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CVE-2021-29471

LOW
Published 2021-05-11T15:05:12
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Expert Analysis

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CVSS Score

V3.1
3.7
/10
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Base Score Metrics
Exploitability: N/A Impact: N/A

EPSS Score

v2025.03.14
0.006
probability
of exploitation in the wild

There is a 0.6% chance that this vulnerability will be exploited in the wild within the next 30 days.

Updated: 2025-06-25
Exploit Probability
Percentile: 0.688
Higher than 68.8% of all CVEs

Attack Vector Metrics

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED

Impact Metrics

Confidentiality
NONE
Integrity
NONE
Availability
LOW

Description

Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.33.2 "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. The issue is patched in version 1.33.2. A potential workaround might be to prevent users from making custom push rules, by blocking such requests at a reverse-proxy.

Available Exploits

No exploits available for this CVE.

Related News

No news articles found for this CVE.

Affected Products

matrix-org

synapse

Affected Versions:

< 1.33.2

GitHub Security Advisories

Community-driven vulnerability intelligence from GitHub

✓ GitHub Reviewed MODERATE

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

GHSA-x345-32rc-8h85

Advisory Details

### Impact "Push rules" can specify [conditions](https://matrix.org/docs/spec/client_server/r0.6.1#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 https://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226c. ### 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].

Affected Packages

PyPI matrix-synapse
ECOSYSTEM: ≥0 <1.33.2

CVSS Scoring

CVSS Score

5.0

CVSS Vector

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

References

WEB https://github.com/matrix-org/synapse/security/advisories/GHSA-x345-32rc-8h85
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2021-29471
WEB https://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226c
PACKAGE https://github.com/matrix-org/synapse
WEB https://github.com/matrix-org/synapse/releases/tag/v1.33.2
WEB https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-135.yaml
WEB https://lists.fedoraproject.org/archives/list/[email protected]/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY

Advisory provided by GitHub Security Advisory Database. Published: May 13, 2021, Modified: September 30, 2024

References

https://github.com/matrix-org/synapse/security/advisories/GHSA-x345-32rc-8h85
https://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226c
https://github.com/matrix-org/synapse/releases/tag/v1.33.2
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/
Published: 2021-05-11T15:05:12
Last Modified: 2024-08-03T22:11:05.476Z
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