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Bug #47796 preg_replace /e modifier allows unexpected code execution
Submitted: 2009-03-26 22:36 UTC Modified: 2009-03-26 22:45 UTC
From: spam04 at pornel dot net Assigned:
Status: Not a bug Package: PCRE related
PHP Version: 5.2.9 OS: *
Private report: No CVE-ID: None
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Bug Type:
From: spam04 at pornel dot net
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 [2009-03-26 22:36 UTC] spam04 at pornel dot net
preg_replace does not escape $ character. If double quotes are used in 
replacement code, this enables unwanted injection of variables or even 
execution of PHP code.

My suggestion is to escape $ character and discourage use of single 
quotes in replacement code (because they're not compatible with the way 
$ and " are escaped).

Reproduce code:
// simple case:
preg_replace('/.*/e','strtoupper("$0")', '$foo');

// code execution:
class test
    function pwnd() {echo "pwnd!\n";}
    function replace($str)
        preg_replace('/.*/e','strtoupper("$0")', $str);

$t = new test();

Expected result:

Actual result:
PHP Notice:  Undefined variable: foo


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 [2009-03-26 22:38 UTC] spam04 at pornel dot net
I forgot to add echo before preg_replace() in reproduce code.
 [2009-03-26 22:45 UTC]
Sorry, but your problem does not imply a bug in PHP itself.  For a
list of more appropriate places to ask for help using PHP, please
visit as this bug system is not the
appropriate forum for asking support questions.  Due to the volume
of reports we can not explain in detail here why your report is not
a bug.  The support channels will be able to provide an explanation
for you.

Thank you for your interest in PHP.

Use preg_replace_callback instead.
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