Summary
matrix-js-sdk subject to impersonated messages due to permissive key forwarding
Workarounds
As this attack requires coordination between a malicious homeserver and an attacker, if you trust your homeserver, no particular workaround is needed.
References
For more information
If you have any questions or comments about this advisory, e-mail us at [email protected].
Impact
An attacker cooperating with a malicious homeserver can construct messages appearing to have come from another person. Such messages will be marked with a grey shield on some platforms, but this may be missing in others.
This attack is possible due to the matrix-js-sdk implementing a too permissive key forwarding strategy on the receiving end.
Key forwarding is a mechanism allowing clients to recover from “unable to decrypt” messages when they missed the initial key distribution, at the time the message was originally sent. Examples include accessing message history before they joined the room but also when some network/federation errors have occurred.
The application does not adequately verify the identity of a user, device, or process before granting access. Typical impact: unauthorized access to functions or data reserved for authenticated parties.
CVE-2022-39249 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (19.7.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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The default policy for accepting key forwards has been made more strict in the matrix-js-sdk. matrix-js-sdk will now only accept forwarded keys in response to previously issued requests and only from own, verified devices.
A unique exception to this rule is with the experimental MSC3061, that is forwarding room keys for past messages when invited in a room configured with the proper history visibility setting. Such key forwards are parked upon receipt and are only accepted if the SDK receives an invitation for that room from the inviter in a limited time window.
The SDK now sets a trusted flag on the decrypted message upon decryption, based on whether the key used to decrypt the message was received from a trusted source. Clients need to ensure that messages decrypted with a key with trusted = false are decorated appropriately (for example, by showing a warning for such messages).
Frequently Asked Questions
- What is CVE-2022-39249? CVE-2022-39249 is a high-severity improper authentication vulnerability in matrix-js-sdk (npm), affecting versions < 19.7.0. It is fixed in 19.7.0. The application does not adequately verify the identity of a user, device, or process before granting access.
- How severe is CVE-2022-39249? CVE-2022-39249 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of matrix-js-sdk are affected by CVE-2022-39249? matrix-js-sdk (npm) versions < 19.7.0 is affected.
- Is there a fix for CVE-2022-39249? Yes. CVE-2022-39249 is fixed in 19.7.0. Upgrade to this version or later.
- Is CVE-2022-39249 exploitable, and should I be worried? Whether CVE-2022-39249 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2022-39249 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2022-39249? Upgrade
matrix-js-sdkto 19.7.0 or later.