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

Cvss 3 Severity Score

5.3

Score breakdown

Status

Package	Release	Status
matrix-synapse Launchpad, Ubuntu, Debian	hirsute	Ignored (end of life)
	upstream	Released (1.33.2-1)
	jammy	Needed
	bionic	Needed
	focal	Needed
	trusty	Does not exist
	xenial	Ignored (end of standard support)
	groovy	Ignored (end of life)
	impish	Ignored (end of life)
	kinetic	Ignored (end of life, was needed)
	lunar	Not vulnerable (1.64.0-3)
	mantic	Not vulnerable (1.64.0-3)
	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

References

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