CVE-2021-29471

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.

How to fix CVE-2021-29471

To remediate CVE-2021-29471, upgrade the affected package to a fixed version below.

• —upgrade to 1.33.2-1 or later
• —upgrade to 1.33.2 or later
• —upgrade to 03318a766cac9f8b053db2214d9c332a977d226c or later

Is CVE-2021-29471 being exploited?

Low — EPSS is 0.3%, meaning exploitation activity has not been observed at scale.

Affected packages (3)

• from 0, < 1.33.2-1
• from 0, < 1.33.2
• from 0, < 03318a766cac9f8b053db2214d9c332a977d226c | from 0, < 1.33.2

CVSS scores

References (8)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2021-29471
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2021-29471
• PATCHgithub.com/matrix-org/synapse
• WEBgithub.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226c