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Denial of service attack via push rule patterns in matrix-synapse

Low severity GitHub Reviewed Published May 11, 2021 in matrix-org/synapse • Updated Feb 1, 2023

Package

pip matrix-synapse (pip)

Affected versions

< 1.33.2

Patched versions

1.33.2

Description

Impact

"Push rules" can specify conditions under which they will match, including event_match, which matches event content against a pattern including wildcards.

Certain patterns can cause very poor performance in the matching engine, leading to a denial-of-service when processing moderate length events.

Patches

The issue is patched by matrix-org/synapse@03318a7.

Workarounds

A potential workaround might be to prevent users from making custom push rules, by blocking such requests at a reverse-proxy.

For more information

If you have any questions or comments about this advisory, email us at [email protected].

References

@richvdh richvdh published to matrix-org/synapse May 11, 2021
Published by the National Vulnerability Database May 11, 2021
Reviewed May 11, 2021
Published to the GitHub Advisory Database May 13, 2021
Last updated Feb 1, 2023

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS score

0.154%
(52nd percentile)

Weaknesses

CVE ID

CVE-2021-29471

GHSA ID

GHSA-x345-32rc-8h85

Source code

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