The researchers Cyril Arnaud and Pierre-Alain Fouque
investigated the PolarSSL RSA implementation and discovered
a bias in the implementation of the Montgomery multiplication
that we used. For which they then show that it can be used to
mount an attack on the RSA key. Although their test attack is
done on a local system, there seems to be enough indication
that this can properly be performed from a remote system as
well.
All versions prior to PolarSSL 1.2.9 and 1.3.0 are affected
if a third party can send arbitrary handshake messages to your
server.
If correctly executed, this attack reveals the entire private
RSA key after a large number of attack messages (> 600.000 on
a local machine) are sent to show the timing differences.