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Fencer Intel
high 7.5

CVE-2025-61921 json

Sinatra has ReDoS vulnerability in ETag header value generation

published last yr. modified 21d ago also EUVD-2025-33767 , GHSA-mr3q-g2mv-mr4q

cvss
7.5
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.5%
EPSS 0.5% chance of exploitation in 30 days, percentile 42%
public exploits
0
none known

Summary

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.

Patch / fix

  • rubygems sinatra 4.2.0
  • sinatrarb sinatra 4.2.0
  • ruby-sinatra Debian 12 3.0.5-3+deb12u1
  • ruby-sinatra Debian 14 4.2.1-1

debian advisories DEBIAN-CVE-2025-61921

  • ruby-sinatra Ubuntu 26.04 LTS 4.2.1-1
  • ruby-sinatra Ubuntu Pro 16.04 LTS 1.4.7-3ubuntu0.1~esm3
  • ruby-sinatra Ubuntu Pro 18.04 LTS 1.4.8-1ubuntu0.1~esm3
  • ruby-sinatra Ubuntu Pro 22.04 LTS 2.0.8.1-2+deb11u1ubuntu0.1~esm1

ubuntu advisories UBUNTU-CVE-2025-61921

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Is CVE-2025-61921 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-61921 updated cvss 5.3

sinatra: Sinatra has ReDoS vulnerability in ETag header value generation

  • Red Hat 3scale API Management Platform 2 3scale-amp21/zync, 3scale-amp22/zync, 3scale-amp24/zync, 3scale-amp25/zync, 3scale-amp26/zync, 3scale-amp2/zync-rhel7, +2 more
    affected: workaround, no fix planned “Will not fix”
  • Red Hat Enterprise Linux 8 pcs, pcs-snmp
    affected: workaround, no fix available
  • Red Hat Enterprise Linux 7 pcs, pcs-snmp, python-clufter
    not affected: vulnerable code not in execute path
  • Red Hat Enterprise Linux 9 pcs, pcs-snmp Red Hat Enterprise Linux 10 pcs
    not affected: inline mitigations already exist

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
last yr.

Exploit prediction

0.50% chance of exploitation in the next 30 days, higher than 42% of all scored CVEs (FIRST EPSS, 2026-11-09).

Exploits and checks

  • github.com https://github.com/sinatra/sinatra/pull/1823 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 2.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U
CNA 4.0 2.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
NVD 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
rubygems sinatra
<4.2.0
4.2.0

Affected products

  • sinatra sinatra

Classification

Weakness
  • CWE-1333 Inefficient Regular Expression Complexity
  • CWE-400 Uncontrolled Resource Consumption

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.