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Vulnerabilities

Vulnerability · CVE-2025-61921

Sinatra is a domain-specific language for creating web applications in Ruby.

Published Oct 10, 2025 · catalog updated Oct 10, 2025 · Sinatra is a domain-specific

Last checked Nov 4, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2025-61921. EPSS is 0.50%. Act only if a listed version of Sinatra is a domain-specific is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (Sinatra is a domain-specific).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Low2.7
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.50%
Remediation
Version ranges on file
Affected products
vendor sinatra sinatra < 4.2.0

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 and header parsing component of Sinatra, if the method is used when constructing the response. Carefully crafted input can cause and 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 header value. Any applications that use the method when generating a response are impacted. Version 4.2.0 fixes the issue.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor sinatra sinatra < 4.2.0< 4.2.0

How to fix CVE-2025-61921

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2025-61921. EPSS is 0.50%. Act only if a listed version of Sinatra is a domain-specific is installed.

Which versions are affected?

Compare what you have installed with sinatra sinatra < 4.2.0 < 4.2.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.50%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 10, 2025 · EUVD

    Detected

    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 and header parsing component of Sinatra, if the method is used when constructing the response. Carefully crafted input can cause and header parsing in Sinatra to take an unexpected amount of time, possibly resulting in a denial of service attack

  2. Oct 10, 2025 · EUVD

    Updated

    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 and header parsing component of Sinatra, if the method is used when constructing the response. Carefully crafted input can cause and header parsing in Sinatra to take an unexpected amount of time, possibly resulting in a denial of service attack

Sources

  • CVE.orgVulnerability recordCVE-2025-61921

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2025-61921

    30-day exploitation probability 0.50%

    first.org
  • EUVDVulnerability recordEUVD-2025-33767

    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 and header parsing component of Sinatra, if the method is used when constructing the response. Carefully crafted input can ca

    euvd.enisa.europa.eu

References

Freshness

Last verified in this catalog Nov 4, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSNov 4, 2026
  • CVE.orgOct 23, 2026
  • EUVDOct 23, 2026