CVE-2014-1295 (Apple's Secure Transport and Triple Handshake Attack) Apple is releasing some updates today. They have not published the bulletins yet, but they are available here: https://gist.github.com/FredericJacobs/11189734.

In the writeup for CVE-2014-1295:


Security - Secure Transport
...

Impact: An attacker with a privileged network position may capture
data or change the operations performed in sessions protected by SSL

Description: In a 'triple handshake' attack, it was possible for an
attacker to establish two connections which had the same encryption
keys and handshake, insert the attacker's data in one connection, and
renegotiate so that the connections may be forwarded to each other.
To prevent attacks based on this scenario, Secure Transport was
changed so that, by default, a renegotiation must present the same
server certificate as was presented in the original connection.



How is it possible to run two instances of a protocol and get the same parameters? Wouldn't nonces specifically neutralize this attack?

(And sorry about the crummy tagging).
The attacker acts as a man-in-the-middle and can forward the clients nonce to the server and the servers nonce to the client. As a result both parties establish a connection with the attacker using the same nonces. 

Because of a weakness in the TLS protocol, the two connections can have the same key, and this key is known to the attacker.

After resumption TLS 'forgets' that the connections were established with the attacker, and did not prevent renegotiation, e.g. using client authentication, between two honest participants. This is corrected by the patch that requires a renegotiation to present the same server certificate as was presented in the original connection.