CVE-2025-61921: Sinatra Denial of Service Vulnerability

Q: What is CVE-2025-61921?

CVE-2025-61921 is a security vulnerability in Sinatra involving Sinatra is vulnerable to ReDoS through ETag header value generation under CWE-400: Uncontrolled Resource Consumption.

Q: Which Sinatra versions are affected?

Affected versions include releases prior to 4.2.0 across affected packages: sinatra.

Q: What version fixes CVE-2025-61921?

Upgrading to 4.2.0 (or the latest patched release for your respective branch) resolves the vulnerability.

Q: Is sinatra affected?

Yes, sinatra is affected in releases prior to 4.2.0. Upgrade your dependency to 4.2.0 or later.

Q: What CWE is associated with CVE-2025-61921?

CVE-2025-61921 is classified under CWE-400: Uncontrolled Resource Consumption (The product does not properly control the allocation and maintenance of a limited resource.).

Q: How can I check RubyGems dependencies for CVE-2025-61921?

Run the dependency tree command: 'inspect dependencies for sinatra'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

LOW

Advisory Identifier: GHSA-mr3q-g2mv-mr4q

CWE-400 CWE-1333

Published 2025-10-10

Advisory Summary

CVE-2025-61921 is a LOW denial of service vulnerability (CWE-400: Uncontrolled Resource Consumption) affecting Sinatra libraries in the RubyGems ecosystem. The issue involves sinatra is vulnerable to redos through etag header value generation. Remediation is available by upgrading affected packages to version 4.2.0.

CVE-2025-61921 at a Glance

CVE Identifier CVE-2025-61921

GHSA Identifier GHSA-mr3q-g2mv-mr4q

Severity LOW

CVSS v3.1 Base Score N/A

CWE Classification CWE-400: Uncontrolled Resource Consumption

Affected Product Sinatra

Package Ecosystem RubyGems

Published Date 2025-10-10

Last Updated 2025-10-13

How to Fix CVE-2025-61921

To remediate this vulnerability, upgrade all affected Sinatra dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

sinatra fixed: 4.2.0

Upgrade sinatra to 4.2.0

Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release:

inspect dependencies for sinatra

How to Check if You Are Affected

To determine whether your application is affected by CVE-2025-61921, inspect your project dependencies for Sinatra:

inspect dependencies for sinatra

Analyze the terminal output to locate any version of Sinatra in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.2.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-400: Uncontrolled Resource Consumption, where the product does not properly control the allocation and maintenance of a limited resource. In Sinatra, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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)

CVE-2025-61921 Affected Sinatra Versions

1 component(s)

Fixed Versions:

4.2.0

Product / Package	Ecosystem	Affected Versions	Fixed Version
sinatra gem/sinatra	RubyGems	< 4.2.0	4.2.0

References

GitHub Advisory / Wiki ADVISORY

https://github.com/sinatra/sinatra/security/advisories/GHSA-mr3q-g2mv-mr4q

NVD — CVE-2025-61921 NVD

https://nvd.nist.gov/vuln/detail/CVE-2025-61921

Sinatra Source Repository REPOSITORY

https://github.com/sinatra/sinatra/issues/2120

Sinatra Source Repository REPOSITORY

https://github.com/sinatra/sinatra/pull/1823

Sinatra Source Repository REPOSITORY

https://github.com/sinatra/sinatra/pull/2121

Security Fix Commit FIX COMMIT

https://github.com/sinatra/sinatra/commit/3fe8c38dc405586f7ad8f2ac748aa53e9c3615bd

Security Fix Commit FIX COMMIT

https://github.com/sinatra/sinatra/commit/8ff496bd4877520599e1479d6efead39304edceb

bugs.ruby-lang.org/issues/19104 WEB

https://bugs.ruby-lang.org/issues/19104

Sinatra Source Repository REPOSITORY

https://github.com/rubysec/ruby-advisory-db/blob/master/gems/sinatra/CVE-2025-61921.yml

Sinatra Source Repository REPOSITORY

https://github.com/sinatra/sinatra

Frequently Asked Questions

What is CVE-2025-61921?

CVE-2025-61921 is a security vulnerability in Sinatra involving Sinatra is vulnerable to ReDoS through ETag header value generation under CWE-400: Uncontrolled Resource Consumption.

Which Sinatra versions are affected?

Affected versions include releases prior to 4.2.0 across affected packages: sinatra.

What version fixes CVE-2025-61921?

Upgrading to 4.2.0 (or the latest patched release for your respective branch) resolves the vulnerability.

Is sinatra affected?

Yes, sinatra is affected in releases prior to 4.2.0. Upgrade your dependency to 4.2.0 or later.

What CWE is associated with CVE-2025-61921?

CVE-2025-61921 is classified under CWE-400: Uncontrolled Resource Consumption (The product does not properly control the allocation and maintenance of a limited resource.).

How can I check RubyGems dependencies for CVE-2025-61921?

Run the dependency tree command: 'inspect dependencies for sinatra'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.

Machine-readable OSV JSON OSV v1.5 Schema

Normalized schema output

View Raw JSON

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-mr3q-g2mv-mr4q",
  "modified" : "2025-10-13T15:46:28Z",
  "published" : "2025-10-10T20:28:47Z",
  "aliases" : [ "CVE-2025-61921" ],
  "summary" : "Sinatra is vulnerable to ReDoS through ETag header value generation",
  "details" : "### Summary\n\nThere 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.\n\n### Details\n\nCarefully 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.\n\n### Resources\n\n* https://github.com/sinatra/sinatra/issues/2120 (report)\n* https://github.com/sinatra/sinatra/pull/2121 (fix)\n* https://github.com/sinatra/sinatra/pull/1823 (older ReDoS vulnerability)\n* https://bugs.ruby-lang.org/issues/19104 (fix in Ruby >= 3.2)",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "RubyGems",
      "name" : "sinatra"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.2.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/sinatra/sinatra/security/advisories/GHSA-mr3q-g2mv-mr4q"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2025-61921"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sinatra/sinatra/issues/2120"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sinatra/sinatra/pull/1823"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sinatra/sinatra/pull/2121"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sinatra/sinatra/commit/3fe8c38dc405586f7ad8f2ac748aa53e9c3615bd"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/sinatra/sinatra/commit/8ff496bd4877520599e1479d6efead39304edceb"
  }, {
    "type" : "WEB",
    "url" : "https://bugs.ruby-lang.org/issues/19104"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/rubysec/ruby-advisory-db/blob/master/gems/sinatra/CVE-2025-61921.yml"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/sinatra/sinatra"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1333", "CWE-400" ],
    "severity" : "LOW",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-10-10T20:28:47Z",
    "nvd_published_at" : "2025-10-10T20:15:38Z"
  }
}

CVSS V4

N/A LOW

Attack Vector N/A

Attack Complexity N/A

Privileges Required N/A

User Interaction N/A

Scope N/A

Confidentiality N/A

Integrity N/A

Availability N/A

Vector String

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

Advisory Metadata

Source ID: GHSA-mr3q-g2mv-mr4q
Schema Version: 1.4.0
Published: 2025-10-10 20:28
Last Modified: 2025-10-13 15:46
Database Record File: advisories/github-reviewed/2025/10/GHSA-mr3q-g2mv-mr4q/GHSA-mr3q-g2mv-mr4q.json