CVE-2016-0702

La función MOD_EXP_CTIME_COPY_FROM_PREBUF en crypto/bn/bn_exp.c en OpenSSL 1.0.1 en versiones anteriores a 1.0.1s y 1.0.2 en versiones anteriores a 1.0.2g no considera correctamente las veces que se accede al cache-bank durante la exponenciación modular, lo que facilita a usuarios locales descubrir las claves RSA ejecutando una aplicación manipulada en el mismo núcleo de la CPU Intel Sandy Bridge como víctima y aprovechándose de los conflictos del cache-bank, también conocida como un ataque "CacheBleed".

A side-channel attack was found that makes use of cache-bank conflicts on the Intel Sandy-Bridge microarchitecture. An attacker who has the ability to control code in a thread running on the same hyper-threaded core as the victim's thread that is performing decryption, could use this flaw to recover RSA private keys.

An update that contains security fixes can now be installed. This update for openssl fixes various security issues. OpenSSL was vulnerable to a cross-protocol attack that could lead to decryption of TLS sessions by using a server supporting SSLv2 and EXPORT cipher suites as a Bleichenbacher RSA padding oracle. This update changes the openssl library to. Disable SSLv2 protocol support by default. This can be overridden by setting the environment variable "OPENSSL_ALLOW_SSL2" or by using SSL_CTX_clear_options using the SSL_OP_NO_SSLv2 flag. Note that various services and clients had already disabled SSL protocol 2 by default previously. Disable all weak EXPORT ciphers by default. These can be reenabled if required by old legacy software using the environment variable "OPENSSL_ALLOW_EXPORT".