CVE-2021-29471

medium

Published 2021-05-13 · Modified 2023-11-08

💬 Discuss on Community ✚ Propose mitigation

CVSS v3

—

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

CVSS v4 NEW

—

not yet in upstream

VIR risk

5.5

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.

Predictions

Exploit likelihood

30%

Patch ETA

—

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

No mitigations published for this CVE yet.

The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.

✚ Propose a mitigation on Community → Mitigations published via the community go through AI scoring + 2 human reviewers + 7-day silent objection window before landing here with source_tier=community-verified.

OS impact

Arch Fixed 1 release

Version	Status	Fixed in
—	Fixed	`1.33.2-1`

Debian Fixed 2 releases

Version	Status	Fixed in
sid	Fixed	`1.33.2-1`
forky	Fixed	`1.33.2-1`

Package impact

Ecosystem	Package	Vulnerable	Fixed
PyPI	matrix-synapse	`<1.33.2`	`1.33.2`
PyPI	matrix-synapse	`<03318a766cac9f8b053db2214d9c332a977d226c\|\|<1.33.2`	`03318a766cac9f8b053db2214d9c332a977d226c`

References

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.