pngrtran.c in libpng 1.5.x before 1.5.1 allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via a crafted palette-based PNG image that triggers a buffer overflow, related to the png_do_expand_palette function, the png_do_rgb_to_gray function, and an integer underflow. NOTE: some of these details are obtained from third party information.
https://exchange.xforce.ibmcloud.com/vulnerabilities/64637
http://www.vupen.com/english/advisories/2011/0080
http://www.kb.cert.org/vuls/id/643140
http://securitytracker.com/id?1024955