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

Sinatra is vulnerable to ReDoS through ETag header value generation (CVE-2025-61921) | HOL Guard CVE

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps sinatra (rubygems). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
sinatrarubygems	>=0 <4.2.0	4.2.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for sinatra.
Review the reported fix. Update sinatra to 4.2.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Oct 10, 2025
Evidence: source:osv:source_dates:source-dates:record
Source modified
Sep 10, 2026
Evidence: source:osv:source_dates:source-dates:record
First seen by HOL
Aug 7, 2026

Sources and claim methodology

Upstream source description

### Summary 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 and you are using Ruby < 3.2. ### Details 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 if they are using Ruby below version 3.2. ### Resources * https://github.com/sinatra/sinatra/issues/2120 (report) * https://github.com/sinatra/sinatra/pull/2121 (fix) * https://github.com/sinatra/sinatra/pull/1823 (older ReDoS vulnerability) * https://bugs.ruby-lang.org/issues/19104 (fix in Ruby >= 3.2)

Quoted source text, attributed separately from HOL analysis.