The ssh_agent_channel_data function in PuTTY before 0.68 allows remote attackers to have unspecified impact via a large length value in an agent protocol message and leveraging the ability to connect to the Unix-domain socket representing the forwarded agent connection, which trigger a buffer overflow.
https://www.exploit-db.com/exploits/42137/
https://security.gentoo.org/glsa/201706-09
https://security.gentoo.org/glsa/201703-03
http://www.securitytracker.com/id/1038067
http://www.securityfocus.com/bid/97156
http://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/vuln-agent-fwd-overflow.html
http://lists.opensuse.org/opensuse-updates/2017-03/msg00055.html