Multiple heap-based buffer overflows in the modpow function in PuTTY before 0.55 allow (1) remote attackers to execute arbitrary code via an SSH2 packet with a base argument that is larger than the mod argument, which causes the modpow function to write memory before the beginning of its buffer, and (2) remote malicious servers to cause a denial of service (client crash) and possibly execute arbitrary code via a large bignum during authentication.
marc.info/?l=bugtraq&m=109167869528138&w=2
secunia.com/advisories/12212/
www.chiark.greenend.org.uk/~sgtatham/putty/changes.html
www.chiark.greenend.org.uk/~sgtatham/putty/wishlist/vuln-modpow.html
www.gentoo.org/security/en/glsa/glsa-200408-04.xml
www.securityfocus.com/bid/10850
exchange.xforce.ibmcloud.com/vulnerabilities/16885