CVE-2026-63097: Matrix-Org Dendrite

Medium severity, CVSS 4.3. EPSS: 0.3% chance of exploitation in the next 30 days.

Dendrite through 0.13.8 contains an improper access control vulnerability in the syncapi /context endpoint (syncapi/routing/context.go) that allows authenticated local users to access post-leave room state events by exploiting a flawed membership check that evaluates only the RoomExists field while ignoring IsInRoom, HasBeenInRoom, and Membership fields. Attackers who have left a room can call the rooms context API endpoint for a previously permitted event and receive unfiltered current room state that the /messages and /sync endpoints correctly withhold.

Affected products

• Matrix-Org Dendrite: up to and including 0.13.8

Published 2026-07-17. Last modified 2026-07-23.