The vulnerability is caused due to the incorrect use of libpng within the function "gdPngReadData()" in ext/gd/libgd/gd_png.c of the GD extension when processing truncated data. This can be exploited to cause an infinite loop by e.g. tricking an application to process a specially crafted file. (reported by Xavier Roche)

This issue has been confirmed in PHP versions 4.4.7 and 5.2.2 but may affect others. The issue has already been corrected, however, and can be fetched from the PHP CVS system to protect your system.