link and continue processing the remaining resource representation as if the unrecognized link element did not appear.
The Feed Paging and Archiving [RFC5005] Atom extension provides capabilities for paging and archiving of feeds.
A atom:feed can contain an arbitrary number of entries. In some cases, a complete feed may consist of a large number of entries. Additionally, as new and updated entries are ordered at the beginning of a feed, a client may only be interested in retriving the first X entries in a feed to process only the entries that have changed since the last access to a ROLIE repository feed. As a practical matter, the full result set will likely need to be divided into more manageable portions. Based on RFC5005 section 3 [RFC5005], the links SHOULD be included in all feeds to support paging using the following link relation types:
For example:
<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">
<title>Paged Feed</title>
<link rel="self" href="http://example.org/feedA?page=5"/>
<link rel="first" href="http://example.org/feedA?page=1"/>
<link rel="prev" href="http://example.org/feedA?page=4"/>
<link rel="next" href="http://example.org/feedA?page=6"/>
<link rel="last" href="http://example.org/feedA?page=10"/>
<updated>2012-05-04T18:13:51.0Z</updated>
<!-- remainder of feed elements -->
</feed>
Example Paged Feed
An historical feed may need to be stable, and/or divided into some defined epochs. Implementations SHOULD support the mechanisms described in RFC5005 section 4 [RFC5005] to provide capabilities for maintaining archiving of feeds.
The atom:updated element MUST be populated with the current time at the instant the feed representation was last updated by adding, updating, or deleting an entry; or changing any metadata for the feed.
Each entry in an Atom feed, represented by the atom:entry element, describes a single information record, format, and type combination. The following atom:entry schema definition represents a stricter representation of the atom:entry element defined in RFC 4287 for use in a ROLE-based Atom Feed.
atomEntry =
element atom:entry {
atomCommonAttributes,
(atomAuthor*
& atomCategory*
& atomContent
& atomContributor*
& atomId
& atomLink*
& atomPublished?
& atomRights?
& atomSource?
& atomSummary?
& atomTitle
& atomUpdated
& rolieFormat
& extensionElement*)
}
There MUST be exactly one atomContent element in the entry. The content element MUST adhere to this definition:
atomContent =
element atom:content {
atomCommonAttributes,
attribute type { atomMediaType },
attribute src { atomUri },
empty
}
The type attribute MUST be the serialization type of the content, for example, XML or JSON. The src attribute is a link to the payload.
There MAY be zero or more atom:link elements in the entry. The content element MUST adhere to this definition:
The link element follows the definition laid out in the Atom Syndication Document.
If there entries with the same format and category but a different type, it MUST be linked to using the "alternate" link relation.
There MUST be exactly one rolie:format element in the Entry. This format SHOULD be one of the formats listed under the category of this entry as discussed in the and Content Model section. The format is contained in the content of this tag.
In addition to the standard Link Relations defined by the Atom specification, this specification defines the following additional Link Relation terms, which are introduced specifically in support of the Resource-Oriented Lightweight Information Exchange protocol.
TODO: This section needs to be expanded.
Implementers MUST support OpenSearch 1.1 [opensearch] as the mechanism for describing how clients may form search requests.
Implementers MUST provide a link with a relationship type of "search". This link SHALL return an Open Search Description Document as defined in OpenSearch 1.1.
Implementers MUST fully qualify all OpenSearch URL template parameter names using the defined XML namespaces, as appropriate.
This specification does not require a particular security automation information type or content format; rather, it provides extension points using IANA tables to allow for future extensions of supported information types and formats.
A given security automation information type is respresented using the "atom:category" element. In this way, an "atom:category" element can be used to:
As mentioned earlier, a key goal of this specification is to allow a consumer to identify security automation information resources of interest, and then choose a suitable format of the information to retrieve. For a given type of security automation information, it is expected that a number of different formats may be used to represent this information. To support this use case, both the serialization format and the specific data model expressed in that format must be known by the consumer.
The following sections describe how information types are defined and used, and how specific content formats are declared in ROLIE.
A security automation information type represents a class of information that represents the same or similar information model [RFC3444]. Notional examples of information types include:
This is a short list to inspire thought on possible information types, which will also include other information used to automate security processes.
