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CVE-2021-29471

3.7 · LOW

Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse).

Published May 11, 2021CWE-400EPSS 1.65%

Overview

CVE-2021-29471 is a low-severity vulnerability. It was published on May 11, 2021 and has a CVSS 3.1 base score of 3.7 (LOW).

This vulnerability has a CVSS 3.1 base score of 3.7, rated LOW. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

References

GitHubgithub.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226cGitHubgithub.com/matrix-org/synapse/releases/tag/v1.33.2GitHubgithub.com/matrix-org/synapse/security/advisories/GHSA-x345-32rc-8h85Reflists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/GitHubgithub.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226cGitHubgithub.com/matrix-org/synapse/releases/tag/v1.33.2GitHubgithub.com/matrix-org/synapse/security/advisories/GHSA-x345-32rc-8h85Reflists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/

How CyberStrike helps

Frequently asked questions

What is CVE-2021-29471?

CVE-2021-29471 is a low-severity vulnerability. It was published on May 11, 2021 and has a CVSS 3.1 base score of 3.7 (LOW).

How severe is CVE-2021-29471?

This vulnerability has a CVSS 3.1 base score of 3.7, rated LOW. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2021-29471?

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2021-29471?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-29471 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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