The png_push_read_zTXt function in pngpread.c in libpng 1.0.x before 1.0.58, 1.2.x before 1.2.48, 1.4.x before 1.4.10, and 1.5.x before 1.5.10 allows remote attackers to cause a denial of service (out-of-bounds read) via a large avail_in field value in a PNG image.
http://www.ubuntu.com/usn/USN-2815-1
http://www.openwall.com/lists/oss-security/2012/07/24/5
http://www.openwall.com/lists/oss-security/2012/07/24/3
http://lists.opensuse.org/opensuse-updates/2012-08/msg00004.html