CVE-2015-3197

ssl/s2_srvr.c en OpenSSL 1.0.1 en versiones anteriores a 1.0.1r y 1.0.2 en versiones anteriores a 1.0.2f no impide el uso de cifrados deshabilitados, lo que hace que sea más fácil para atacantes man-in-the-middle vencer los mecanismos de protección criptográfica llevando a cabo cálculos sobre tráfico SSLv2, relacionado con las funciones get_client_master_key y get_client_hello.

A flaw was found in the way malicious SSLv2 clients could negotiate SSLv2 ciphers that were disabled on the server. This could result in weak SSLv2 ciphers being used for SSLv2 connections, making them vulnerable to man-in-the-middle attacks.

Historically OpenSSL usually only ever generated DH parameters based on "safe" primes. More recently (in version 1.0.2) support was provided for generating X9.42 style parameter files such as those required for RFC 5114 support. The primes used in such files may not be "safe". Where an application is using DH configured with parameters based on primes that are not "safe" then an attacker could use this fact to find a peer's private DH exponent. This attack requires that the attacker complete multiple handshakes in which the peer uses the same private DH exponent. For example this could be used to discover a TLS server's private DH exponent if it's reusing the private DH exponent or it's using a static DH ciphersuite. Other issues were also addressed.