Zero-day vulnerability in Synapse

Input validation error
CVE-2025-30355

Vulnerability details

Advisory: SB2025033143 - Remote denial of service in Matrix Synapse

Vulnerable component: Synapse

CVE-ID: CVE-2025-30355

CVSSv3 score: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H/E:U/RL:O/RC:C

CWE-ID: CWE-20 - Improper input validation

Description:

The vulnerability allows a remote user to perform a denial of service (DoS) attack.

The vulnerability exists due to insufficient validation of user-supplied input. A remote user can pass specially crafted events to the application and prevent it from federating with other servers.

Note, the vulnerability is being exploited in the wild.

External links:

https://github.com/element-hq/synapse/security/advisories/GHSA-v56r-hwv5-mxg6


About zero-day vulnerabilities

Zero-day vulnerability is an undisclosed vulnerability in software that hackers can exploit to compromise computer programs, gain unauthorized access to sensitive data, penetrate networks, etc. We consider vulnerability a zero-day when there is no solution provided from software vendor and the vulnerability is being actively exploited by malicious actors.

Zero-day candidate is a potential zero-day vulnerability in software which might have been used in targeted attacks, however there is no evidence to support this suggestion.