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CVE-2021-40823

5.9 · MEDIUM

A logic error in the room key sharing functionality of matrix-js-sdk (aka Matrix Javascript SDK) before 12.4.1 allows a malicious Matrix homeserver present in an encrypted room to steal room encryp…

Published Sep 13, 2021CWE-290EPSS 0.66%

Overview

CVE-2021-40823 is a medium-severity vulnerability. It was published on September 13, 2021 and has a CVSS 3.1 base score of 5.9 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 5.9, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical description

A logic error in the room key sharing functionality of matrix-js-sdk (aka Matrix Javascript SDK) before 12.4.1 allows a malicious Matrix homeserver present in an encrypted room to steal room encryption keys (via crafted Matrix protocol messages) that were originally sent by affected Matrix clients participating in that room. This allows the homeserver to decrypt end-to-end encrypted messages sent by affected clients.

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/matrix-js-sdk/releases/tag/v12.4.1Refmatrix.org/blog/2021/09/13/vulnerability-disclosure-key-sharingGitHubgithub.com/matrix-org/matrix-js-sdk/releases/tag/v12.4.1Refmatrix.org/blog/2021/09/13/vulnerability-disclosure-key-sharing

How CyberStrike helps

Frequently asked questions

What is CVE-2021-40823?

CVE-2021-40823 is a medium-severity vulnerability. It was published on September 13, 2021 and has a CVSS 3.1 base score of 5.9 (MEDIUM).

How severe is CVE-2021-40823?

This vulnerability has a CVSS 3.1 base score of 5.9, rated MEDIUM. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2021-40823?

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-2021-40823?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2021-40823 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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