Unfortunately, not all XMPP entities are well-behaved. Currently, if an XMPP entity (the "attacker") sends abusive stanzas to another XMPP entity (the "victim"), there is no way for the victim or the victim's server to inform the attacker's server that the attacker is generating abusive traffic. In practice, the victim's server may need to terminate the server-to-server connection (currently without explicitly informing the attacker's server about the reason for the termination) rather than continue to accept the abusive traffic.
This situation is far from desirable. Therefore, this specification defines three small XMPP protocol functions that can help to improve the reliability of server-to-server connections:
An abuse report MUST be sent in an IQ stanza of type "set" containing an <abuse/> element qualified by the 'urn:xmpp:tmp:abuse' namespace (see Protocol Namespaces regarding issuance of one or more permanent namespaces). The allowable children of the <abuse/> element are:
This specification intentionally does not define exactly what constitutes abuse, since "abuse is in the eye of the beholder". However, the following machine-readable conditions are defined as children of the <reason/> element.
| Condition | Definition |
|---|---|
| <gateway/> | Attempting to inappropriately use a gateway on the receiving server (see Gateway Interaction (XEP-0100) [1]) |
| <muc/> | Attempting to take over or otherwise abuse Multi-User Chat (XEP-0045) [2] rooms on the receiving server |
| <proxy/> | Attempting to inappropriately use a SOCKS5 Bytestreams (XEP-0065) [3] proxy, TURN server, or other proxy on the receiving server |
| <pubsub/> | Attempting to inappropriately use a Publish-Subscribe (XEP-0060) [4] service on the receiving server |
| <service/> | Attempting to inappropriately use any other kind of service on the receiving server |
| <spam/> | Sending spam (unsolicited bulk messages) |
| <stanza-too-big/> | Sending extremely large stanzas |
| <too-many-recipients/> | Sending messages that contain too many recipients (see Extended Stanza Addressing (XEP-0033) [5]) |
| <too-many-stanzas/> | Sending an extremely large number of stanzas |
| <unacceptable-payload/> | Sending messages that contain unacceptable payloads such as malicious executables |
| <unacceptable-text/> | Sending messages that contain unacceptable human-readable text |
| <undefined-abuse/> | The abuse condition is undefined (should be used with an application-specific condition) |
Note: The foregoing list of conditions is not exhaustive. The list may be augmented or otherwise modified in a future version of this specification as a result of implementation and deployment experience.
If an XMPP server receives abusive stanzas over a server-to-server connection, the receiving server SHOULD send an abuse report to the sending server.
<iq from='example.org'
id='rep1'
to='example.com'
type='set'>
<abuse xmlns='urn:xmpp:tmp:abuse'>
<jid>abuser@example.com/foo</jid>
<reason>
<condition>
<muc/>
</condition>
</reason>
</abuse>
</iq>
Upon receiving the abuse report, the sending server MUST proceed as follows.
If the sending server does not understand the abuse reporting protocol, it MUST return a <service-unavailable/> error to the receiving server.
<iq from='example.com'
id='rep1'
to='example.org'
type='error'>
<error type='cancel'>
<service-unavailable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
If none of the JIDs contained in the abuse report exist at the sending server, the sending server MUST return an <item-not-found/> error to the receiving server.
<iq from='example.com'
id='rep1'
to='example.org'
type='error'>
<error type='cancel'>
<item-not-found xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
</iq>
If the sending server accepts the abuse report for one or more JIDs, it MUST return an IQ stanza of type "result" to the receiving server.
<iq from='example.com'
id='rep1'
to='example.org'
type='result'/>
This specification does not define how a sending server shall behave when it receives an abuse report. In general it is expected that the sending server (1) will notify the human administrators of the server in some implementation-specific or deployment-specific fashion, and (2) may use the abuse report in an automated fashion (e.g., as input to a rate-limiting algorithm, reputation system, or decision about temporarily suspending the privileges of the sending entity or entities). In addition, the sending server MAY the report to trusted parties such as third-party reporting services.
The receiving server MAY report that a particular stanza is considered abusive. The stanza error condition MUST be <not-acceptable/> and the error stanza MUST include an application-specific error condition of <abuse/> qualified by the 'urn:xmpp:tmp:abuse' (see Protocol Namespaces regarding issuance of one or more permanent namespaces). The <abuse/> element MUST include one or more <jid/> elements whose XML character data specifies the JID(s) of the abusive sender(s).
<message from='abuser@example.org/foo'
to='victim@example.org'>
[ ... some abusive payload here ... ]
</message>
<message from='example.com'
to='example.org'>
<error type='cancel'>
<not-acceptable xmlns='urn:ietf:params:xml:ns:xmpp-stanzas'/>
</error>
<abuse xmlns='urn:xmpp:tmp:abuse'>
<jid>abuser@example.com/foo</jid>
<reason>
<condition>
<unacceptable-payload/>
</condition>
</reason>
</abuse>
</message>
If the sending entity continues to generate abusive stanzas via the sending server, the receiving server MAY close the stream between the receiving server and the sending server. The stream error condition MUST be <policy-violation/> and the stream error MUST include an application-specific error condition of <abuse/> qualified by the 'urn:xmpp:tmp:abuse'. The <abuse/> element MUST include one or more <jid/> elements whose XML character data specifies the JID(s) of the abusive sender(s).
<stream:error>
<policy-violation xmlns='urn:ietf:params:xml:ns:xmpp-streams'/>
<abuse xmlns='urn:xmpp:tmp:abuse'>
<jid>abuser@example.com/foo</jid>
<reason>
<condition>
<too-many-stanzas/>
</condition>
</reason>
</abuse>
</stream:error>
</stream:stream>
The receiving entity then SHOULD terminate the TCP connection between the receiving server and the sending server.
