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CVE-2026-43966

Estado: AnalizadaMedia (6.3)—

Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') vulnerability in ninenines cowlib allows HTTP response splitting via non-VCHAR bytes in structured-fields string values.

cow_http_struct_hd:escape_string/2 in cowlib only escapes \ and ", passing all other bytes through verbatim. This creates an encoder/decoder asymmetry: the matching parser accepts only printable ASCII (0x20–0x7E, excluding " and \), but the encoder emits any byte including CR and LF.

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An application that builds a structured HTTP header via cow_http_struct_hd:item/1 (or a higher-level wrapper such as cow_http_hd:wt_protocol/1) from attacker-controlled input can have \r\n injected into the serialized header value. Once on the wire, the injected CRLF terminates the current header and any following bytes are interpreted as a new header, enabling HTTP response splitting.

This issue affects cowlib from 2.9.0.

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)

Ninenines — Cowlib

CWE

Referencias

JSON original (NVD)

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      "source": "6b3ad84c-e1a6-4bf7-a703-f496b71e49db"
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    {
      "lang": "en",
      "value": "Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') vulnerability in ninenines cowlib allows HTTP response splitting via non-VCHAR bytes in structured-fields string values.\n\ncow_http_struct_hd:escape_string/2 in cowlib only escapes \\ and \", passing all other bytes through verbatim. This creates an encoder/decoder asymmetry: the matching parser accepts only printable ASCII (0x20–0x7E, excluding \" and \\), but the encoder emits any byte including CR and LF. An application that builds a structured HTTP header via cow_http_struct_hd:item/1 (or a higher-level wrapper such as cow_http_hd:wt_protocol/1) from attacker-controlled input can have \\r\\n injected into the serialized header value. Once on the wire, the injected CRLF terminates the current header and any following bytes are interpreted as a new header, enabling HTTP response splitting.\n\nThis issue affects cowlib from 2.9.0."
    },
    {
      "lang": "es",
      "value": "La vulnerabilidad de Neutralización Incorrecta de Secuencias CRLF en Encabezados HTTP ('División de Solicitud/Respuesta HTTP') en ninenines cowlib permite la división de respuesta HTTP a través de bytes no VCHAR en valores de cadena de campos estructurados.\n\ncow_http_struct_hd:escape_string/2 en cowlib solo escapa \\ y \", pasando todos los demás bytes textualmente. Esto crea una asimetría de codificador/decodificador: el analizador coincidente acepta solo ASCII imprimible (0x20-0x7E, excluyendo \" y \\), pero el codificador emite cualquier byte, incluidos CR y LF. Una aplicación que construye un encabezado HTTP estructurado a través de cow_http_struct_hd:item/1 (o un envoltorio de nivel superior como cow_http_hd:wt_protocol/1) desde una entrada controlada por el atacante puede tener \\r\\n inyectado en el valor del encabezado serializado. Una vez en la red, el CRLF inyectado termina el encabezado actual y cualquier byte siguiente se interpreta como un nuevo encabezado, lo que permite la división de respuesta HTTP.\n\nEste problema afecta a cowlib desde la versión 2.9.0."
    }
  ],
  "lastModified": "2026-08-17T17:56:14.473",
  "configurations": [
    {
      "nodes": [
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