CVE-2026-63097

· MEDIUMDeferred

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CVSS v3.1

4.3

CVSS v4.0

5.3

EPSS

0.27%

Published

Jul 17, 2026

Modified

Jul 23, 2026

Public PoC / Exploit (1)

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Links to public security research (Exploit-DB, Nuclei, Trickest, GitHub) for defensive use only.

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.

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N

Weaknesses (CWE)

CWE-863

References (2)

https://github.com/geo-chen/oss/blob/main/dendrite.md#finding-3-context-returns-current-room-state-to-non-members-and-left-users-history-visibility-bypass

https://www.vulncheck.com/advisories/dendrite-syncapi-context-endpoint-post-leave-state-exposure

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