Integer overflow in PuTTY 0.62 and earlier, WinSCP before 5.1.6, and other products that use PuTTY allows remote SSH servers to cause a denial of service (crash) and possibly execute arbitrary code in certain applications that use PuTTY via a negative size value in an RSA key signature during the SSH handshake, which triggers a heap-based buffer overflow.
http://www.search-lab.hu/advisories/secadv-20130722
http://www.debian.org/security/2013/dsa-2736
http://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/vuln-signature-stringlen.html
http://winscp.net/tracker/show_bug.cgi?id=1017
http://svn.tartarus.org/sgt?view=revision&sortby=date&revision=9896
http://secunia.com/advisories/54533
http://secunia.com/advisories/54517
http://secunia.com/advisories/54379
http://lists.opensuse.org/opensuse-updates/2013-08/msg00041.html
http://lists.opensuse.org/opensuse-updates/2013-08/msg00035.html