Arch Linux alert ASA-202105-19 (matrix-synapse)

From:
             
 
Jonas Witschel via arch-security <arch-security@lists.archlinux.org>
To:
             
 
arch-security@lists.archlinux.org
Subject:
             
 
[ASA-202105-19] matrix-synapse: denial of service
Date:
             
 
Wed, 26 May 2021 12:32:44 +0200
Message-ID:
             
 
<20210526103244.epihjlvyc4kq2jgo@archlinux.org>
Cc:
             
 
Jonas Witschel <diabonas@archlinux.org>
Arch Linux Security Advisory ASA-202105-19
==========================================

Severity: Medium
Date    : 2021-05-25
CVE-ID  : CVE-2021-29471
Package : matrix-synapse
Type    : denial of service
Remote  : Yes
Link    : https://security.archlinux.org/AVG-1943

Summary
=======

The package matrix-synapse before version 1.33.2-1 is vulnerable to
denial of service.

Resolution
==========

Upgrade to 1.33.2-1.

# pacman -Syu "matrix-synapse>=1.33.2-1"

The problem has been fixed upstream in version 1.33.2.

Workaround
==========

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

Description
===========

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.

Impact
======

A remote attacker could cause high CPU usage on the server using
crafted push rules, leading to denial of service.

References
==========

https://bugs.archlinux.org/task/70801
https://github.com/matrix-org/synapse/security/advisories...
https://github.com/matrix-org/synapse/commit/03318a766cac...
https://security.archlinux.org/CVE-2021-29471