This document does not specific any information types. Instead, information types in ROLIE are expected to be defined in extension documents that describe one or more new information types. This allows the information types used by ROLIE implementations to grow over time to support new security automation use cases. These extension documents may also enhance ROLIE resource representations by defining link relations, categories, and other AtomPub and Atom Syndication Format data model extensions to address the representational needs of specific information types. New information types are added to ROLIE through registrations to the IANA Security Resource Information Type registry defined in section 10.3.
The core extension point within this specification is the ability to define different security automation information types, which can be used to characterize the type of information contained in a ROLIE resource collection. The information type of a resource collection is characterized using an "atom:category" element with a "scheme" attribute value of "urn:ietf:params:rolie:information-type", and a "term" attribute value identifying the specific information type declared.
For example, the security automation information type "incident" would be identified as follows:
The Uniform Resource Name (URN) [RFC2141] "urn:ietf:params:rolie:information-type" is registered with IANA as described in section 10.2.
Registered security automation information type values are defined in the IANA table described in section 10.3.
A given information type may have a number of supported formats. Each format is expected to have a specification that defines the data model for the format. As described in section 6.2.3, the "rolie:format" element is used to describe the specific data model used to represent the resource referenced by a given "atom:entry". By declaring the data model used in this way, a consumer can choose to download or ignore the resource, or look for alternate formats. This saves the consumer from downloading and parsing resources that the consumer is not interested in or resources expressed in formats that are not understandable by the consumer.
TODO: Need to describe the structure and use of the rolie:format element.
TODO: define a schema for the "rolie:format" element.
This document defines a resource-oriented approach to security information sharing, where such information may include a variety of security resource categories, such as software identifiers (e.g. tags), incident reports, configuration assessment guidance, vulnerability assessment guidance, and so on.
TODO: Complete registration request specifics.
This document uses URNs to describe XML namespaces and XML schemas conforming to a registry mechanism described in [RFC3688].
ROLIE uses URNs to represent category schemes. This section creates and registers an IETF URN sub-namespace for use in ROLIE specifications and future extensions.
TODO: Add entry for: "urn:ietf:params:rolie:category:information-type"
This document creates the following registry for IANA to manage:
The Designated Expert is expected to consult with the MILE (Managed Incident Lightweight Exchange) working group or is 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 name, description, and associated specifications for the security resource category.
This document defines a resource-oriented approach to lightweight information exchange using HTTP, TLS, Atom Syndicate Format, and Atom Publishing Protocol. As such, implementers must understand the security considerations described in those specifications.
In addition, there are a number of additional security considerations that are unique to this specification.
The approach described herein is based upon all policy enforcements being implemented at the point when a resource representation is created. As such, producers sharing cyber security information using this specification must take care to authenticate their HTTP clients using a suitably strong user authentication mechanism. Sharing communities that are exchanging information on well-known indicators and incidents for purposes of public education may choose to rely upon, e.g. HTTP Authentication, or similar. However, sharing communities that are engaged in sensitive collaborative analysis and/or operational response for indicators and incidents targeting high value information systems should adopt a suitably stronger user authentication solution, such as TLS client certificates, or a risk-based or multi-factor approach. In general, trust in the sharing consortium will depend upon the members maintaining adequate user authentication mechanisms.
Collaborating consortiums may benefit from the adoption of a federated identity solution, such as those based upon SAML-core [SAML-core] and SAML-bind [SAML-bind] and SAML-prof [SAML-prof] for Web-based authentication and cross-organizational single sign-on. Dependency on a trusted third party identity provider implies that appropriate care must be exercised to sufficiently secure the Identity provider. Any attacks on the federated identity system would present a risk to the CSIRT, as a relying party. Potential mitigations include deployment of a federation-aware identity provider that is under the control of the information sharing consortium, with suitably stringent technical and management controls.
All security measures MUST be enforced at the source, that is, a provider SHALL NOT return any feed content or member entry content for which the client identity has not been specifically authenticated, authorized, and audited.
Sharing communities that have a requirement for forward message security (such that client systems are required to participate in providing message level security and/or distributed authorization policy enforcement), MUST use TODO.
The implementation details of the authorization scheme chosen by a ROLIE-compliant provider are out of scope for this specification. Implementers are free to choose any suitable authorization mechanism that is capable of fulfilling the policy enforcement requirements relevant to their consortium and/or organization.
