CVE-2015-3193

La implementación de exponenciación al cuadrado de Montgomery en crypto/bn/asm/x86_64-mont5.pl en OpenSSL 1.0.2 en versiones anteriores a 1.0.2e en la plataforma x86_64, como se utiliza por la función BN_mod_exp, no maneja correctamente la propagación de acarreo y produce una salida incorrecta, lo que hace más fácil para atacantes remotos obtener información sensible de las claves privadas a través de un ataque contra el uso de una suite de cifrado (1) Diffie-Hellman (DH) o (2) Diffie-Hellman Ephemeral (DHE).

There is a carry propagating bug in the x86_64 Montgomery squaring procedure. No EC algorithms are affected. Analysis suggests that attacks against RSA and DSA as a result of this defect would be very difficult to perform and are not believed likely. Attacks against DH are considered just feasible (although very difficult) because most of the work necessary to deduce information about a private key may be performed offline. The amount of resources required for such an attack would be very significant and likely only accessible to a limited number of attackers. An attacker would additionally need online access to an unpatched system using the target private key in a scenario with persistent DH parameters and a private key that is shared between multiple clients. For example this can occur by default in OpenSSL DHE based SSL/TLS ciphersuites. Other issues were also addressed.