CVE-2026-27959

Estado: ModificadaAlta (7.5)—

Koa is middleware for Node.js using ES2017 async functions. Prior to versions 3.1.2 and 2.16.4, Koa's `ctx.hostname` API performs naive parsing of the HTTP Host header, extracting everything before the first colon without validating the input conforms to RFC 3986 hostname syntax. When a malformed Host header containing a `@` symbol is received, `ctx.hostname` returns `evil[.]com` - an attacker-controlled value. Applications using `ctx.hostname` for URL generation, password reset links, email verification URLs, or routing decisions are vulnerable to Host header injection attacks. Versions 3.1.2 and 2.16.4 fix the issue.

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Puntuación base: 7.5

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.52%
Percentil entre todas las CVEs puntuadas: 42
Fecha de la puntuación: 6/10/2026

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).

🎯 Técnicas ATT&CK

Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.

ExplotaciónT1190 Exploit Public-Facing Applicationinitial access85 %
Impacto principalT1565.002 Transmitted Data Manipulationimpact75 %
Impacto secundarioT1598.003 Spearphishing Linkreconnaissance70 %

Host header injection en aplicación web expuesta (AV:N, PR:N): ctx.hostname vulnerable permite manipular URLs de reset y verificación (I:H). Impactos: manipulación de datos (enlaces maliciosos inyectados) y phishing (credenciales vía enlaces falsos).

Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.

🛡️ Mitigaciones ATT&CK que cubren estas técnicas

Vulnerability Scanning User Training Privileged Account Management Network Segmentation Limit Access to Resource Over Network Filter Network Traffic

Tecnologías afectadas (1)

Koajs — KOA

CWE

CWE-20
NVD-CWE-noinfo
CWE-20

Referencias

JSON original (NVD)

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      "value": "Koa is middleware for Node.js using ES2017 async functions. Prior to versions 3.1.2 and 2.16.4, Koa's `ctx.hostname` API performs naive parsing of the HTTP Host header, extracting everything before the first colon without validating the input conforms to RFC 3986 hostname syntax. When a malformed Host header containing a `@` symbol is received, `ctx.hostname` returns `evil[.]com` - an attacker-controlled value. Applications using `ctx.hostname` for URL generation, password reset links, email verification URLs, or routing decisions are vulnerable to Host header injection attacks. Versions 3.1.2 and 2.16.4 fix the issue."
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      "value": "Koa es un middleware para Node.js que utiliza funciones asíncronas de ES2017. Antes de las versiones 3.1.2 y 2.16.4, la API `ctx.hostname` de Koa realiza un análisis ingenuo del encabezado Host HTTP, extrayendo todo lo que precede al primer signo de dos puntos sin validar que la entrada cumpla con la sintaxis de nombre de host de RFC 3986. Cuando se recibe un encabezado Host malformado que contiene un símbolo '@', `ctx.hostname` devuelve 'evil[.]com' - un valor controlado por el atacante. Las aplicaciones que utilizan `ctx.hostname` para la generación de URL, enlaces de restablecimiento de contraseña, URL de verificación de correo electrónico o decisiones de enrutamiento son vulnerables a ataques de inyección de encabezado Host. Las versiones 3.1.2 y 2.16.4 solucionan el problema."
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