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.
History

Tue, 28 Jul 2026 02:30:00 +0000

Type Values Removed Values Added
First Time appeared Matrix
Matrix dendrite
CPEs cpe:2.3:a:matrix:dendrite:*:*:*:*:*:*:*:*
Vendors & Products Matrix
Matrix dendrite

Thu, 23 Jul 2026 21:45:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Fri, 17 Jul 2026 16:00:00 +0000

Type Values Removed Values Added
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.
Title Dendrite 0.13.8 syncapi /context Endpoint Post-Leave State Exposure
Weaknesses CWE-863
References
Metrics cvssV3_1

{'score': 4.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N'}

cvssV4_0

{'score': 5.3, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: VulnCheck

Published: 2026-07-17T15:32:45.411Z

Updated: 2026-07-28T01:50:00.775Z

Reserved: 2026-07-15T15:45:44.601Z

Link: CVE-2026-63097

cve-icon Vulnrichment

Updated: 2026-07-23T19:18:48.792Z

cve-icon NVD

No data.

cve-icon Redhat

No data.