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.

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".