Beefy Boxes and Bandwidth Generously Provided by pair Networks
Do you know where your variables are?
 
PerlMonks  

Comment on

( #3333=superdoc: print w/ replies, xml ) Need Help??

Your code will call anything with whitespace an unsafe string. While that's much better than no checking, how about:

$string =~ s/!([\w\s]+)//; ##add other allowed chars as needed
That will sanitize all strings to contain only numbers, digits, the underscore and whitespace. A more complete regex (which would still not include unicode or international chars) would be:
$string =~ s/!([\w\s\!\@\#\$\%\^\&\*\(\)\\\`\~\-\+\=\,\.]+)//;
(Yes, there's more escaping there than strictly necessary.) Suddenly, that transliteration is looking a lot easier to maintain. If your allowed set is "everything but nulls and control chars", then you're better off explicitly excluding the known control-char set.

Denying all, then allowing is a good general rule of thumb. But, in this case, the "dangerous" items are a fixed set while the "safe" items are much more variable -- so it makes sense to simply remove that which is dangerous.

Update=> Aristotle reminded me that, as \s includes \n, these regexes will not strip newlines; that means strings sanitized with these will be unsafe if executed with a shell (e.g. system("$string");). This further shows that inclusion-matching isn't as good, in this case, as merely stripping "bad" data out.

Anima Legato
.oO all things connect through the motion of the mind


In reply to Re^2: Security techniques every programmer should know by legato
in thread Security techniques every programmer should know by Juerd

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • Outside of code tags, you may need to use entities for some characters:
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.
  • Log In?
    Username:
    Password:

    What's my password?
    Create A New User
    Chatterbox?
    and the web crawler heard nothing...

    How do I use this? | Other CB clients
    Other Users?
    Others rifling through the Monastery: (11)
    As of 2014-12-18 10:59 GMT
    Sections?
    Information?
    Find Nodes?
    Leftovers?
      Voting Booth?

      Is guessing a good strategy for surviving in the IT business?





      Results (50 votes), past polls