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://bugs.debian.org/cgi-bin/bugreport.cgi?bug=718779
http://lists.opensuse.org/opensuse-updates/2013-08/msg00035.html
http://lists.opensuse.org/opensuse-updates/2013-08/msg00041.html
http://secunia.com/advisories/54379
http://secunia.com/advisories/54517
http://secunia.com/advisories/54533
http://www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/vuln-signature-stringlen.html