Improper Access Control Vulnerability in Dendrite Product by Matrix.org
CVE-2026-63097

5.3MEDIUM

Key Information:

Vendor

Matrix-org

Status
Dendrite
Vendor
CVE Published:
17 July 2026

Badges

👾 Exploit Exists🟡 Public PoC

What is CVE-2026-63097?

An improper access control issue has been identified in Dendrite versions up to 0.13.8, specifically affecting the syncapi /context endpoint. This vulnerability allows authenticated local users, particularly those who have exited a room, to exploit a flawed membership evaluation. The vulnerability arises because the access checks rely solely on the RoomExists field, while overlooking critical indicators such as IsInRoom, HasBeenInRoom, and Membership. By exploiting this weakness, attackers can retrieve unfiltered current room states that should normally be restricted, enabling them to access sensitive post-leave room state events previously withheld by the /messages and /sync endpoints.

Affected Version(s)

dendrite 0 <= 0.13.8

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2026-63097 - Proof of Concept

References

https://github.com/geo-chen/oss/blob/main/dendrite.md#fin...
technical-descriptionexploit
https://www.vulncheck.com/advisories/dendrite-syncapi-con...
third-party-advisory

CVSS V4

Score:
5.3
Severity:
MEDIUM
Confidentiality:
Low
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

Credit

George Chen
.