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securityvulnsSecurityvulnsSECURITYVULNS:DOC:16289
HistoryMar 09, 2007 - 12:00 a.m.

[Full-disclosure] PHP import_request_variables() vs extract()

2007-03-0900:00:00
vulners.com
13

Please note that also extract() will override any variable exluded
$GLOBALS but the main difference is that on http://it2.php.net/extract
you are advised to do not use "extract() against untrusted data, like
user-input ($_GET, …)."

[quote]
if you want to run old code that relies on register_globals temporarily,
make sure you use one of the non-overwriting extract_type values such
as EXTR_SKIP and be aware that you should extract in the same order
that's defined in variables_order within the php.ini
[/quote]

Infact extract() has a EXTR_SKIP flag that implement this bhreaviuw:

[quote]
If there is a collision, don't overwrite the existing variable.
[/quote]

Using extract() with EXTR_SKIP will give you something like GLOBALS ON
that is safe if compared with what happens using extract($_GET); or
import_request_variables('G');

— >8 — >8 — >8 — >8 — test1.php — >8 — >8 — >8 — >8

<?php
extract($_GET);
print_r($_SERVER);
?>

— >8 — >8 — >8 — >8 — --------- — >8 — >8 — >8 — >8

Demo: test1.php?SERVER=abc
Expected result: the _SERVER array will became a string

The morale is that while an insecure usage of extract() by a developer
could be his fault there is no secure usage of
import_request_variables() and this is surely a PHP fault.

Regards,
Francesco 'ascii' Ongaro
http://www.ush.it/


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