GHSA-35g4-qx3c-vjhx is a medium-severity (CVSS 6.5) Missing Authentication vulnerability in matrix-appservice-bridge. O3 Security confirms whether GHSA-35g4-qx3c-vjhx is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Automatic room upgrade handling can be used maliciously to bridge a room non-consentually
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, a proxy for how much of the ecosystem is exposed.
matrix-appservice-bridgenpmDescription
Impact
If a bridge has room upgrade handling turned on in the configuration (the roomUpgradeOpts key when instantiating a new Bridge instance.), any m.room.tombstone event it encounters will be used to unbridge the current room and bridge into the target room. However, the target room m.room.create event is not checked to verify if the predecessor field contains the previous room. This means that any mailcious admin of a bridged room can repoint the traffic to a different room without the new room being aware.
Patches
Versions 2.6.1 and greater are patched.
Workarounds
Disabling the automatic room upgrade handling can be done by removing the roomUpgradeOpts key from the Bridge class options.
References
The issue is patched by https://github.com/matrix-org/matrix-appservice-bridge/pull/330
For more information]
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Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | matrix-appservice-bridge | all versions | 2.6.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for matrix-appservice-bridge. 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-appservice-bridge to 2.6.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-35g4-qx3c-vjhx 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-35g4-qx3c-vjhx 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-35g4-qx3c-vjhx. 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-35g4-qx3c-vjhx in your dependencies?
O3 detects GHSA-35g4-qx3c-vjhx across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.