FKIE_CVE-2026-34831

Vulnerability from fkie_nvd - Published: 2026-04-02 17:16 - Updated: 2026-04-16 16:44
Severity ?
4.8 (Medium) - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
6.5 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
Summary
Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than the number of bytes actually sent on the wire. Because Rack::Files reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters. This results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect Content-Length value. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6.
References
security-advisories@github.comhttps://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388Vendor Advisory
Impacted products
Vendor Product Version
rack rack *
rack rack *
rack rack *
To clipboard 

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  "configurations": [
    {
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          "cpeMatch": [
            {
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  "cveTags": [],
  "descriptions": [
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      "lang": "en",
      "value": "Rack is a modular Ruby web server interface. Prior to versions 2.2.23, 3.1.21, and 3.2.6, Rack::Files#fail sets the Content-Length response header using String#size instead of String#bytesize. When the response body contains multibyte UTF-8 characters, the declared Content-Length is smaller than the number of bytes actually sent on the wire. Because Rack::Files reflects the requested path in 404 responses, an attacker can trigger this mismatch by requesting a non-existent path containing percent-encoded UTF-8 characters. This results in incorrect HTTP response framing and may cause response desynchronization in deployments that rely on the incorrect Content-Length value. This issue has been patched in versions 2.2.23, 3.1.21, and 3.2.6."
    }
  ],
  "id": "CVE-2026-34831",
  "lastModified": "2026-04-16T16:44:32.200",
  "metrics": {
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          "attackVector": "NETWORK",
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          "baseScore": 4.8,
          "baseSeverity": "MEDIUM",
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