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BREW-MAILCATCHER-CVE-202… (GHSA-MR3Q-G2MV-MR4Q)

Vulnerability from osv_homebrew – Published: 2026-08-13 17:11 – Updated: 2026-09-17 17:44 – Source website
VLAI
Summary
Sinatra is vulnerable to ReDoS through ETag header value generation
Details

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)
Severity
2.7 (Low)
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
References
To clipboard 

{
  "affected": [
    {
      "ecosystem_specific": {
        "fix": "bump",
        "range_state": "fixed",
        "resource": "sinatra",
        "resource_purl": "pkg:gem/sinatra@4.2.1",
        "upstream_fixed_in": "4.2.0"
      },
      "package": {
        "ecosystem": "Homebrew",
        "name": "mailcatcher",
        "purl": "pkg:brew/mailcatcher"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.8.1"
            },
            {
              "fixed": "0.11.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "confidence": "high",
    "source": "matched",
    "strategy": "registry",
    "upstream_evidence": [
      {
        "ecosystem": "RubyGems",
        "key": "pkg:gem/sinatra@4.2.1",
        "name": "sinatra",
        "resource": "sinatra",
        "strategy": "registry",
        "subject_version": "4.2.1"
      }
    ]
  },
  "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 \u003c 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 \u003e= 3.2)",
  "id": "BREW-mailcatcher-CVE-2025-61921",
  "modified": "2026-09-17T17:44:12Z",
  "published": "2026-08-13T17:11:30Z",
  "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"
    }
  ],
  "schema_version": "1.7.3",
  "severity": [
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Sinatra is vulnerable to ReDoS through ETag header value generation",
  "upstream": [
    "GHSA-mr3q-g2mv-mr4q",
    "CVE-2025-61921"
  ]
}



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