Hey folks,

I'm in a position now where I'd like to provide access to a binary on a web-server via a cgi script. I've been handed a cgi that does the job reasonably well, but I'm not convinced it's at all secure or robust, so I'd like some confirmation/advice on it.

The first problem is it wasn't written using CGI.pm and I'm not quite up to re-writing it the right way just now unless I absolutely have to. Here's what it does:

  1. Checks for the presence of the binary in an accessible location. (It used to be looking for it in /usr/local/bin! I've changed that.)
  2. It expects to be called as the GET action from a form, so it checks to make sure it got a single parameter from the form. (Since this parameter is a standard regular expression, I can't realistically filter out too much from the input stream.)
  3. Open an anonymous pipe for input like so:
    4. unless (open(PIPE, "search \"$pattern\" |")) {
     # barf out some error messages
}
# carry on processing the output from the search command

    [download]

Now is it just me, or is this opening a sub-shell and thus providing a way for almost anyone to execute almost any code on my web-server with (at least) the permissions of the server's UID/GID? Is there a way I can insist that the open() command execute a restricted shell, or better yet only execute the 'search' command without a shell at all so I don't have to worry about evil escape sequences that I can't really quotemeta since they are regexps?

Thanks,

-J.

In reply to Question about input pipes and sub-shells by Joey The Saint

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