CVE-2015-1794

La función ssl3_get_key_exchange en ssl/s3_clnt.c en OpenSSL 1.0.2 en versiones anteriores a 1.0.2e permite a servidores remotos provocar una denegación de servicio (fallo de segmentación) a través de un valor cero p en un mensaje anónimo de Diffie-Hellman (DH) ServerKeyExchange.

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.