GHSA-6263-x97c-c4gg is a high-severity (CVSS 7.5) Improper Authentication vulnerability in matrix-js-sdk. A fix is available for matrix-js-sdk — see the affected versions and patch details below.
matrix-js-sdk subject to impersonated messages due to permissive key forwarding
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-6263-x97c-c4gg.
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.
How urgent is this, really
GHSA-6263-x97c-c4gg plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,567 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
matrix-js-sdknpmDescription
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.
Patches
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).
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].
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | matrix-js-sdk | all versions | 19.7.0npm install matrix-js-sdk@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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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-6263-x97c-c4gg 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-6263-x97c-c4gg can be triaged on real exposure rather than presence alone.
Tailored to GHSA-6263-x97c-c4gg. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 7 | thunderbird-0:102.4.0-1.el7_9 | RHSA-2022:7184 |
| Red Hat Enterprise Linux 8 | thunderbird-0:102.4.0-1.el8_6 | RHSA-2022:7190 |
| Red Hat Enterprise Linux 8.1 Update Services for SAP Solutions | thunderbird-0:102.4.0-1.el8_1 | RHSA-2022:7183 |
| Red Hat Enterprise Linux 8.2 Extended Update Support | thunderbird-0:102.4.0-1.el8_2 | RHSA-2022:7182 |
| Red Hat Enterprise Linux 8.4 Extended Update Support | thunderbird-0:102.4.0-1.el8_4 | RHSA-2022:7181 |
| Red Hat Enterprise Linux 9 | thunderbird-0:102.4.0-1.el9_0 | RHSA-2022:7178 |
Frequently Asked Questions
Is GHSA-6263-x97c-c4gg in your dependencies?
O3 Security finds GHSA-6263-x97c-c4gg across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.