libssh2 - security update

Mariusz Ziulek reported that libssh2, a SSH2 client-side library, was
reading and using the SSH_MSG_KEXINIT packet without doing sufficient
range checks when negotiating a new SSH session with a remote server. A
malicious attacker could man in the middle a real server and cause a
client using the libssh2 library to crash (denial of service) or
otherwise read and use unintended memory areas in this process.

For Debian 6 Squeeze, these issues have been fixed in libssh2 version 1.2.6-1+deb6u1