CVE-2021-40823: Infoleak
First published: Mon Sep 13 2021(Updated: )
### Impact A logic error in the room key sharing functionality of matrix-js-sdk before 12.4.1 allows a malicious Matrix homeserver† participating in an encrypted room to steal room encryption keys from affected Matrix clients participating in that room. This allows the homeserver to decrypt end-to-end encrypted messages sent by affected clients. † Or anyone with access to the account of the original recipient of an encrypted message. Known clients affected (via their use of vulnerable versions of matrix-js-sdk): - Element Web (1.8.2 and earlier) - Element Desktop (1.8.2 and earlier) - SchildiChat Web (1.7.32-sc1 and earlier) - SchildiChat Desktop (1.7.32-sc1 and earlier) - Cinny (1.2.0 and earlier) ### Patch This was fixed in https://github.com/matrix-org/matrix-js-sdk/commit/894c24880da0e1cc81818f51c0db80e3c9fb2be9. ### Workarounds To prevent a homeserver from being able to steal the room keys, vulnerable clients can be taken offline or signed out. If signing out, care should be taken to either set up Secure Backup or export E2E room keys in order to preserve access to past messages.
Credit: cve@mitre.org cve@mitre.org cve@mitre.org
| Affected Software | Affected Version | How to fix |
|---|---|---|
| Matrix Javascript SDK | <12.4.1 |
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Reference Links
Frequently Asked Questions
What is CVE-2021-40823?
CVE-2021-40823 is a vulnerability in the room key sharing functionality of matrix-js-sdk (aka Matrix Javascript SDK) before version 12.4.1.
What is the impact of CVE-2021-40823?
The vulnerability allows a malicious Matrix homeserver to steal room encryption keys from affected Matrix clients participating in an encrypted room.
How can a malicious Matrix homeserver exploit CVE-2021-40823?
A malicious Matrix homeserver can exploit the vulnerability by participating in an encrypted room and stealing room encryption keys from affected Matrix clients.
What is the severity of CVE-2021-40823?
The severity of CVE-2021-40823 is medium with a CVSS severity score of 5.9.
How can I fix CVE-2021-40823?
To fix CVE-2021-40823, update to version 12.4.1 or later of matrix-js-sdk.
- collector/github-advisory
- alias/GHSA-23cm-x6j7-6hq3
- alias/CVE-2021-40823
- collector/github-advisory-latest
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- collector/mitre-cve
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