Se ha lanzado una versi\u00f3n corregida de OpenSSH 9.9p2, en la que se han solucionado dos vulnerabilidades identificadas por Qualys. Se ha demostrado un ejemplo de uso de estas vulnerabilidades para llevar a cabo un ataque MITM, permitiendo redirigir el tr\u00e1fico a un servidor falso al intentar que un cliente se conecte a un servidor SSH, eludiendo la verificaci\u00f3n de las claves del host y creando la ilusi\u00f3n de que el cliente se conecta al servidor deseado (el cliente SSH aceptar\u00e1 la clave del host del servidor falso en lugar de la clave del servidor leg\u00edtimo). <\/p>\n
La primera vulnerabilidad (CVE-2025-26465) se debe a un error l\u00f3gico en la utilidad ssh, que permite eludir la verificaci\u00f3n de la identidad del servidor y llevar a cabo un ataque MITM. El problema se presenta a partir de la versi\u00f3n OpenSSH 6.8p1 (diciembre de 2014) en configuraciones con la opci\u00f3n VerifyHostKeyDNS habilitada. En la instalaci\u00f3n base de OpenSSH, esta opci\u00f3n est\u00e1 desactivada por defecto, pero estuvo habilitada en la configuraci\u00f3n de ssh en FreeBSD hasta marzo de 2023. <\/p>\n
El problema radica en que en el c\u00f3digo de la funci\u00f3n verify_host_key_callback(), al llamar a la funci\u00f3n verify_host_key(), solo se verifica el c\u00f3digo de error «-1», mientras que otros c\u00f3digos, como «-2», son ignorados. Como resultado, la funci\u00f3n verify_host_key_callback() puede devolver un c\u00f3digo exitoso «0», a pesar de que la funci\u00f3n verify_host_key() haya devuelto un error «-2». El c\u00f3digo de error «-2» es devuelto por la funci\u00f3n verify_host_key() cuando hay falta de memoria. Si se crean condiciones que impidan la asignaci\u00f3n de memoria en la funci\u00f3n verify_host_key(), SSH considerar\u00e1 que la clave del host fue verificada con \u00e9xito. Para crear tales condiciones, un servidor SSH falso del atacante, al que se redirige al cliente, devuelve la clave del host del tama\u00f1o m\u00e1ximo posible (256KB), y al mismo tiempo se explota una fuga de memoria en el lado del cliente SSH. <\/p>\n
Las condiciones para crear una fuga de memoria se logran gracias a la segunda vulnerabilidad (CVE-2025-26466), que afecta tanto al cliente ssh como al servidor<\/a> sshd, y explotado sin autenticaci\u00f3n. La vulnerabilidad permite agotar la memoria disponible del proceso y crear una alta carga en la CPU al enviar una gran cantidad de paquetes SSH2_MSG_PING. En el manejador de paquetes SSH2_MSG_PING hay una fuga de memoria que se manifiesta desde la versi\u00f3n OpenSSH 9.5p1 (agosto de 2023). La fuga ocurre porque a cada paquete PING de 16 bytes se le asigna un b\u00fafer de 256 bytes para formar una respuesta, pero este b\u00fafer solo se libera despu\u00e9s de completar la negociaci\u00f3n de claves. Como soluci\u00f3n de protecci\u00f3n, se sugiere configurar restricciones usando las directivas LoginGraceTime, MaxStartups y PerSourcePenalties. \u0414\u043e\u0441\u0442\u0443\u043f\u0435\u043d \u043a\u043e\u0440\u0440\u0435\u043a\u0442\u0438\u0440\u0443\u044e\u0449\u0438\u0439 \u0432\u044b\u043f\u0443\u0441\u043a OpenSSH 9.9p2, \u0432 \u043a\u043e\u0442\u043e\u0440\u043e\u043c \u0443\u0441\u0442\u0440\u0430\u043d\u0435\u043d\u044b \u0434\u0432\u0435 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0438, \u0432\u044b\u044f\u0432\u043b\u0435\u043d\u043d\u044b\u0435 \u043a\u043e\u043c\u043f\u0430\u043d\u0438\u0435\u0439 Qualys. \u041f\u0440\u043e\u0434\u0435\u043c\u043e\u043d\u0441\u0442\u0440\u0438\u0440\u043e\u0432\u0430\u043d \u043f\u0440\u0438\u043c\u0435\u0440 \u0438\u0441\u043f\u043e\u043b\u044c\u0437\u043e\u0432\u0430\u043d\u0438\u044f \u0434\u0430\u043d\u043d\u044b\u0445 \u0443\u044f\u0437\u0432\u0438\u043c\u043e\u0441\u0442\u0435\u0439 \u0434\u043b\u044f \u0441\u043e\u0432\u0435\u0440\u0448\u0435\u043d\u0438\u044f MITM-\u0430\u0442\u0430\u043a\u0438, \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u044e\u0449\u0435\u0439 \u043f\u0440\u0438 \u043f\u043e\u043f\u044b\u0442\u043a\u0435 \u043f\u043e\u0434\u043a\u043b\u044e\u0447\u0435\u043d\u0438\u044f \u043a\u043b\u0438\u0435\u043d\u0442\u0430 \u043a SSH-\u0441\u0435\u0440\u0432\u0435\u0440\u0443, \u043f\u0435\u0440\u0435\u043d\u0430\u043f\u0440\u0430\u0432\u0438\u0442\u044c \u0442\u0440\u0430\u0444\u0438\u043a \u043d\u0430 \u0441\u043e\u0431\u0441\u0442\u0432\u0435\u043d\u043d\u044b\u0439 \u0444\u0438\u043a\u0442\u0438\u0432\u043d\u044b\u0439 \u0441\u0435\u0440\u0432\u0435\u0440, \u043e\u0431\u043e\u0439\u0442\u0438 \u043f\u0440\u043e\u0432\u0435\u0440\u043a\u0443 \u0445\u043e\u0441\u0442\u043e\u0432\u044b\u0445 \u043a\u043b\u044e\u0447\u0435\u0439 \u0438 \u0441\u043e\u0437\u0434\u0430\u0442\u044c \u0443 \u043a\u043b\u0438\u0435\u043d\u0442\u0430 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Fuente: opennet.ru<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"