GD versions before 2.86 for Perl allow OS command injection and file overwrite via a 2-arg open() of filename arguments in _make_filehandle.
GD::Image::_make_filehandle opens a filename argument with Perl's 2-arg open(), so a filename that begins or ends with a pipe ("| cmd", "cmd |") or begins with a redirect ("> path", ">> path") is run as a command or redirect rather than opened as a file. _make_filehandle is the single open path behind every filename-accepting constructor (new, newFromPng, newFromJpeg, and the rest); the in-memory *Data variants do not open a path and are unaffected.
Any caller that forwards untrusted input to one of these constructors as a pathname can run an arbitrary command or truncate a file under the process UID.
For deployments that cannot upgrade to 2.86, do not pass untrusted input as a pathname to GD::Image constructors. Callers can open the file themselves and pass the resulting filehandle, which bypasses the affected string path.
Upgrade to GD 2.86 or later, which opens filename arguments with a 3-arg read open so the filename is never interpreted as a command or redirect.