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383 lines
18 KiB
XML
383 lines
18 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
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<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
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<!-- $LastChangedRevision$ -->
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<!--
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<modulesynopsis metafile="mod_privileges.xml.meta">
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<name>mod_privileges</name>
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<description>Support for Solaris privileges and for running virtual hosts
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under different user IDs.</description>
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<status>Experimental</status>
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<sourcefile>mod_privileges.c</sourcefile>
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<identifier>privileges_module</identifier>
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<compatibility>Available in Apache 2.3 and up, on Solaris 10 and
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OpenSolaris platforms</compatibility>
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<summary>
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<p>This module enables different Virtual Hosts to run with different
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Unix <var>User</var> and <var>Group</var> IDs, and with different
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<a href="http://sosc-dr.sun.com/bigadmin/features/articles/least_privilege.jsp"
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>Solaris Privileges</a>. In particular, it offers a solution to the
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problem of privilege separation between different Virtual Hosts, first
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promised by the abandoned perchild MPM. It also offers other security
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enhancements.</p>
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<p>Unlike perchild, <module>mod_privileges</module>
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is not itself an MPM. It works <em>within</em> a processing model to
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set privileges and User/Group <em>per request</em> in a running process.
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It is therefore not compatible with a threaded MPM, and will refuse
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to run under one.</p>
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<p><module>mod_privileges</module> raises security issues similar to
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those of <a href="../suexec.html">suexec</a>. But unlike suexec,
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it applies not only to CGI programs but to the entire request processing
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cycle, including in-process applications and subprocesses.
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It is ideally suited to running PHP applications under <strong>mod_php</strong>,
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which is also incompatible with threaded MPMs. It is also well-suited
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to other in-process scripting applications such as <strong>mod_perl</strong>,
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<strong>mod_python</strong>, and <strong>mod_ruby</strong>, and to
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applications implemented in C as apache modules where privilege
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separation is an issue.</p>
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</summary>
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<section id="security"><title>Security Considerations</title>
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<p><module>mod_privileges</module> introduces new security concerns
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in situations where <strong>untrusted code</strong> may be run
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<strong>within the webserver process</strong>. This applies to
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untrusted modules, and scripts running under modules such as
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mod_php or mod_perl. Scripts running externally (e.g. as CGI
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or in an appserver behind mod_proxy or mod_jk) are NOT affected.</p>
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<p>The basic security concerns with mod_privileges are:</p>
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<ul><li>Running as a system user introduces the same security issues
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as mod_suexec, and near-equivalents such as cgiwrap and suphp.</li>
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<li>A privileges-aware malicious user extension (module or script)
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could escalate its privileges to anything available to the
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httpd process in any virtual host. This introduces new risks
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if (and only if) mod_privileges is compiled with the
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<var>BIG_SECURITY_HOLE</var> option.</li>
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<li>A privileges-aware malicious user extension (module or script)
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could escalate privileges to set its user ID to another system
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user (and/or group).</li>
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</ul>
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<p>The <directive>PrivilegesMode</directive> directive allows you to
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select either <var>FAST</var> or <var>SECURE</var> mode. You can
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mix modes, using <var>FAST</var> mode for trusted users and
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fully-audited code paths, while imposing SECURE mode where an
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untrusted user has scope to introduce code.</p>
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<p>Before describing the modes, we should also introduce the target
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use cases: Benign vs Hostile. In a benign situation, you want to
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separate users for their convenience, and protect them and the server
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against the risks posed by honest mistakes, but you trust your users
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are not deliberately subverting system security. In a hostile
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situation - e.g. commercial hosting - you may have users deliberately
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attacking the system or each other.</p>
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<dl>
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<dt>FAST mode</dt>
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<dd>In <var>FAST</var> mode, requests are run in-process with the
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selected uid/gid and privileges, so the overhead is negligible.
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This is suitable for benign situations, but is not secure against an
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attacker escalating privileges with an in-process module or script.</dd>
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<dt>SECURE mode</dt>
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<dd>A request in <var>SECURE</var> mode forks a subprocess, which
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then drops privileges. This is a very similar case to running CGI
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with suexec, but for the entire request cycle, and with the benefit
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of fine-grained control of privileges.</dd>
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</dl>
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<p>You can select different <directive>PrivilegesMode</directive>s for
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each virtual host, and even in a directory context within a virtual
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host. <var>FAST</var> mode is appropriate where the user(s) are
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trusted and/or have no privilege to load in-process code.
