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Vulnerability · Published May 11, 2021 · Assigned by GitHub_M

CVE-2021-29471Denial of service in Matrix Synapse

Low 3.7

In plain English

A low-severity uncontrolled resource consumption in synapse from matrix-org. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 1.6% (higher than 77% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)3.7Low
Exploit odds (30 days)1.6%top 23.4% of all CVEs
Exploited in the wildNo reportsnot in CISA KEV
Attack toolingNoneno public tooling known

Official 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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Alpine:v3.20synapse1.33.2-r0ALPINE-CVE-2021-29471
Alpine:v3.21synapse1.33.2-r0ALPINE-CVE-2021-29471
Alpine:v3.22synapse1.33.2-r0ALPINE-CVE-2021-29471
Alpine:v3.23synapse1.33.2-r0ALPINE-CVE-2021-29471
Alpine:v3.24synapse1.33.2-r0ALPINE-CVE-2021-29471
Debian:14matrix-synapse1.33.2-1DEBIAN-CVE-2021-29471
PyPImatrix-synapse1.33.2GHSA-x345-32rc-8h85
PyPImatrix-synapse1.33.2PYSEC-2021-135

Affected products (as reported)

VendorProductVersions
matrix-org synapse < 1.33.2

Weakness: CWE-400 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

References