mirror of
https://github.com/sigmasternchen/php-doc-en
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af4410a7e1
still using this, after discussion on the phpdoc list. From now on, manual.ced will need to be found at ~/.phpdoc/manual.ced. git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@288721 c90b9560-bf6c-de11-be94-00142212c4b1
245 lines
10 KiB
XML
245 lines
10 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision$ -->
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<!-- splitted from ./index.xml, last change in rev 1.66 -->
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<chapter xml:id="security.cgi-bin" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>Installed as CGI binary</title>
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<sect1 xml:id="security.cgi-bin.attacks">
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<title>Possible attacks</title>
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<simpara>
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Using PHP as a <acronym>CGI</acronym> binary is an option for
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setups that for some reason do not wish to integrate PHP as a
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module into server software (like Apache), or will use PHP with
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different kinds of <acronym>CGI</acronym> wrappers to create safe chroot and setuid
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environments for scripts. This setup usually involves installing
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executable PHP binary to the web server cgi-bin directory. CERT
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advisory <link xlink:href="&url.cert;">CA-96.11</link> recommends
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against placing any interpreters into cgi-bin. Even if the PHP
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binary can be used as a standalone interpreter, PHP is designed
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to prevent the attacks this setup makes possible:
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</simpara>
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<itemizedlist>
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<listitem>
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<simpara>
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Accessing system files: <filename
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role="url">http://my.host/cgi-bin/php?/etc/passwd</filename>
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</simpara>
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<simpara>
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The query information in a URL after the question mark (?) is
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passed as command line arguments to the interpreter by the CGI
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interface. Usually interpreters open and execute the file
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specified as the first argument on the command line.
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</simpara>
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<simpara>
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When invoked as a CGI binary, PHP refuses to interpret the
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command line arguments.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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Accessing any web document on server: <filename
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role="url">http://my.host/cgi-bin/php/secret/doc.html</filename>
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</simpara>
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<simpara>
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The path information part of the URL after the PHP binary name,
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<filename role="uri">/secret/doc.html</filename> is
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conventionally used to specify the name of the file to be
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opened and interpreted by the <acronym>CGI</acronym> program.
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Usually some web server configuration directives (Apache:
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Action) are used to redirect requests to documents like
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<filename
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role="url">http://my.host/secret/script.php</filename> to the
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PHP interpreter. With this setup, the web server first checks
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the access permissions to the directory <filename
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role="uri">/secret</filename>, and after that creates the
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redirected request <filename
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role="url">http://my.host/cgi-bin/php/secret/script.php</filename>.
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Unfortunately, if the request is originally given in this form,
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no access checks are made by web server for file <filename
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role="uri">/secret/script.php</filename>, but only for the
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<filename role="uri">/cgi-bin/php</filename> file. This way
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any user able to access <filename
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role="uri">/cgi-bin/php</filename> is able to access any
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protected document on the web server.
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</simpara>
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<simpara>
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In PHP, compile-time configuration option <link
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linkend="configure.enable-force-cgi-redirect">--enable-force-cgi-redirect</link>
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and runtime configuration directives <link
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linkend="ini.doc-root">doc_root</link> and <link
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linkend="ini.user-dir">user_dir</link> can be used to prevent
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this attack, if the server document tree has any directories
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with access restrictions. See below for full the explanation
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of the different combinations.
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</simpara>
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</listitem>
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</itemizedlist>
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</sect1>
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<sect1 xml:id="security.cgi-bin.default">
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<title>Case 1: only public files served</title>
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<simpara>
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If your server does not have any content that is not restricted
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by password or ip based access control, there is no need for
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these configuration options. If your web server does not allow
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you to do redirects, or the server does not have a way to
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communicate to the PHP binary that the request is a safely
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redirected request, you can specify the option <link
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linkend="configure.enable-force-cgi-redirect">--enable-force-cgi-redirect</link>
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to the configure script. You still have to make sure your PHP
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scripts do not rely on one or another way of calling the script,
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neither by directly <filename
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role="php">http://my.host/cgi-bin/php/dir/script.php</filename>
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nor by redirection <filename
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role="php">http://my.host/dir/script.php</filename>.
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</simpara>
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<simpara>
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Redirection can be configured in Apache by using AddHandler and
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Action directives (see below).
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</simpara>
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</sect1>
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<sect1 xml:id="security.cgi-bin.force-redirect">
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<title>Case 2: using <literal>--enable-force-cgi-redirect</literal></title>
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<simpara>
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This compile-time option prevents anyone from calling PHP
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directly with a URL like <filename
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role="php">http://my.host/cgi-bin/php/secretdir/script.php</filename>.
