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National Vulnerability Database

National Vulnerability Database

NVD

National Vulnerability Database
  1. Vulnerabilities

CVE-2026-42553 Detail

Description

Cinny is a Matrix client. Prior to 4.10.3, A remote authenticated attacker who shares a room with a victim and has permissions to create room emotes (for example in a DM) can cause the victim's client to send their Matrix access token to an attacker-controlled server. This occurs when the victim opens the emoji or sticker picker for the room containing a malicious emote pack. This is caused by an incorrect fallback in EmojiBoard that uses untrusted pack.meta.avatar (user-controlled) without converting/validating it as an MXC URL, allowing arbitrary HTTP(S) URLs to be used. Also, the service worker attaching the user's Authorization bearer token to all outbound GET requests whose URL contains /_matrix/client/v1/media/download or /_matrix/client/v1/media/thumbnail without verifying the request host matches the configured homeserver origin. An attacker-controlled URL containing those path fragments and permissive CORS will receive the victim's Authorization header (access token). This vulnerability is fixed in 4.10.3.


Metrics

 
NVD enrichment efforts reference publicly available information to associate vector strings. CVSS information contributed by other sources is also displayed.
CVSS 4.0 Severity and Vector Strings:

NIST CVSS score
NIST: NVD
N/A
NVD assessment not yet provided.

Nist CVSS score does not match with CNA score
CNA:  GitHub, Inc.
CVSS-B 7.1 HIGH
Vector:  CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

References to Advisories, Solutions, and Tools

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URL Source(s) Tag(s)
https://github.com/cinnyapp/cinny/releases/tag/v4.10.3 GitHub, Inc.
https://github.com/cinnyapp/cinny/security/advisories/GHSA-j944-w549-3453 GitHub, Inc.

Weakness Enumeration

CWE-ID CWE Name Source
CWE-20 Improper Input Validation GitHub, Inc.  

Change History

1 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2026-42553
NVD Published Date:
05/27/2026
NVD Last Modified:
05/27/2026
Source:
GitHub, Inc.