Denial of service due to incorrect application of event authorization rules

Impact

The Matrix specification specifies a list of event authorization rules which must be checked when determining if an event should be accepted into a room.

In versions of Synapse up to and including v1.61, some of these rules are not correctly applied. An attacker could craft events which would be accepted by Synapse but not a spec-conformant server, potentially causing divergence in the room state between servers.

Patches

Administrators of homeservers with federation enabled are advised to upgrade to v1.62.0 or higher.

Workarounds

• Federation can be disabled by setting federation_domain_whitelist to an empty list ([]).

References

• https://github.com/matrix-org/synapse/pull/13087
• https://github.com/matrix-org/synapse/pull/13088

For more information

If you have any questions or comments about this advisory, e-mail us at security@matrix.org.