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CVE-2026-34831

Estado: AnalizadaMedia (6.5)—

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.

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

Tecnologías afectadas (1)

Rack — Rack

CWE

Referencias

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{
  "id": "CVE-2026-34831",
  "cveTags": [],
  "metrics": {
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-34831",
          "role": "CISA Coordinator",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "version": "2.0.3",
          "timestamp": "2026-04-03T17:43:52.462237Z"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "security-advisories@github.com",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 4.8,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N",
          "integrityImpact": "LOW",
          "userInteraction": "NONE",
          "attackComplexity": "HIGH",
          "availabilityImpact": "NONE",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "LOW"
        },
        "impactScore": 2.5,
        "exploitabilityScore": 2.2
      },
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 6.5,
          "attackVector": "NETWORK",
          "baseSeverity": "MEDIUM",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N",
          "integrityImpact": "LOW",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "NONE",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "LOW"
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        "exploitabilityScore": 3.9
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  "affected": [
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          "vendor": "rack",
          "product": "rack",
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              "version": "< 2.2.23"
            },
            {
              "status": "affected",
              "version": ">= 3.0.0.beta1, < 3.1.21"
            },
            {
              "status": "affected",
              "version": ">= 3.2.0, < 3.2.6"
            }
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  "published": "2026-04-02T17:16:26.420",
  "references": [
    {
      "url": "https://github.com/rack/rack/security/advisories/GHSA-q2ww-5357-x388",
      "tags": [
        "Vendor Advisory"
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      "source": "security-advisories@github.com"
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  ],
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "type": "Secondary",
      "source": "security-advisories@github.com",
      "description": [
        {
          "lang": "en",
          "value": "CWE-130"
        },
        {
          "lang": "en",
          "value": "CWE-135"
        }
      ]
    }
  ],
  "descriptions": [
    {
      "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."
    },
    {
      "lang": "es",
      "value": "Rack es una interfaz modular de servidor web Ruby. Antes de las versiones 2.2.23, 3.1.21 y 3.2.6, Rack::Files#fail establece el encabezado de respuesta Content-Length usando String#size en lugar de String#bytesize. Cuando el cuerpo de la respuesta contiene caracteres UTF-8 multibyte, el Content-Length declarado es menor que el número de bytes realmente enviados por la red. Debido a que Rack::Files refleja la ruta solicitada en las respuestas 404, un atacante puede desencadenar esta discrepancia solicitando una ruta inexistente que contenga caracteres UTF-8 codificados por porcentaje. Esto resulta en un encuadre incorrecto de la respuesta HTTP y puede causar desincronización de la respuesta en implementaciones que dependen del valor incorrecto de Content-Length. Este problema ha sido parcheado en las versiones 2.2.23, 3.1.21 y 3.2.6."
    }
  ],
  "lastModified": "2026-07-24T21:10:00.143",
  "configurations": [
    {
      "nodes": [
        {
          "negate": false,
          "cpeMatch": [
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  "sourceIdentifier": "security-advisories@github.com"
}