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.

Read the notes from the security team

• How can I get the fixes?
• What do statuses mean?
• Patch details

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Notes

Patch details

Severity score breakdown

CVSS version: CVSS v4.0 CVSS v4.0 CVSS v3.0

References

• MITRE
• NVD
• Launchpad
• Debian

Related Ubuntu Security Notices (USN)

• USN-8624-1
• Sinatra vulnerability
• 29 July 2026

Other references

• https://www.cve.org/CVERecord?id=CVE-2025-61921
• https://github.com/sinatra/sinatra/security/advisories/GHSA-mr3q-g2mv-mr4q