CVE-2025-61921

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.

CVSS 4.0

2.7CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U

CVSS 3.1

7.5CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

0.5% chance of exploitation in the next 30 days; higher than 42% of CVEs (scores of 2026-10-25)

CWE

CWE-1333

Published

2025-10-10

Modified

2026-10-19

Record from

the NVD, synced 2026-10-19

Affected

• sinatrarb:sinatra

Packages (OSV)

References

• https://bugs.ruby-lang.org/issues/19104
• 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/security/advisories/GHSA-mr3q-g2mv-mr4q

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