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<var>SECURE</var> mode is appropriate to cases where untrusted code
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might be run in-process. However, even in <var>SECURE</var> mode,
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there is no protection against a malicious user who is able to
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introduce privileges-aware code running <em>before the start of the
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request-processing cycle.</em></p>
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</section>
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<directivesynopsis>
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<name>PrivilegesMode</name>
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<description>Trade off processing speed and efficiency vs security against
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malicious privileges-aware code.</description>
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<syntax>PrivilegesMode FAST|SECURE|SELECTIVE</syntax>
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<default>PrivilegesMode FAST</default>
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<contextlist>
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<context>server config</context>
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<context>virtual host</context>
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<context>directory</context>
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</contextlist>
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<compatibility>Available on Solaris 10 and OpenSolaris with
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non-threaded MPMs (<module>prefork</module> or custom MPM).</compatibility>
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<usage><p>This directive trades off performance vs security against
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malicious, privileges-aware code. In <var>SECURE</var> mode, each request
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runs in a secure subprocess, incurring a substantial performance penalty.
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In <var>FAST</var> mode, the server is not protected against escalation
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of privileges as discussed above.</p>
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<p>This directive differs slightly between a <code><Directory></code>
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context (including equivalents such as Location/Files/If) and a
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top-level or <code><VirtualHost></code>.</p>
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<p>At top-level, it sets a default that will be inherited by virtualhosts.
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In a virtual host, FAST or SECURE mode acts on the entire
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HTTP request, and any settings in a <code><Directory></code>
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context will be <strong>ignored</strong>. A third pseudo-mode
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SELECTIVE defers the choice of FAST vs SECURE to directives in a
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<code><Directory></code> context.</p>
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<p>In a <code><Directory></code> context, it is applicable only
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where SELECTIVE mode was set for the VirtualHost. Only
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FAST or SECURE can be set in this context (SELECTIVE would be
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meaningless).</p>
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<note type="warning"><title>Warning</title>
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Where SELECTIVE mode is selected for a virtual host, the activation
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of privileges must be deferred until <em>after</em> the mapping
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phase of request processing has determined what
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<code><Directory></code> context applies to the request.
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This might give an attacker opportunities to introduce
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code through a <directive module="mod_rewrite">RewriteMap</directive>
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running at top-level or <code><VirtualHost></code> context
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<em>before</em> privileges have been dropped and userid/gid set.
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</note>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>VHostUser</name>
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<description>Sets the User ID under which a virtual host runs.</description>
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<syntax>VHostUser <var>unix-userid</var></syntax>
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<default>Inherits the userid specified in
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<directive module="mod_unixd">User</directive></default>
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<contextlist><context>virtual host</context></contextlist>
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<compatibility>Available on Solaris 10 and OpenSolaris with
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non-threaded MPMs (<module>prefork</module> or custom MPM).</compatibility>
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<usage>
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<p>The <directive>VHostUser</directive> directive sets the Unix userid
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under which the server will process requests to a virtualhost.
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The userid is set before the request is processed and reset afterwards
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using <a
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href="http://sosc-dr.sun.com/bigadmin/features/articles/least_privilege.jsp"
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>Solaris Privileges</a>. Since the setting applies to the
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<em>process</em>, this is not compatible with threaded MPMs.</p>
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<p><var>Unix-userid</var> is one of:</p>
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<dl>
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<dt>A username</dt>
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<dd>Refers to the given user by name.</dd>
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<dt><code>#</code> followed by a user number.</dt>
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<dd>Refers to a user by its number.</dd>
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</dl>
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<note type="warning"><title>Security</title>
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<p>This directive cannot be used to run apache as root!
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Nevertheless, it opens potential security issues similar to
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those discussed in the <a href="../suexec.html">suexec</a>
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documentation.</p></note>
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</usage>
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<seealso><directive module="mod_unixd">User</directive></seealso>
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<seealso><directive module="mod_suexec">SuexecUserGroup</directive></seealso>
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</directivesynopsis>
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<directivesynopsis>
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<name>VHostGroup</name>
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<description>Sets the Group ID under which a virtual host runs.</description>
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<syntax>VHostGroup <var>unix-groupid</var></syntax>
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<default>Inherits the group id specified in
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<directive module="mod_unixd">Group</directive></default>
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<contextlist><context>virtual host</context></contextlist>
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<compatibility>Available on Solaris 10 and OpenSolaris with
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non-threaded MPMs (<module>prefork</module> or custom MPM).</compatibility>
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<usage>
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<p>The <directive>VHostGroup</directive> directive sets the Unix group
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under which the server will process requests to a virtualhost.