Authorization of resource representations is the responsibility of the source system, i.e. based on the authenticated user identity associated with an HTTP(S) request. The required authorization policies that are to be enforced must therefore be managed by the security administrators of the source system. Various authorization architectures would be suitable for this purpose, such as RBAC and/or ABAC, as embodied in XACML [XACML]. In particular, implementers adopting XACML may benefit from the capability to represent their authorization policies in a standardized, interoperable format.
Additional security requirements such as enforcing message-level security at the destination system could supplement the security enforcements performed at the source system, however these destination-provided policy enforcements are out of scope for this specification. Implementers requiring this capability should consider leveraging, e.g. the <RIDPolicy> element in the RID schema. Refer to RFC6545 section 9 for more information.
When security policies relevant to the source system are to be enforced at both the source and destination systems, implementers must take care to avoid unintended interactions of the separately enforced policies. Potential risks will include unintended denial of service and/or unintended information leakage. These problems may be mitigated by avoiding any dependence upon enforcements performed at the destination system. When distributed enforcement is unavoidable, the usage of a standard language (e.g. XACML) for the expression of authorization policies will enable the source and destination systems to better coordinate and align their respective policy expressions.
Adoption of the information sharing approach described in this document will enable users to more easily perform correlations across separate, and potentially unrelated, cyber security information providers. A client may succeed in assembling a data set that would not have been permitted within the context of the authorization policies of either provider when considered individually. Thus, providers may face a risk of an attacker obtaining an access that constitutes an undetected separation of duties (SOD) violation. It is important to note that this risk is not unique to this specification, and a similar potential for abuse exists with any other cyber security information sharing protocol. However, the wide availability of tools for HTTP clients and Atom feed handling implies that the resources and technical skills required for a successful exploit may be less than it was previously. This risk can be best mitigated through appropriate vetting of the client at account provisioning time. In addition, any increase in the risk of this type of abuse should be offset by the corresponding increase in effectiveness that this specification affords to the defenders.
While it is a goal of this specification to enable more agile cyber security information sharing across a broader and varying constituency, there is nothing in this specification that necessarily requires this type of deployment. A cyber security information sharing consortium may chose to adopt this specification while continuing to operate as a gated community with strictly limited membership.
The author gratefully acknowledges the valuable contributions of Tom Maguire, Kathleen Moriarty, and Vijayanand Bharadwaj. These individuals provided detailed review comments on earlier drafts, and many suggestions that have helped to improve this document .
| [RFC2141] | Moats, R., "URN Syntax", RFC 2141, DOI 10.17487/RFC2141, May 1997. |
| [RFC3444] | Pras, A. and J. Schoenwaelder, "On the Difference between Information Models and Data Models", RFC 3444, DOI 10.17487/RFC3444, January 2003. |
| [RFC6545] | Moriarty, K., "Real-time Inter-network Defense (RID)", RFC 6545, DOI 10.17487/RFC6545, April 2012. |
| [I-D.ietf-mile-rfc5070-bis] | Danyliw, R., "The Incident Object Description Exchange Format v2", Internet-Draft draft-ietf-mile-rfc5070-bis-25, June 2016. |
| [XACML] | Rissanen, E., "eXtensible Access Control Markup Language (XACML) Version 3.0", August 2010. |
| [REST] | Fielding, R., "Architectural Styles and the Design of Network-based Software Architectures", 2000. |
This section provides a non-normative example of a client doing service discovery. TODO: Standardize location of doc?
An Atom service document enables a client to dynamically discover what feeds a particular publisher makes available. Thus, a provider uses an Atom service document to enable clients or other authorized parties to determine what specific information the provider makes available to the community. The service document could be made available at any well known location, such as via a link from the CSIRT's home page. One common technique is to include a link in the <HEAD> section of the organization's home page, as shown below:
Example of bootstrapping Service Document discovery:
<link rel="introspection"
type="application/atomsvc+xml"
title="Atom Publishing Protocol Service Document"
href="/csirt/svcdoc.xml" />
A client may then format an HTTP GET request to retrieve the service document:
GET /provider/svcdoc.xml Host: www.example.org Accept: application/atomsvc+xml
Notice the use of the HTTP Accept: request header, indicating the MIME type for Atom service discovery. The response to this GET request will be an XML document that contains information on the specific feed collections that are provided by the CSIRT.
