Medium severity5.9NVD Advisory· Published Sep 13, 2021· Updated Jun 17, 2026
CVE-2021-40823
CVE-2021-40823
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.
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LLM-synthesized narrative grounded in this CVE's description and references.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
matrix-js-sdknpm | < 12.4.1 | 12.4.1 |
Affected products
3- matrix-js-sdk/matrix-js-sdkdescription
Patches
Vulnerability mechanics
References
6- github.com/advisories/GHSA-23cm-x6j7-6hq3ghsaADVISORY
- github.com/matrix-org/matrix-js-sdk/releases/tag/v12.4.1nvdThird Party AdvisoryWEB
- matrix.org/blog/2021/09/13/vulnerability-disclosure-key-sharingnvdVendor AdvisoryWEB
- nvd.nist.gov/vuln/detail/CVE-2021-40823ghsaADVISORY
- github.com/matrix-org/matrix-js-sdk/commit/894c24880da0e1cc81818f51c0db80e3c9fb2be9ghsaWEB
- github.com/matrix-org/matrix-js-sdk/security/advisories/GHSA-23cm-x6j7-6hq3ghsaWEB
News mentions
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