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I have an admin panel that is running off a mysql db. On that panel, I have text boxes that allow an "Admin" to input plain text OR HTML Styling that will be displayed on a section of the site that is live. So for example, A user might input the following in a Title textbox;

<b>The 'Rory' jumped over the moon</b>

The text boxes are set to only allow specific html syntax.

Does that prevent a web shell from being dropped on to the web server through the text boxes?

  • Is there a way to bypass the filtering?
  • If you manipulated the data in the DB, would it allow php to run?
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closed as not a real question by Rook, Iszi, Gilles, Terry Chia, this.josh Oct 26 '12 at 5:58

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not enough information. –  Rook Oct 25 '12 at 14:49

1 Answer 1

It is very unlikely that this would be a viable route to dropping a web shell. The input is probably stored in a database, not in a file, so the interpreter (ASP, PHP, etc) will not process it as source code. A much more likely attack vector is Cross Site Scripting, if the filter is not strict enough.

EDIT to answer 2 points added later:

  • There is no way to know if the filter can be bypassed without analyzing the source or attempting to bypass it.
  • Understand how the PHP interpreter is invoked by the web server. In most cases, the web server calls the appropriate interpreter based on a file's extension (e.g. .php calls the PHP interpreter). The web server does not retrieve content directly from the database, so it cannot invoke the interpreter on database content. A vulnerability would exist if a PHP page retrieved user-defined strings from the database and eval'd them. I hope you can understand how unlikely such a situation would be.

Shortest form of this answer: Probably not, but try it if you don't believe me.

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There is a number of PHP based applications out there which store their configuration in a php file. And provide an admin panel to modify it... –  Hendrik Brummermann Oct 26 '12 at 7:39
    
@HendrikBrummermann just when I thought PHP couldn't get any dumber... –  bonsaiviking Oct 26 '12 at 14:15

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