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CVE-2026-63097

Dendrite 0.13.8 syncapi /context Endpoint Post-Leave State Exposure

Published: Jul 17, 2026Updated: Jul 23, 2026 Sources: CVE List NVDCWE-863
4.3MEDIUM
NVD MITRE
EPSS Score
0.2%
Top 94.4%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
No Fix Available
Self-Check
Not available

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.

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:LPR:LUI:NS:UC:LI:NA:N
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:LPrivileges Required
Low
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:LConfidentiality
Low
I:NIntegrity
None
A:NAvailability
None
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Weaknesses

CWE-863

Affected Products

matrix-org
oss-project·DEaka matrix appservice irc, matrix-js-sdk, synapse
dendriteOn-prem
Communications / messaging-chat

Exploitability

No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.

Attack Graph

Products CVE Techniques Tactics

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MITRE ATT&CK

2 techniques
Initial Access
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References

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

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