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Sec Bug #55856 preg_replace should fail on trailing garbage
Submitted: 2011-10-06 05:03 UTC Modified: 2014-02-20 22:23 UTC
From: reg dot php at alf dot nu Assigned: yohgaki
Status: Closed Package: PCRE related
PHP Version: 5.4.0beta1 OS: All
Private report: No CVE-ID:
 [2011-10-06 05:03 UTC] reg dot php at alf dot nu
The following (ill-advised but not uncommon) code...

   preg_replace('/'.$a.'/i', $b, $c)

will eval $b if $a contains "/e\0".

Good fix: turn null bytes into backslash-zero before passing them to PCRE.

Easier fix: check that 'pp' is actually at the end of the string and not just at 
some random null byte after the modifier loop in pcre_get_compiled_regex_cache, 
and error out if not.

Test script:
 $word = "die('Lalala'); 1||1/e\0";

// Slightly contrived example, but let's pretend we're
// case-normalizing a user-provided word, and forgot to
// preg_quote

$text = preg_replace('/'.$word.'/i', $word, $text);

Expected result:
"preg_replace(): Unknown modifier '\0' in ..."

(or some better error message)

Actual result:
Code execution.


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 [2011-10-06 05:10 UTC] reg dot php at alf dot nu
Uploading a patch failed (probably because I can't see the task)

 [2014-02-20 22:23 UTC]
-Status: Open +Status: Closed -Assigned To: +Assigned To: yohgaki
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Last updated: Sun Apr 20 01:02:05 2014 UTC