Example HTTP GET response:
HTTP/1.1 200 OK
Date: Fri, 24 Aug 2012 17:09:11 GMT
Content-Length: 570
Content-Type: application/atomsvc+xml;charset="utf-8"
<?xml version="1.0" encoding="UTF-8"?>
<service xmlns="http://www.w3.org/2007/app"
xmlns:atom="http://www.w3.org/2005/Atom"
xmlns:xml="http://www.w3.org/XML/1998/namespace"
xml:lang="en-US">
<workspace>
<atom:title type="text">Incidents</atom:title>
<collection href="http://example.org/provider/incidents">
<atom:title type="text">Incidents Feed</atom:title>
<categories fixed="yes">
<atom:category
scheme="urn:ietf:params:rolie:information-type"
term="vulnerability"/>
</categories>
<accept>application/atom+xml; type=entry</accept>
</collection>
</workspace>
</service>
This simple Service Document example shows that this server provides one workspace, named "Incidents". Within that workspace, the producer makes one feed collection available. When attempting to GET or POST entries to that feed collection, the client must indicate a content type of application/atom+xml.
A server may also offer a number of different feeds, each containing different types of security automation information. In the following example, the feeds have been categorized. This categorization will help the clients to decide which feeds will meet their needs.
HTTP/1.1 200 OK
Date: Fri, 24 Aug 2012 17:10:11 GMT
Content-Length: 1912
Content-Type: application/atomsvc+xml;charset="utf-8"
<?xml version="1.0" encoding='utf-8'?>
<service xmlns="http://www.w3.org/2007/app"
xmlns:atom="http://www.w3.org/2005/Atom">
<workspace>
<atom:title>Public Security Information Sharing</atom:title>
<collection
href="http://example.org/provider/public/vulnerabilties">
<atom:title>Public Vulnerabilities</atom:title>
<accept>application/atom+xml; type=entry</accept>
<categories fixed="yes">
<atom:category
scheme="urn:ietf:params:rolie:information-type"
term="vulnerability"/>
</categories>
</collection>
<collection
href="http://example.org/provider/public/incidents">
<atom:title>Public Incidents</atom:title>
<accept>application/atom+xml; type=entry</accept>
<categories fixed="yes">
<atom:category
scheme="urn:ietf:params:rolie:information-type"
term="incident"/>
</categories>
</collection>
</workspace>
<workspace>
<atom:title>Private Consortium Sharing</atom:title>
<collection
href="http://example.org/provider/private/incidents" >
<atom:title>Incidents</atom:title>
<accept>application/atom+xml;type=entry</accept>
<categories fixed="yes">
<atom:category
scheme="urn:ietf:params:rolie:information-type"
term="incident"/>
</categories>
</collection>
</workspace>
</service>
In this example, the CSIRT is providing a total of three feed collections, organized into two different workspaces. The first workspace contains two feeds, consisting of publicly available software vulnerabilities and publicly available incidents, respectively. The second workspace provides one additional feed, for use by a sharing consortium. The feed contains incident information containing entries related to three purposes: traceback, mitigation, and reporting. The entries in this feed are categorized with a restriction of either "Need-to-Know" or "private". An appropriately authenticated and authorized client may then proceed to make GET requests for one or more of these feeds. The publicly provided incident information may be accessible with or without authentication. However, users accessing the feed targeted to the private sharing consortium would be expected to authenticate, and appropriate authorization policies would subsequently be enforced by the feed provider.
This section provides a non-normative example of a client retrieving an incident feed. TODO
Having discovered the available security information sharing feeds, an authenticated and authorized client who is a member of the private sharing consortium may be interested in receiving the feed of known incidents. The client may retrieve this feed by performing an HTTP GET operation on the indicated URL.
