<!--# set var="title" value="PHP/PERL/Ruby exploit" -->
<!--# set var="date" value="February 9, 2006" -->

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Take the __PHP__ code:

	<?php
	$filename = ‘content/’.$_REQUEST[’filename’].’.html’;
	include($filename);
	?>

This is exploitable in an obvious way; “../” can be included in the filename, and it can be used to open any file ending in “.html” that’s readable by the web user. However, there’s a second, less obvious exploit path.

If magic\_quotes\_gpc is off, the following is possible:

	test.php?filename=../../../../../../etc/passwd%00

PHP stores strings internally as binary-safe, but the include() requires a syscall, which expects a nil-terminated string. The result is that the syscall considers the string over at the \0, and opens /etc/passwd. PHP should really check to see if the binary-safe string contains nils before the syscall, and fail with an error if it does.

---

In __PERL__:

	open IN,”foo\0bar”;

causes the syscall:

	open(”foo”, O_RDONLY|O_LARGEFILE)

---

In __Ruby__:

	File.open(”foo\0bar”,’r');

causes the syscall:

	open(”foo”, O_RDONLY|O_LARGEFILE)

---

__Python__ appears to be safe:

	open(”foo\0bar”,”r”);

throws an error:

	TypeError: file() argument 1 must be (encoded string without NULL bytes), not str

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