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Instead, PHP will only parse in this mode if it has gone through
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a web server redirect rule.
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</simpara>
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<simpara>
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Usually the redirection in the Apache configuration is done with
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the following directives:
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</simpara>
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<programlisting role="apache-conf">
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<![CDATA[
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Action php-script /cgi-bin/php
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AddHandler php-script .php
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]]>
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</programlisting>
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<simpara>
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This option has only been tested with the Apache web server, and
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relies on Apache to set the non-standard CGI environment variable
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<envar>REDIRECT_STATUS</envar> on redirected requests. If your
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web server does not support any way of telling if the request is
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direct or redirected, you cannot use this option and you must use
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one of the other ways of running the CGI version documented
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here.
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</simpara>
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</sect1>
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<sect1 xml:id="security.cgi-bin.doc-root">
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<title>Case 3: setting doc_root or user_dir</title>
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<simpara>
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To include active content, like scripts and executables, in the
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web server document directories is sometimes considered an insecure
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practice. If, because of some configuration mistake, the scripts
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are not executed but displayed as regular HTML documents, this
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may result in leakage of intellectual property or security
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information like passwords. Therefore many sysadmins will prefer
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setting up another directory structure for scripts that are
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accessible only through the PHP CGI, and therefore always
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interpreted and not displayed as such.
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</simpara>
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<simpara>
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Also if the method for making sure the requests are not
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redirected, as described in the previous section, is not
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available, it is necessary to set up a script doc_root that is
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different from web document root.
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</simpara>
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<simpara>
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You can set the PHP script document root by the configuration
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directive <link linkend="ini.doc-root">doc_root</link> in the
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<link linkend="configuration.file">configuration file</link>, or
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you can set the environment variable
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<envar>PHP_DOCUMENT_ROOT</envar>. If it is set, the <acronym>CGI</acronym>
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version of PHP will always construct the file name to open with this
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<parameter>doc_root</parameter> and the path information in the
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request, so you can be sure no script is executed outside this
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directory (except for <parameter>user_dir</parameter>
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below).
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</simpara>
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<simpara>
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Another option usable here is <link
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linkend="ini.user-dir">user_dir</link>. When user_dir is unset,
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only thing controlling the opened file name is
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<parameter>doc_root</parameter>. Opening a URL like <filename
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role="url">http://my.host/~user/doc.php</filename> does not
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result in opening a file under users home directory, but a file
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called <filename role="uri">~user/doc.php</filename> under
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doc_root (yes, a directory name starting with a tilde
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[<literal>~</literal>]).
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</simpara>
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<simpara>
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If user_dir is set to for example <filename
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role="dir">public_php</filename>, a request like <filename
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role="url">http://my.host/~user/doc.php</filename> will open a
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file called <filename>doc.php</filename> under the directory
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named <filename role="dir">public_php</filename> under the home
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directory of the user. If the home of the user is <filename
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role="dir">/home/user</filename>, the file executed is
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<filename>/home/user/public_php/doc.php</filename>.
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</simpara>
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<simpara>
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<parameter>user_dir</parameter> expansion happens regardless of
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the <parameter>doc_root</parameter> setting, so you can control
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the document root and user directory access
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separately.
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</simpara>
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</sect1>
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<sect1 xml:id="security.cgi-bin.shell">
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<title>Case 4: PHP parser outside of web tree</title>
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<para>
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A very secure option is to put the PHP parser binary somewhere
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outside of the web tree of files. In <filename
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role="dir">/usr/local/bin</filename>, for example. The only real
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downside to this option is that you will now have to put a line
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similar to:
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<informalexample>
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<programlisting>
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<![CDATA[
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#!/usr/local/bin/php
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]]>
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</programlisting>
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</informalexample>
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as the first line of any file containing PHP tags. You will also
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need to make the file executable. That is, treat it exactly as
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you would treat any other CGI script written in Perl or sh or any
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other common scripting language which uses the
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<literal>#!</literal> shell-escape mechanism for launching
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itself.
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</para>
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<para>
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To get PHP to handle <envar>PATH_INFO</envar> and
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<envar>PATH_TRANSLATED</envar> information correctly with this
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setup, the PHP parser should be compiled with the <link
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linkend="configure.enable-discard-path">--enable-discard-path</link>
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configure option.
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</para>
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</sect1>
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</chapter>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-omittag:t
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sgml-shorttag:t
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"~/.phpdoc/manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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