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CVE-2025-61921

Sinatrarb Sinatra vulnerability

7.5 HIGHPublic exploitEPSS 0.50%
  1. Published10 Oct 2025

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityNone
IntegrityNone
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

Sinatrarb Sinatra< 4.2.0

Remediation

Fixed in
Sinatrarb Sinatra≥ 4.2.0

References

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Frequently asked

Is CVE-2025-61921 being actively exploited?

CVE-2025-61921 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.50%.

How severe is CVE-2025-61921?

CVE-2025-61921 has a CVSS 3.1 base score of 7.5, rated high. EPSS estimates a 0.50% probability of exploitation.

Which products are affected by CVE-2025-61921?

Affected products include Sinatrarb Sinatra.

How do I fix CVE-2025-61921?

Upgrade affected software to a fixed version, for example Sinatrarb Sinatra 4.2.0 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.