GHSA-r48r-j8fx-mq2c
HIGHmatrix-js-sdk subject to user spoofing via Olm/Megolm protocol confusion
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Blast Radius
matrix-js-sdkReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.
Description
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.
Patches
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.
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].
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | matrix-js-sdk | all versions | 19.7.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for matrix-js-sdk. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update matrix-js-sdk to 19.7.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-r48r-j8fx-mq2c is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-r48r-j8fx-mq2c is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-r48r-j8fx-mq2c. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-r48r-j8fx-mq2c in your dependencies?
O3 detects GHSA-r48r-j8fx-mq2c across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.