Example HTTP GET request for a Feed:
GET /provider/private/incidents Host: www.example.org Accept: application/atom+xml
The corresponding HTTP response would be an XML document containing the incidents feed:
Example HTTP GET response for a Feed:
HTTP/1.1 200 OK
Date: Fri, 24 Aug 2012 17:20:11 GMT
Content-Length: 2882
Content-Type: application/atom+xml;type=feed;charset="utf-8"
<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom"
xml:lang="en-US">
<generator version="1.0">
Example Provider ROLIE Feed Generator
</generator>
<id>http://www.example.org/provider/private/incidents</id>
<title type="text">
Atom formatted representation of
a feed of XML incident documents
</title>
<!-- The category is taken from the related IANA table -->
<atom:category
scheme="urn:ietf:params:rolie:information-type"
term="incident"/>
<updated>2012-05-04T18:13:51.0Z</updated>
<author>
<email>provider@example.org</email>
<name>Example Provider</name>
</author>
<!-- By convention there is usually a self link for the feed -->
<link href="http://www.example.org/provider/private/incidents"
rel="self" type="application/atom+xml"/>
<entry>
<id>
http://www.example.org/provider/private/incidents/123456
</id>
<title>Sample Incident</title>
<!-- by convention -->
<link
href="http://www.example.org/provider/private/incidents/12345"
rel="self" type="application/atom+xml"/>
<!-- required by Atom spec -->
<link
href="http://www.example.org/provider/private/incidents/12345"
rel="alternate" type="xml"/>
<published>2014-08-04T18:13:51.0Z</published>
<updated>2014-08-05T18:13:51.0Z</updated>
<summary>A short description of this resource</summary>
</entry>
<entry>
<!-- ...another entry... -->
</entry>
</feed>
This feed document has two atom entries, one of which has been elided. The completed entry illustrates an Atom <entry> element that provides a summary of essential details about one particular incident. Based upon this summary information and the provided category information, a client may choose to do an HTTP GET operation to retrieve the full details of the incident. This example exemplifies the benefits a RESTful alternative has to traditional point-to-point messaging systems.
This section provides a non-normative example of a client retrieving an incident as an Atom entry. TODO
Having retrieved the feed of interest, the client may then decide based on the description and/or category information that one of the entries in the feed is of further interest. The client may retrieve this incident Entry by performing an HTTP GET operation on the indicated URL.
Example HTTP GET request for an Entry:
GET /provider/private/incidents/123456 Host: www.example.org Accept: application/atom+xml
The corresponding HTTP response would be an XML document containing the incident:
Example HTTP GET response for an Entry:
HTTP/1.1 200 OK
Date: Fri, 24 Aug 2012 17:30:11 GMT
Content-Length: 4965
Content-Type: application/atom+xml;type=entry;charset="utf-8"
<?xml version="1.0" encoding="UTF-8"?>
<entry>
<id>http://www.example.org/provider/private/incidents/123456</id>
<title>Sample Incident</title>
<!-- by convention -->
<link href="http://www.example.org/csirt/private/incidents/123456"
rel="self" type="application/atom+xml"/>
<!-- required by Atom spec -->
<link href="http://www.example.org/csirt/private/incidents/123456"
rel="alternate" type="IODEF"/>
<published>2012-08-04T18:13:51.0Z</published>
<updated>2012-08-05T18:13:51.0Z</updated>
<!-- The category is taken from the related IANA table -->
<atom:category
scheme="urn:ietf:params:rolie:information-type"
term="incident"/>
<summary>A short description of this incident resource</summary>
<!-- Typical operations that can be
performed on this entry include edit -->
<link href="http://www.example.org/csirt/private/incidents/123456"
rel="edit"/>
<!-- the next and previous are just sequential access,
may not map to anything related to this resource -->
<link href="http://www.example.org/csirt/private/incidents/123457"
rel="next"/>
<link href="http://www.example.org/csirt/private/incidents/123455"
rel="previous"/>
<!-- navigate up to the full collection.
Might also be rel="collection" as per IANA registry -->
<link href="http://www.example.org/csirt/private/incidents"
rel="up"/>
<content type="application/xml">
<xml>
<tag>
<data> Example </data>
</tag>
</xml>
</content>
</entry>
As can be seen in the example response, above, an XML document is contained within the Atom <content> element. The client may now process the XML document as needed.
Note also that, as described previously, the content of the Atom <category> element is application-defined. The Atom categories have been assigned based on the IANA table content model.
Finally, it should be noted that in order to optimize the client experience, and avoid an additional round trip, a feed provider may choose to include the entry content inline, as part of the feed document. That is, an Atom <entry> element within a Feed document may contain an Atom <content> element as a child. In this case, the client will receive the full content of the entries within the feed. The decision of whether to include the entry content inline or to include it as a link is a design choice left to the feed provider (e.g. based upon local environmental factors such as the number of entries contained in a feed, the available network bandwidth, the available server compute cycles, the expected client usage patterns, etc.).
This section provides a non-normative example of a search use case.
The following example provides a RESTful solution to handling search results. Note that in the RESTful approach described herein there is no requirement to define a query language. Instead, implementations may provide support for search operations via existing search facilities, and advertise these capabilities via an appropriate URL template. Clients dynamically retrieve the search description document, and invoke specific searches via an instantiated URL template.
