Input validation error in Synapse - #VU139986
Published: July 29, 2026
Vulnerability identifier: #VU139986
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: N/A
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Affected software:
Synapse
Synapse
Detailed vulnerability description
The vulnerability allows a remote attacker to evade external rate-limiting.
The vulnerability exists due to improper input validation in HTTP request path handling when processing crafted request paths with extraneous path segments. A remote attacker can send a specially crafted request to evade external rate-limiting.
The Client-Server API, Federation API, Synapse Admin API, and Key Server API are not affected by this issue.
Remediation
Install security update from vendor's website.