Summary
matrix-js-sdk subject to user spoofing via Olm/Megolm protocol confusion
Workarounds
As this attack requires coordination between a malicious home server and an attacker, if you trust your home server no particular workaround is needed. Notice that the backup spoofing attack is a particularly sophisticated targeted attack.
We are not aware of this attack being used in the wild, though specifying a false positive-free way of noticing malicious key backups key is challenging.
As an abundance of caution, to avoid malicious backup attacks, you should not verify your new logins using emoji/QR verifications methods until patched. Prefer verifying with your security passphrase instead.
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 that legitimately appear to have come from another person, without any indication such as a grey shield.
Additionally, a sophisticated attacker cooperating with a malicious homeserver could employ this vulnerability to perform a targeted attack in order to send fake to-device messages appearing to originate from another user. This can allow, for example, to inject the key backup secret during a self-verification, to make a targeted device start using a malicious key backup spoofed by the homeserver.
These attacks are possible due to a protocol confusion vulnerability that accepts to-device messages encrypted with Megolm instead of Olm.
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-2022-39251 has a CVSS score of 8.6 (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.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
matrix-js-sdk has been modified to only accept Olm-encrypted to-device messages.
Out of caution, several other checks have been audited or added:
- Cleartext
m.room_key,m.forwarded_room_keyandm.secret.sendto_device messages are discarded. - Secrets received from untrusted devices are discarded.
- Key backups are only usable if they have a valid signature from a trusted device (no more local trust, or trust-on-decrypt).
- The origin of a to-device message should only be determined by observing the Olm session which managed to decrypt the message, and not by using claimed sender_key, user_id, or any other fields controllable by the homeserver.
Frequently Asked Questions
- What is CVE-2022-39251? CVE-2022-39251 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-2022-39251? CVE-2022-39251 has a CVSS score of 8.6 (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-2022-39251? matrix-js-sdk (npm) versions < 19.7.0 is affected.
- Is there a fix for CVE-2022-39251? Yes. CVE-2022-39251 is fixed in 19.7.0. Upgrade to this version or later.
- Is CVE-2022-39251 exploitable, and should I be worried? Whether CVE-2022-39251 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-2022-39251 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-2022-39251? Upgrade
matrix-js-sdkto 19.7.0 or later.