libssh: man-in-the-middle

libssh versions 0.1 and above have a bits/bytes confusion bug and
generate the an anormaly short ephemeral secret for the
diffie-hellman-group1 and diffie-hellman-group14 key exchange methods.
The resulting secret is 128 bits long, instead of the recommended sizes
of 1024 and 2048 bits respectively. There are practical algorithms (Baby
steps/Giant steps, Pollard’s rho) that can solve this problem in O(2^63)
operations.

Both client and server are are vulnerable, pre-authentication. This
vulnerability could be exploited by an eavesdropper with enough
resources to decrypt or intercept SSH sessions. The bug was found during
an internal code review by Aris Adamantiadis of the libssh team.