PDF::WebKit versions through 1.2 for Perl allow OS command injection via a 2-arg open() of the output path in to_pdf and of stylesheet paths in _style_tag_for.
to_pdf reads the generated PDF back from its path argument, and _style_tag_for reads each entry of the stylesheets list, by assigning the path to a local @ARGV and reading it with the diamond operator, which opens each @ARGV element with Perl's 2-arg open(). A value that begins or ends with a pipe ("| cmd", "cmd |") is run as a command rather than opened as a file, and one that begins with a redirect ("> path", ">> path") opens that path for write or append. to_file forwards its path argument to to_pdf and reaches the same read.
Any caller that forwards untrusted input as the output path or as a stylesheets entry can run a command under the process UID; with the "cmd |" form the command's output is returned in place of the PDF, and with the "> path" form the named file is truncated. Stylesheets may only be added to an HTML source, so a URL or file source exposes the output path alone.
No fixed release is available. Apply the patch, which reads both paths with a 3-arg open so the value is never interpreted as a command or redirect.
Otherwise, do not pass untrusted input as the output path to to_pdf or to_file, or as an entry in the stylesheets list.
Note that the wkhtmltopdf project is no longer being developed, and users of this package should migrate to alternative solutions.