Summary
matrix-js-sdk subject to user impersonation due to key/device identifier confusion in SAS verification
Workarounds
As this attack requires coordination between a malicious homeserver and an attacker -- if you trust your homeserver no particular workaround is needed.
As a potential way of detecting compromise, it’s possible to review your device list or the device list of other users for devices with IDs in the form of a base64 cross-signing key (5XaczGNlfz0bl8R1IX5qn+tBoue2tWJqLMh+SDUuvCk) instead of classical device ID (SEHACYDHMG).
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 could interfere with the verification flow between two users, injecting its own cross-signing user identity in place of one of the users’ identities, leading to the other device trusting/verifying the user identity under the control of the homeserver instead of the intended one.
The vulnerability is a bug in the matrix-js-sdk, caused by checking and signing user identities and devices in two separate steps, and inadequately fixing the keys to be signed between those steps.
Even though the attack is partly made possible due to the design decision of treating cross-signing user identities as Matrix devices on the server side (with their device ID set to the public part of the user identity key), no other examined implementations were vulnerable.
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-2022-39250 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.
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The matrix-js-sdk has been modified to double check that the key signed is the one that was verified instead of just referencing the key by ID. An additional check has been made to report an error when one of the device ID matches a cross-signing key.
Frequently Asked Questions
- What is CVE-2022-39250? CVE-2022-39250 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-2022-39250? CVE-2022-39250 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-2022-39250? matrix-js-sdk (npm) versions < 19.7.0 is affected.
- Is there a fix for CVE-2022-39250? Yes. CVE-2022-39250 is fixed in 19.7.0. Upgrade to this version or later.
- Is CVE-2022-39250 exploitable, and should I be worried? Whether CVE-2022-39250 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-2022-39250 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-2022-39250? Upgrade
matrix-js-sdkto 19.7.0 or later.