CVE-2026-63097

MEDIUM 4.3

Dendrite 0.13.8 syncapi /context Endpoint Post-Leave State Exposure

CVSS Score

4.3

EPSS Score

0.0%

EPSS Percentile

0th

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.

CWE	CWE-863
Vendor	matrix-org
Product	dendrite
Published	Jul 17, 2026

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CVSS v3 Breakdown

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

None

Affected Versions

matrix-org / dendrite

0 ≤ 0.13.8

References

NVD ↗ CVE.org ↗ EPSS Data ↗

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

Credits

George Chen