An HTTP response body may include a link relationship of type "search." This link provides a reference to an OpenSearch description document.
Example HTTP response that includes a "search" link:
HTTP/1.1 200 OK
Date: Fri, 24 Aug 2012 17:20:11 GMT
Content-Length: nnnn
Content-Type: application/atom+xml;type=feed;charset="utf-8"
<?xml version="1.0" encoding="UTF-8"?>
<feed xmlns="http://www.w3.org/2005/Atom"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.w3.org/2005/Atom file:/
C:/schemas/atom.xsd
urn:ietf:params:xml:ns:iodef-1.0
file:/C:/schemas/iodef-1.0.xsd"
xml:lang="en-US">
<link href="http://www.example.org/opensearchdescription.xml"
rel="search"
type="application/opensearchdescription+xml"
title="CSIRT search facility" />
<!-- ...other links... -->
<entry>
<!-- ...zero or more entries... -->
</entry>
</feed>
The OpenSearch Description document contains the information needed by a client to request a search. An example of an Open Search description document is shown below:
Example HTTP response that includes a "search" link:
<?xml version="1.0" encoding="UTF-8"?>
<OpenSearchDescription xmlns="http://a9.com/-/spec/opensearch/1.1/">
<ShortName>CSIRT search example</ShortName>
<Description>Cyber security information
sharing consortium search interface</Description>
<Tags>example csirt indicator search</Tags>
<Contact>admin@example.org</Contact>
<!-- optionally, other elements, as per OpenSearch specification -->
<Url type="application/opensearchdescription+xml" rel="self"
template="http://www.example.com/csirt/opensearchdescription.xml"/>
<Url type="application/atom+xml" rel="results"
template="http://www.example.org/csirt?q={searchTerms}&
format=Atom+xml"/>
<LongName>www.example.org CSIRT search</LongName>
<Query role="example" searchTerms="incident" />
<Language>en-us</Language>
<OutputEncoding>UTF-8</OutputEncoding>
<InputEncoding>UTF-8</InputEncoding>
</OpenSearchDescription>
The OpenSearch Description document shown above contains two <Url> elements that contain parametrized URL templates. These templates provide a representation of how the client should make search requests. The exact format of the query string, including the parametrization is specified by the feed provider
This OpenSearch Description Document also contains an example of a <Query> element. Each <Query> element describes a specific search request that can be made by the client. Note that the parameters of the <Query> element correspond to the URL template parameters. In this way, a provider may fully describe the search interface available to the clients. The search section, above, provides specific NORMATIVE requirements for the use of Open Search.
ROLIE assumes that all authorization policy enforcement is provided at the source server. The implementation details of the authorization scheme chosen by a ROLIE-compliant provider are out of scope for this specification. Implementers are free to choose any suitable authorization mechanism that is capable of fulfilling the policy enforcement requirements relevant to their consortium and/or organization.
It is well known that one of the major barriers to information sharing is ensuring acceptable use of the information shared. In the case of ROLIE, one way to lower that barrier may be to develop a XACML profile. Use of XACML would allow a ROLIE-compliant provider to express their information sharing authorization policies in a standards-compliant, and machine-readable format.
This improved interoperability may, in turn, enable more agile interactions in the cyber security sharing community. For example, a peer CSIRT, or another interested stakeholder such as an auditor, would be able to review and compare CSIRT sharing policies using appropriate tooling.
The XACML 3.0 standard is based upon the notion that authorization policies are defined in terms of predicate logic expressions written against the attributes associated with one or more of the following four entities:
Thus, a suitable approach to a XACML 3.0 profile for ROLIE authorization policies could begin by using the 3-tuple of [SUBJECT, ACTION, RESOURCE] where:
Implementers who have a need may also choose to evaluate based upon the additional ENVIRONMENT factors, such as current threat level, and so on. One could also write policy to consider the CVSS score associated with the resource, or the lifecycle phase of the resource (vulnerability unverified, confirmed, patch available, etc.), and so on.
Having these policies expressed in a standards-compliant and machine-readable format could improve the agility and effectiveness of a cyber security information sharing group or consortium, and enable better cyber defenses.
TODO
Changes since draft-field-mile-rolie-01 version, December, 2015 to May 27, 2016:
Changes made in draft-ietf-mile-rolie-01 since draft-field-mile-rolie-02 version, August 15, 2013 to December 2, 2015: