Perhaps I don't understand the parent node as it was intended, but if I do correctly grok it, I think it's misleading, at best.

Oversimplifying a bit, when the -T CLI option is on, anything that comes from outside the script is "tainted."

Untainting data (be it ENV, $vars or anything else) can be fairly easy... but often is anything but 'easy' or simple. Consider, for example, data received as input from a form on a website.

However, take a simple case, where login_data (an ID and yeah, this is old) was supposed to be five digits -- no more, no less, and nothing that's not an (arabic) digit. Since the user entry is tainted, the cgi in use untaints the login_data (to the site owner's satisfaction) by checking that the id received consists of exactly five digits:

unless ( $value =~ /^\d{5}$/ )          # UNTAINT
   {
   out_badlog();
   warn ("bad after UNTAINT\n");
   exit;
   }

[download]

Ascertaining that the five digits comprise a valid ID is a different topic and is performed in another part of the script.

So, moving on to this from perlsec:

"SECURITY MECHANISMS AND CONCERNS
Taint mode
Perl automatically enables a set of special security checks, called *taint mode*, when it detects its program running with differing real and effective user or group IDs. The setuid bit in Unix permissions is mode 04000, the setgid bit mode 02000; either or both may be set. You can also enable taint mode explicitly by using the -T command line flag. This flag is *strongly* suggested for server programs and any program run on behalf of someone else, such as a CGI script."

perlsec offers much more of relevance to the immediately previous comment from kennethk.

There's more in perlfaq7.pod about determining "if a variable (emphasis supplied) is tainted" ...after which pf7 offers these gems:

" You can use the tainted() function of the Scalar::Util module, ....See also 'Laundering and Detecting Tainted Data' in perlsec."

Frankly, I (for just one, I hope) was unaware (because of far too cursory reading of its docs) that S:C offered capabilities there. I hope this belated epiphany is useful to others.

Updated: Para 1 added and paras 2,3 and 4 edited for clarity


++$anecdote ne $data


In reply to Re^3: Taint and Shellshock by ww
in thread Taint and Shellshock by kennethk

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