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CVE-2021-29471

Published: 11 May 2021

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.

Priority

Medium

Cvss 3 Severity Score

5.3

Score breakdown

Status

Package Release Status
matrix-synapse
Launchpad, Ubuntu, Debian
bionic Needed

focal Needed

groovy Ignored
(end of life)
hirsute Ignored
(end of life)
impish Ignored
(end of life)
jammy Needed

kinetic Ignored
(end of life, was needed)
lunar Not vulnerable
(1.64.0-3)
mantic Not vulnerable
(1.64.0-3)
noble Not vulnerable
(1.64.0-3)
trusty Does not exist

upstream
Released (1.33.2-1)
xenial Ignored
(end of standard support)
Patches:
upstream: https://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226c

Severity score breakdown

Parameter Value
Base score 5.3
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Scope Unchanged
Confidentiality None
Integrity impact None
Availability impact Low
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L