CVE-2025-61921: Sinatra is vulnerable to ReDoS through ETag header value generation

CVE-2025-61921 · Severity: medium · CVSS 4 · Published 2025-10-10

Sinatra is vulnerable to ReDoS through ETag header value generation

Technologies: sinatra (RubyGems). Vendors: RubyGems.

Quick answers

Is CVE-2025-61921 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2025-61921 being exploited in the wild.
How severe is CVE-2025-61921?
Medium severity, with a CVSS score of 4, published 10 October 2025.
Which products and versions are affected?
sinatra (RubyGems) ECOSYSTEM:introduced=0,fixed=4.2.0.
Is there a fix for CVE-2025-61921?
Yes. sinatra (RubyGems): upgrade to 4.2.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
Am I affected by CVE-2025-61921?
Check whether you run sinatra (RubyGems) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • sinatra (RubyGems): upgrade to 4.2.0 or later
    bundle update sinatra

Affected products

  • sinatra (RubyGems) ECOSYSTEM:introduced=0,fixed=4.2.0

Identifiers

  • CVE-2025-61921
  • GHSA-mr3q-g2mv-mr4q

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