CVE-2025-61921: Sinatra is a domain-specific language for creating web applications in Ruby

Q: How do I fix CVE-2025-61921?

sinatra: upgrade to 4.2.0. Exact commands for each OS are on this page.

Q: Is CVE-2025-61921 being exploited?

CVE-2025-61921 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2025-61921 affect?

CVE-2025-61921 affects sinatra. Severity is high (CVSS 7.5). 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` met

Q: How urgent is CVE-2025-61921?

Priority 47/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

This week

HIGH 7.5REMOTEUPGRADE

CVE-2025-61921 is a high-severity flaw (CVSS 7.5) affecting sinatra. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 ser

Why this priority

High severity
Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 58%)
CISA exploited list	No
Weakness	CWE-1333
Published	2025-10-10
Last modified	2026-10-19

Publisher (CNA): GitHub, Inc. · Vendor: sinatrarb

Last updated 2026-10-19 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-10-10 20:15 UTCPublished CVE record published
2026-10-19 16:10 UTCUpdated Record last modified

sinatrarb sinatra UPGRADE

Affected: < 4.2.0

Fixed in: 4.2.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy sinatra || rpm -q sinatra || sinatra --version

2. UPGRADE to 4.2.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade sinatra

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade sinatra

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-61921?

sinatra: upgrade to 4.2.0. Exact commands for each OS are on this page.

Is CVE-2025-61921 being exploited?

CVE-2025-61921 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-61921 affect?

CVE-2025-61921 affects sinatra. Severity is high (CVSS 7.5). 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` met

How urgent is CVE-2025-61921?

Priority 47/100. High severity; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

Ruby vulnerabilities

Related CVEs

CVE-2024-37116 MEDIUM 6.5 UPGRADE Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') vulnerability in s

References

← Back to latest CVEs