Matrix Client Vulnerability in Cinny Affects User Access Tokens
CVE-2026-42553

7.1HIGH

Key Information:

Vendor

Cinnyapp

Status
Cinny
Vendor
CVE Published:
27 May 2026

What is CVE-2026-42553?

Prior to version 4.10.3, Cinny, a Matrix client, was susceptible to a vulnerability that allowed remote authenticated attackers to exploit the emoji picker feature. When a victim accessed the emoji or sticker picker within a room containing a malicious emote pack, the attack could lead to the unintended transmission of the user's Matrix access token to an attacker-controlled server. This vulnerability stemmed from improper handling of user-controlled avatar metadata and deficiencies in validating URLs, creating a vector for unauthorized access. The introduction of version 4.10.3 addresses these security lapses, making it essential for users to update their applications immediately.

Affected Version(s)

cinny < 4.10.3

References

https://github.com/cinnyapp/cinny/security/advisories/GHS...
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https://github.com/cinnyapp/cinny/releases/tag/v4.10.3
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CVSS V4

Score:
7.1
Severity:
HIGH
Confidentiality:
High
Integrity:
None
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.