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CVE-2021-21394

5.3 · MEDIUM

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

Published Apr 12, 2021CWE-20EPSS 1.54%

Overview

CVE-2021-21394 is a medium-severity vulnerability. It was published on April 12, 2021 and has a CVSS 3.1 base score of 5.3 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 5.3, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is 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 1.28.0 Synapse is missing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion. Note that the groups feature is not part of the Matrix specification and the chosen maximum lengths are arbitrary. Not all clients might abide by them. Refer to referenced GitHub security advisory for additional details including workarounds.

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/pull/9321GitHubgithub.com/matrix-org/synapse/pull/9393GitHubgithub.com/matrix-org/synapse/security/advisories/GHSA-w9fg-xffh-p362Reflists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/Refpypi.org/project/matrix-synapse/GitHubgithub.com/matrix-org/synapse/pull/9321GitHubgithub.com/matrix-org/synapse/pull/9393GitHubgithub.com/matrix-org/synapse/security/advisories/GHSA-w9fg-xffh-p362Reflists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/Refpypi.org/project/matrix-synapse/

How CyberStrike helps

Frequently asked questions

What is CVE-2021-21394?

CVE-2021-21394 is a medium-severity vulnerability. It was published on April 12, 2021 and has a CVSS 3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2021-21394?

This vulnerability has a CVSS 3.1 base score of 5.3, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

How do I fix or remediate CVE-2021-21394?

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-2021-21394?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-21394 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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