Quoting security updates section of the upstream page:
All current OptiPNG versions are known to be vulnerable to memory
reallocation attacks, due to a bug in the GIF image reader. (Many
thanks to Roy Tam for the report, as well as the fix.)
Upstream patch to be included in future upstream versions:
Created attachment 333177 [details]
Local copy of the upstream patch
optipng-0.6.2.1-1.fc10 has been submitted as an update for Fedora 10.
optipng-0.6.2.1-1.fc9 has been submitted as an update for Fedora 9.
optipng-0.6.2.1-1.fc9 has been pushed to the Fedora 9 stable repository. If problems still persist, please make note of it in this bug report.
optipng-0.6.2.1-1.fc10 has been pushed to the Fedora 10 stable repository. If problems still persist, please make note of it in this bug report.
Use-after-free vulnerability in the GIFReadNextExtension function in
lib/pngxtern/gif/gifread.c in OptiPNG 0.6.2 and earlier allows
context-dependent attackers to cause a denial of service (application
crash) via a crafted GIF image that causes the realloc function to
return a new pointer, which triggers memory corruption when the old
pointer is accessed.