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[2010-10-13 14:10 UTC] php dot net at site dot lanzz dot org
Description:
------------
The documentation states that "[allow_url_fopen] can only be set in php.ini due
to security reasons". This is a completely wrong approach, as it also prevents
security-conscious developers to DISABLE the dangerous allow_url_fopen option,
if it is enabled server-wide (for example in a shared hosting setup).
Having a single point of control over allow_url_fopen forces the entire
webserver and all websites and applications to share the same setting, which in
some cases would force administrators to enable the option due to poorly written
third-party code which might be unfeasible to fix or replace, which would lower
security for other code that relies on allow_url_fopen being off, and it's not
possible to selectively disable it where it really is not needed.
The added security of restricting allow_url_fopen to php.ini only is
questionable, as malicious users can use other means to access remote URLs,
while legitimate users are left without the option of controlled access to
remote URLs.
The best scenario would be a globally disabled allow_url_fopen option (which
really should be the default), with the possibility for controlled enabling of
the feature only where its needed.
Test script:
---------------
# php.ini
allow_url_fopen = On
# test.php
ini_set('allow_url_fopen', 0);
print(ini_get('allow_url_fopen')? 'enabled', 'disabled');
Expected result:
----------------
disabled
Actual result:
--------------
enabled
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Last updated: Tue Apr 01 19:01:31 2025 UTC |
The url wrappers are an unfortunate feature that should have never been implemented the way it is. Still, there is existing code out there that relies on it, so neither reimplementing it better nor disabling it globally via allow_url_fopen seem like good options. Why not rely on the php_admin_flag mechanism for restricting allow_url_fopen? It will make it possible for administrators to disable it globally without letting end-users to re-enable it (for example in a shared hosting context), or let administrators leave it unrestricted and manage it at runtime (for example in a dedicated server). I find it useful to be able to turn on url fopen in a controlled manner, like so: ini_set('allow_url_fopen', 1); $content = file_get_contents('http://remote/resource'); ini_set('allow_url_fopen', 0); This approach will not be possible if only tightening is allowed, as this code will run correctly only once per script execution. Using php_admin_flag this code either will work as expected (turning allow_url_fopen on and off and accessing the resource), or will not work at all, which will be much easier to catch in development.