GHSA-45cj-f97f-ggwv
MEDIUMSynapse does not apply enough checks to servers requesting auth events of events in a room
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-synapseReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Impact
Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. The Matrix Federation API allows remote homeservers to request the authorisation events of events in a room. This is necessary so that a homeserver receiving some events can validate that those events are legitimate and permitted in their room. However, in versions of Synapse up to and including 1.68.0, a Synapse homeserver answering a query for authorisation events does not sufficiently check that the requesting server should be able to access them.
Authorisation events include power level events (the list of user IDs and their power levels at the time) and relevant membership events (including the display name of the sender of that event), as well as events like m.room.create, m.room.third_party_invite and m.room.join_rules. Non-authorisation events are unaffected, so it isn't possible to e.g. extract message contents this way.
This issue is only exploitable when a malicious actor knows the ID of a target room and the ID of an event from that room. In most cases, this makes exploitation infeasible. This issue is of negligible consequence for public rooms given that any server can easily join the room in order to be allowed to view authorisation events. Further, deployments in a closed federation where all homeservers are trustworthy are not affected.
Patches
The issue was patched in Synapse 1.69.0. Homeserver administrators are advised to upgrade.
Workarounds
Synapse can be configured with a list of servers that it is allowed to federate with federation_domain_whitelist. If this list is in use and all the servers on the list are trusted not to exploit this issue, then this issue is of no consequence.
This workaround is not practical for homeservers participating in open federation as interaction with any server not on the list would have to happen indirectly through servers that are, leading to inconsistent delays in message delivery.
References
Fixed in https://github.com/matrix-org/synapse/pull/13823.
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 |
|---|---|---|---|
| 🐍PyPI | matrix-synapse | all versions | 1.69.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for matrix-synapse. 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-synapse to 1.69.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-45cj-f97f-ggwv 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-45cj-f97f-ggwv 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-45cj-f97f-ggwv. 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-45cj-f97f-ggwv in your dependencies?
O3 detects GHSA-45cj-f97f-ggwv across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.