Neat! Your parser [1] almost has a similar issue because a comm could contain parenthesis, e.g., `foo) R 123 456`. But since a comm is limited to 64 bytes, I don't think it is possible to fit a fully matching string inside of the comm before the closing parent after the comm, which would thus make your regexp fail to match.
I just had a quick read of the pid/stat parser, and the regex pattern starts with ^, but there's no $. Doesn't this mean that this parser suffers exactly the bug of the original post?
Right, it's not a security problem on its own, but it can make the regex not match at all causing jc to return an error. So jc suffers from the parsing bug mentioned in the post.
[edit:] In order to get jc to return an error one has to actually read the regex. Here is a file name that gets it to return an error:
Edit: looks like I can tighten up the signature matching regex for the "magic" syntax per the issue found above. The greedy regex matching for the parser does seem to work fine, though.
[1] https://github.com/kellyjonbrazil/jc/blob/master/jc/parsers/...