CVE-2023-32323: Matrix Synapse

Medium severity, CVSS 4.3. EPSS: 1% chance of exploitation in the next 30 days.

Synapse is an open-source Matrix homeserver written and maintained by the Matrix.org Foundation. A malicious user on a Synapse homeserver X with permission to create certain state events can disable outbound federation from X to an arbitrary homeserver Y. Synapse instances with federation disabled are not affected. In versions of Synapse up to and including 1.73, Synapse did not limit the size of `invite_room_state`, meaning that it was possible to create an arbitrarily large invite event. Synapse 1.74 refuses to create oversized `invite_room_state` fields. Server operators should upgrade to Synapse 1.74 or newer urgently.

Affected products

• Matrix Synapse: before 1.74.0 (fixed in 1.74.0)

Published 2023-05-26. Last modified 2026-06-17.