(MS15-055) Vulnerability in Schannel Could Allow Information Disclosure (3061518)

This security update addresses a vulnerability in Microsoft Windows, which could allow information disclosure when Secure Channel (Schannel) allows the use of a weak Diffie-Hellman ephemeral (DFE) key length of 512 bits in an encrypted TLS session. Allowing 512-bit DHE keys makes DHE key exchanges weak and vulnerable to various attacks. A server needs to support 512-bit DHE key lengths for an attack to be successful; the minimum allowable DHE key length in default configurations of Windows servers is 1024 bits.