Incorrect Regular Expression in Sinatra - CVE-2025-61921
Published: October 13, 2025
Vulnerability identifier: #VU116912
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
CVE-ID: CVE-2025-61921
CWE-ID: CWE-185
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.
The vulnerability exists due to insufficient input validation when processing regular expressions in ETag generation within the If-Match and If-None-Match header parsing component. A remote attacker can pass specially crafted data to the application and perform regular expression denial of service (ReDos) attack.
Affected software
Sinatra
Ubuntu
ruby-sinatra (Ubuntu package)
Ubuntu
ruby-sinatra (Ubuntu package)
How to mitigate CVE-2025-61921
Install updates from vendor's website.
Sinatra - update to 4.2.0
ruby-sinatra (Ubuntu package) - addressed in versions 1.4.7-3ubuntu0.1~esm3, 1.4.8-1ubuntu0.1~esm3, 2.0.8.1-1ubuntu0.1~esm3, 2.0.8.1-2+deb11u1ubuntu0.1~esm1
ruby-sinatra (Ubuntu package) - addressed in versions 1.4.7-3ubuntu0.1~esm3, 1.4.8-1ubuntu0.1~esm3, 2.0.8.1-1ubuntu0.1~esm3, 2.0.8.1-2+deb11u1ubuntu0.1~esm1