CVE-2026-63097 Dendrite 0.13.8 syncapi /context Endpoint Post-Leave State Exposure
Authenticated users who left a room can access current room state via the syncapi context endpoint, bypassing membership checks.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-63097?
CVE-2026-63097 is a medium-severity missing authorization vulnerability in matrix-org dendrite, published on 17 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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.
Weakness: CWE-863
Which versions are affected by CVE-2026-63097?
How do I fix CVE-2026-63097?
No fix has been published for CVE-2026-63097 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-63097 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-63097 exists.
Sources
Also known as GHSA-xq7h-2f2w-f2xq.