"The png_handle_tRNS function in pngrutil.c in libpng before 1.0.25 and 1.2.x
before 1.2.17 allows remote attackers to cause a denial of service (application
crash) via a grayscale PNG image with a bad tRNS chunk CRC value."
libpng10-1.0.26-1.fc6 has been released for Fedora Extras 6, which should
resolve this problem.
There is also a release libpng10-1.0.26-1.fc7.1 in Fedora 7 updates and
libpng10-1.0.26-1.fc8 for development.