CVE-2026-63097Dendrite 0.13.8 syncapi /context Endpoint Post-Leave State Exposure

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.

Data: CVE.org, NVD, CISA KEV, FIRST EPSS, Ubuntu. Published as the sources state it, in English.

Affected products and versions

References and patches

• Researcher Disclosure technical-descriptionexploit
• https://www.vulncheck.com/advisories/dendrite-syncapi-context-endpoint-post-leave-state-exposure third-party-advisory