AIKIDO-2026-510742
matrix-synapse is vulnerable to Information Disclosure
55
Medium Risk
This Affects:
matrix-synapseTL;DR
The federation event_auth endpoint does not verify that the requesting homeserver is joined to the room before returning authorisation events for a given event ID. A malicious remote homeserver joined to any room on the target can query authorisation events for rooms it has not joined. This discloses authorisation events across room boundaries. The fix enforces a room-membership check before responding.
Who does this affect?
You are affected if you are using a version that falls within the vulnerable range and your homeserver participates in open federation.
Background info
matrix-synapse is vulnerable to Information Disclosure in versions 0.0.1 - 1.157.1.
How to fix this
Upgrade the matrix-synapse library to the patch version.
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