The publickey_from_privatekey function in libssh before 0.5.4, when no algorithm is matched during negotiations, allows remote attackers to cause a denial of service (NULL pointer dereference and crash) via a "Client: Diffie-Hellman Key Exchange Init" packet.
http://lists.fedoraproject.org/pipermail/package-announce/2013-February/098065.html
http://lists.fedoraproject.org/pipermail/package-announce/2013-February/098094.html
http://secunia.com/advisories/51982