Security and Safe Mode
|safe_mode||"0"||PHP_INI_SYSTEM||Removed in PHP 5.4.0.|
|safe_mode_gid||"0"||PHP_INI_SYSTEM||Removed in PHP 5.4.0.|
|safe_mode_include_dir||NULL||PHP_INI_SYSTEM||Removed in PHP 5.4.0.|
|safe_mode_exec_dir||""||PHP_INI_SYSTEM||Removed in PHP 5.4.0.|
|safe_mode_allowed_env_vars||"PHP_"||PHP_INI_SYSTEM||Removed in PHP 5.4.0.|
|safe_mode_protected_env_vars||"LD_LIBRARY_PATH"||PHP_INI_SYSTEM||Removed in PHP 5.4.0.|
Here's a short explanation of the configuration directives.
By default, Safe Mode does a UID compare check when opening files. If you want to relax this to a GID compare, then turn on safe_mode_gid. Whether to use UID (
FALSE) or GID (
TRUE) checking upon file access.
UID/GID checks are bypassed when including files from this directory and its subdirectories (directory must also be in include_path or full path must including).This directive can take a colon (semi-colon on Windows) separated path in a fashion similar to the include_path directive, rather than just a single directory. The restriction specified is actually a prefix, not a directory name. This means that "safe_mode_include_dir = /dir/incl" also allows access to "/dir/include" and "/dir/incls" if they exist. When you want to restrict access to only the specified directory, end with a slash. For example: "safe_mode_include_dir = /dir/incl/" If the value of this directive is empty, no files with different UID/GID can be included.
If PHP is used in safe mode, system() and the other functions executing system programs refuse to start programs that are not in this directory. You have to use / as directory separator on all environments including Windows.
Setting certain environment variables may be a potential security breach. This directive contains a comma-delimited list of prefixes. In Safe Mode, the user may only alter environment variables whose names begin with the prefixes supplied here. By default, users will only be able to set environment variables that begin with PHP_ (e.g. PHP_FOO=BAR).
This directive contains a comma-delimited list of environment variables that the end user won't be able to change using putenv(). These variables will be protected even if safe_mode_allowed_env_vars is set to allow to change them.
-rw-rw-r-- 1 rasmus rasmus 33 Jul 1 19:20 script.php -rw-r--r-- 1 root root 1116 May 26 18:01 /etc/passwd
<?php readfile('/etc/passwd'); ?>
results in this error when safe mode is enabled:
Warning: SAFE MODE Restriction in effect. The script whose uid is 500 is not allowed to access /etc/passwd owned by uid 0 in /docroot/script.php on line 2
However, there may be environments where a strict UID check is not appropriate and a relaxed GID check is sufficient. This is supported by means of the safe_mode_gid switch. Setting it to On performs the relaxed GID checking, setting it to Off (the default) performs UID checking.
<Directory /docroot> php_admin_value open_basedir /docroot </Directory>
If you run the same script.php with this open_basedir setting then this is the result:
Warning: open_basedir restriction in effect. File is in wrong directory in /docroot/script.php on line 2
You can also disable individual functions. Note that the disable_functions directive can not be used outside of the php.ini file which means that you cannot disable functions on a per-virtualhost or per-directory basis in your httpd.conf file. If we add this to our php.ini file:
disable_functions = readfile,system
Then we get this output:
Warning: readfile() has been disabled for security reasons in /docroot/script.php on line 2
These PHP restrictions are not valid in executed binaries, of course.