CVE-2025-61921

Description

Sinatra is a domain-specific language for creating web applications in Ruby. In versions prior to 4.2.0, there is a denial of service vulnerability in the `If-Match` and `If-None-Match` header parsing component of Sinatra, if the `etag` method is used when constructing the response. Carefully crafted input can cause `If-Match` and `If-None-Match` header parsing in Sinatra to take an unexpected amount of time, possibly resulting in a denial of service attack vector. This header is typically involved in generating the `ETag` header value. Any applications that use the `etag` method when generating a response are impacted. Version 4.2.0 fixes the issue.

Predictions

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

References

• https://github.com/sinatra/sinatra/security/advisories/GHSA-mr3q-g2mv-mr4q
• https://nvd.nist.gov/vuln/detail/CVE-2025-61921
• https://github.com/sinatra/sinatra/issues/2120
• https://github.com/sinatra/sinatra/pull/1823
• https://github.com/sinatra/sinatra/pull/2121
• https://github.com/sinatra/sinatra/commit/3fe8c38dc405586f7ad8f2ac748aa53e9c3615bd
• https://github.com/sinatra/sinatra/commit/8ff496bd4877520599e1479d6efead39304edceb
• https://bugs.ruby-lang.org/issues/19104
• https://github.com/rubysec/ruby-advisory-db/blob/master/gems/sinatra/CVE-2025-61921.yml
• https://github.com/sinatra/sinatra
• https://security-tracker.debian.org/tracker/CVE-2025-61921