OpenSSH / dropbearSSHd xauth command injection

* OpenSSH * affects all version <= 7.2p1 with `X11Forwarding yes` (acc. to OpenSSH this bug is 20 years old and affects all versions back to openssh v1) * status: fixed, vendor advisory: http://www.openssh.com/txt/x11fwd.adv * dropbearSSHd * affects <= 2015.71 (basically all versions that come with x11 support; dates back 12 years [1]) * status: fixed, vendor info: https://matt.ucc.asn.au/dropbear/CHANGES * other * mobaSSH; they're just based on openssh but for windows - mobassh.mobatek.net allows to bypass ssh-forced-commands and login-shell restrictions (/bin/false, specific binary) by injecting xauth commands. The latter only affects OpenSSH. Capabilities: arbitr. file read/write, info disclosure (xauth env. info), initiate outbound X connections reported to OpenSSH first, provided detailed vulnerability analysis, PoC and a simple patch. OpenSSH kindly coordinated patch and release with dropbearSSHd. fixed within a few days (first contact march 3rd. coordinated release with dropbear 10th) details and the actual research material that was securely disclosed to OpenSSH will be pushed to the following repo (note this llink is subject to change once there's a cve assigned for that issue): https://github.com/tintinweb/pub/tree/master/pocs/cve-2016-xxxx-openssh-dropbearsshd [1] https://github.com/mkj/dropbear/blob/790726519e69f5d93b579a21951d78f8f777a5cb/svr-x11fwd.c