CVE-2025-61921

CVE-2025-61921 is a high-severity vulnerability in Sinatrarb Sinatra with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-1333.

Key facts

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.

Frequently asked questions

What is 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.
How severe is CVE-2025-61921?
CVE-2025-61921 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2025-61921 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (37th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-61921?
CVE-2025-61921 affects Sinatrarb Sinatra. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-61921?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2025-61921 have an EU (EUVD) identifier?
Yes. CVE-2025-61921 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-33767.
When was CVE-2025-61921 published?
CVE-2025-61921 was published on 2025-10-10 and last updated on 2026-06-17.

References

Affected products (1)

More vulnerabilities in Sinatrarb Sinatra

All CVEs affecting Sinatrarb Sinatra →

Other CWE-1333 vulnerabilities

Browse all CWE-1333 vulnerabilities →