Imager::File::PNG versions from 1.003 before 1.004 for Perl write past the end of the row buffer reading a PNG with a tRNS transparency chunk in readdirect8.

With a tRNS chunk, readdirect8() adds an alpha channel to the image it creates but still sizes the row buffer from the original channel count. libpng expands the transparency into that extra channel, so pngreadrow() fills one channel more than the buffer holds, at one byte per sample, and writes width bytes past the end of the allocation. Palette images go to readpaletted() and 16-bit images to readdirect16(), which sizes its buffer from pnggetrowbytes() and allocates enough for the expanded row.

The same reader ships bundled in the Imager distribution.

Reading an attacker-supplied PNG through Imager->read() corrupts the heap, which can crash the process.