If a server supports the abuse reporting protocol, it MUST report that fact by including a service discovery feature of "urn:xmpp:tmp:abuse" (see Protocol Namespaces regarding issuance of one or more permanent namespaces) in response to a Service Discovery (XEP-0030) [6] information request:
<iq from='example.org'
id='disco1'
to='example.com'
type='get'>
<query xmlns='http://jabber.org/protocol/disco#info'/>
</iq>
<iq from='example.com'
id='disco1'
to='example.org'
type='result'>
<query xmlns='http://jabber.org/protocol/disco#info'>
...
<feature var='urn:xmpp:tmp:abuse'/>
...
</query>
</iq>
It is possible for an abusive sender to launch a denial of service attack against legitimate users of the sending server by generating abusive traffic over the server-to-server connection (in fact such attacks have already been observed on XMPP networks). Although use of the abuse reporting protocol does not completely prevent such attacks, it may at least enable sending servers to react to abusive traffic in close to real time, thus helping to "heal" the network when denial of service attacks are launched.
If a malicious entity can inject information into the server-to-server connection, it can falsely send abuse reports to the sending server. Therefore the connection SHOULD be encrypted using Transport Layer Security as specified in XMPP Core [7].
This document requires no interaction with the Internet Assigned Numbers Authority (IANA) [8].
Until this specification advances to a status of Draft, its associated namespace shall be "urn:xmpp:tmp:abuse"; upon advancement of this specification, the XMPP Registrar [9] shall issue a permanent namespace in accordance with the process defined in Section 4 of XMPP Registrar Function (XEP-0053) [10].
The XMPP Registrar shall add <abuse/> to its registry of application-specific error conditions (see <https://xmpp.org/registrar/errors.html>), where the element is qualified by the 'urn:xmpp:tmp:abuse' namespace (see Protocol Namespaces regarding issuance of one or more permanent namespaces).
The registry submission is as follows:
<condition> <ns>urn:xmpp:tmp:abuse</ns> <element>abuse</element> <desc>the sending entity has generated traffic that the receiving server considers abusive</desc> <doc>XEP-xxxx</doc> </condition>
<?xml version='1.0' encoding='UTF-8'?>
<xs:schema
xmlns:xs='http://www.w3.org/2001/XMLSchema'
targetNamespace='urn:xmpp:tmp:abuse'
xmlns='urn:xmpp:tmp:abuse'
elementFormDefault='qualified'>
<xs:element name='abuse'>
<xs:complexType>
<xs:sequence>
<xs:element name='jid' type='xs:string' minOccurs='1' maxOccurs='unbounded'/>
<xs:element ref='reason' minOccurs='0'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='reason'>
<xs:complexType>
<xs:sequence>
<xs:element ref='condition' minOccurs='0' maxOccurs='1'/>
<xs:element name='text' type='xs:string' minOccurs='0' maxOccurs='1'/>
<xs:any namespace='##other' minOccurs='0' maxOccurs='1'/>
</xs:sequence>
</xs:complexType>
</xs:element>
<xs:element name='condition'>
<xs:complexType>
<xs:choice>
<xs:element name='gateway' type='empty'/>
<xs:element name='muc' type='empty'/>
<xs:element name='proxy' type='empty'/>
<xs:element name='pubsub' type='empty'/>
<xs:element name='service' type='empty'/>
<xs:element name='spam' type='empty'/>
<xs:element name='stanza-too-big' type='empty'/>
<xs:element name='too-many-recipients' type='empty'/>
<xs:element name='too-many-stanzas' type='empty'/>
<xs:element name='unacceptable-payload' type='empty'/>
<xs:element name='unacceptable-text' type='empty'/>
<xs:element name='undefined-abuse' type='empty'/>
</xs:choice>
</xs:complexType>
</xs:element>
<xs:simpleType name='empty'>
<xs:restriction base='xs:string'>
<xs:enumeration value=''/>
</xs:restriction>
</xs:simpleType>
</xs:schema>
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Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.
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This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.
Discussion on other xmpp.org discussion lists might also be appropriate; see <http://xmpp.org/about/discuss.shtml> for a complete list.
Errata can be sent to <editor@xmpp.org>.
The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
1. XEP-0100: Gateway Interaction <https://xmpp.org/extensions/xep-0100.html>.
2. XEP-0045: Multi-User Chat <https://xmpp.org/extensions/xep-0045.html>.
3. XEP-0065: SOCKS5 Bytestreams <https://xmpp.org/extensions/xep-0065.html>.
4. XEP-0060: Publish-Subscribe <https://xmpp.org/extensions/xep-0060.html>.
5. XEP-0033: Extended Stanza Addressing <https://xmpp.org/extensions/xep-0033.html>.
6. XEP-0030: Service Discovery <https://xmpp.org/extensions/xep-0030.html>.
7. RFC 6120: Extensible Messaging and Presence Protocol (XMPP): Core <http://tools.ietf.org/html/rfc6120>.
8. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
9. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.
10. XEP-0053: XMPP Registrar Function <https://xmpp.org/extensions/xep-0053.html>.
Note: Older versions of this specification might be available at http://xmpp.org/extensions/attic/
Retracted in favor of XEP-0161, which now contains the content originally published in this specification.
Initial published version.
Added reason element containing machine-readable conditions and optional human-readable text; added note about forwarding of abuse reports.
Limited scope to reporting between two servers; more clearly defined what is abusive; changed protocol to use IQ request-response exchange; limited use of error condition to stream termination.
First draft.
END