A security vulnerability in SSL 3.0 has been uncovered
by Bodo Möller and two other Google employees that attackers can exploit to calculate the plaintext of secure connections.
SSL 3.0 is an old protocol and most Internet servers use the newer TLS 1.0, TLS 1.1 or TLS 1.2 protocols instead. Client and server usually agree to use the latest protocol version during connections during protocol handshake but since TLS is backwards compatible with SSL 3.0, it can happen that SSL 3.0 is being used instead.
During the first handshake attempt the highest supported protocol version is offered but if this handshake fails, earlier protocol versions are offered instead.
An attacker controlling the network between the client and server could interfere with the handshake attempt so that SSL 3.0 is used instead of TLS.
