Javascript debugger
Website design
↑
Table of Contents
The PHP safe mode is an attempt to solve the shared-server security problem. It is architecturally incorrect to try to solve this problem at the PHP level, but since the alternatives at the web server and OS levels aren't very realistic, many people, especially ISP's, use safe mode for now.
Safe Mode was removed in PHP 6.0.0.
Name | Default | Changeable | Changelog |
---|---|---|---|
safe_mode | "0" | PHP_INI_SYSTEM | Removed in PHP 6.0.0. |
safe_mode_gid | "0" | PHP_INI_SYSTEM | Available since PHP 4.1.0. Removed in PHP 6.0.0. |
safe_mode_include_dir | NULL | PHP_INI_SYSTEM | Available since PHP 4.1.0. Removed in PHP 6.0.0. |
safe_mode_exec_dir | "" | PHP_INI_SYSTEM | Removed in PHP 6.0.0. |
safe_mode_allowed_env_vars | "PHP_" | PHP_INI_SYSTEM | Removed in PHP 6.0.0. |
safe_mode_protected_env_vars | "LD_LIBRARY_PATH" | PHP_INI_SYSTEM | Removed in PHP 6.0.0. |
open_basedir | NULL | PHP_INI_ALL | PHP_INI_SYSTEM in PHP < 6. |
disable_functions | "" | php.ini only | Available since PHP 4.0.1. |
disable_classes | "" | php.ini only | Available since PHP 4.3.2. |
For further details and definition of the PHP_INI_* constants see
ini_set().
Here's a short explanation of the configuration directives.
Whether to enable PHP's safe mode.
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).
As of PHP 4.2.0, 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 in
PHP 4.2.3 and as of PHP 4.3.3. In earlier versions, all files could 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).
If this directive is empty, PHP will let the user modify ANY environment variable!
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.
Limit the files that can be opened by PHP to the specified directory-tree, including the file itself. This directive is NOT affected by whether Safe Mode is turned On or Off.
When a script tries to open a file with, for example, fopen() or gzopen(), the location of the file is checked. When the file is outside the specified directory-tree, PHP will refuse to open it. All symbolic links are resolved, so it's not possible to avoid this restriction with a symlink. If the file doesn't exist then the symlink couldn't be resolved and the filename is compared to (a resolved) open_basedir.
The special value .
indicates that the working directory of the script will be used as the
base-directory. This is, however, a little dangerous as the working directory
of the script can easily be changed with chdir().
In httpd.conf
, open_basedir can be turned off
(e.g. for some virtual hosts)
the same way as
any other configuration directive with "php_admin_value open_basedir
none".
Under Windows, separate the directories with a semicolon. On all other systems, separate the directories with a colon. As an Apache module, open_basedir paths from parent directories are now automatically inherited.
The restriction specified with open_basedir is actually a prefix, not a directory name. This means that "open_basedir = /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: "open_basedir = /dir/incl/"
Support for multiple directories was added in 3.0.7.
The default is to allow all files to be opened.
This directive allows you to disable certain functions for security reasons. It takes on a comma-delimited list of function names. disable_functions is not affected by Safe Mode.
This directive must be set in php.ini
For example, you
cannot set this in httpd.conf
.
This directive allows you to disable certain classes for security reasons. It takes on a comma-delimited list of class names. disable_classes is not affected by Safe Mode.
This directive must be set in php.ini
For example, you
cannot set this in httpd.conf
.
This directive became available in PHP 4.3.2
See also: register_globals, display_errors, and log_errors.
When safe_mode is on, PHP checks to see if the owner of the current script matches the owner of the file to be operated on by a file function or its directory. For example:
-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
Running script.php:
<?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.
If instead of safe_mode, you set an
open_basedir directory then all
file operations will be limited to files under the specified directory.
For example (Apache httpd.conf
example):
<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.