Microsoft Windows Schannel Security Feature Bypass Vulnerability

A security feature bypass vulnerability exists in Secure Channel (Schannel) that is caused by an issue in the TLS state machine whereby a client system accepts an RSA key with a shorter key length than the originally negotiated key length. The vulnerability facilitates exploitation of the publicly disclosed FREAK technique, which is an industry-wide issue that is not specific to Windows operating systems.

In a man-in-the-middle (MiTM) attack, an attacker could downgrade the key length of an RSA key to EXPORT-grade length in an encrypted TLS session. The attacker could then intercept and decrypt this traffic. Any Windows system connecting to a TLS server as a client is affected. An attacker who successfully exploited this vulnerability could perform MiTM attacks that could decrypt encrypted traffic.