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The group is set before the request is processed and reset afterwards
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using <a
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href="http://sosc-dr.sun.com/bigadmin/features/articles/least_privilege.jsp"
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>Solaris Privileges</a>. Since the setting applies to the
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<em>process</em>, this is not compatible with threaded MPMs.</p>
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<p><var>Unix-group</var> is one of:</p>
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<dl>
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<dt>A group name</dt>
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<dd>Refers to the given group by name.</dd>
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<dt><code>#</code> followed by a group number.</dt>
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<dd>Refers to a group by its number.</dd>
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</dl>
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<note type="warning"><title>Security</title>
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<p>This directive cannot be used to run apache as root!
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Nevertheless, it opens potential security issues similar to
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those discussed in the <a href="../suexec.html">suexec</a>
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documentation.</p></note>
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</usage>
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<seealso><directive module="mod_unixd">Group</directive></seealso>
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<seealso><directive module="mod_suexec">SuexecUserGroup</directive></seealso>
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</directivesynopsis>
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<directivesynopsis>
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<name>VHostSecure</name>
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<description>Determines whether the server runs with enhanced security
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for the virtualhost.</description>
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<syntax>VHostSecure On|Off</syntax>
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<default>VHostSecure On</default>
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<contextlist><context>virtual host</context></contextlist>
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<compatibility>Available on Solaris 10 and OpenSolaris with
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non-threaded MPMs (<module>prefork</module> or custom MPM).</compatibility>
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<usage>
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<p>Determines whether the virtual host processes requests with
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security enhanced by removal of <a
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href="http://sosc-dr.sun.com/bigadmin/features/articles/least_privilege.jsp"
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>Privileges</a> that are rarely needed in a webserver, but which are
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available by default to a normal Unix user and may therefore
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be required by modules and applications. It is recommended that
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you retain the default (On) unless it prevents an application running.
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Since the setting applies to the <em>process</em>, this is not
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compatible with threaded MPMs.</p>
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<note><title>Note</title>
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<p>If <directive>VHostSecure</directive> prevents an application
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running, this may be a warning sign that the application should be
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reviewed for security.</p></note>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>VHostCGIMode</name>
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<description>Determines whether the virtualhost can run
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subprocesses, and the privileges available to subprocesses.</description>
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<syntax>VHostCGIMode On|Off|Secure</syntax>
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<default>VHostCGIMode On</default>
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<contextlist><context>virtual host</context></contextlist>
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<compatibility>Available on Solaris 10 and OpenSolaris with
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non-threaded MPMs (<module>prefork</module> or custom MPM).</compatibility>
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<usage>
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<p>Determines whether the virtual host is allowed to run fork and exec,
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the <a
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href="http://sosc-dr.sun.com/bigadmin/features/articles/least_privilege.jsp"
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>privileges</a> required to run subprocesses. If this is set to
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<var>Off</var> the virtualhost is denied the privileges and will not
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be able to run traditional CGI programs or scripts under the traditional
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<module>mod_cgi</module>, nor similar external programs such as those
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created by <module>mod_ext_filter</module> or
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<directive module="mod_rewrite">RewriteMap</directive> <var>prog</var>.
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Note that it does not prevent CGI programs running under alternative
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process and security models such as <a href="https://httpd.apache.org/mod_fcgid/"
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>mod_fcgid</a>, which is a recommended solution in Solaris.</p>
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<p>If set to <var>On</var> or <var>Secure</var>, the virtual host
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is permitted to run external programs and scripts as above.
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Setting <directive>VHostCGIMode</directive> <var>Secure</var> has
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the effect of denying privileges to the subprocesses, as described
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for <directive>VHostSecure</directive>.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>DTracePrivileges</name>
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<description>Determines whether the privileges required by dtrace are enabled.</description>
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<syntax>DTracePrivileges On|Off</syntax>
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<default>DTracePrivileges Off</default>
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<contextlist><context>server config</context></contextlist>
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<compatibility>Available on Solaris 10 and OpenSolaris with
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non-threaded MPMs (<module>prefork</module> or custom MPM).</compatibility>
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<usage>
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<p>This server-wide directive determines whether Apache will run with
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the <a
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href="http://sosc-dr.sun.com/bigadmin/features/articles/least_privilege.jsp"
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>privileges</a> required to run
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<a href="http://sosc-dr.sun.com/bigadmin/content/dtrace/">dtrace</a>.
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Note that <var>DTracePrivileges On</var> will not in itself
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activate DTrace, but <var>DTracePrivileges Off</var> will prevent
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it working.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>VHostPrivs</name>
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<description>Assign arbitrary privileges to a virtual host.</description>
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<syntax>VHostPrivs [+-]?<var>privilege-name</var> [[+-]?privilege-name] ...</syntax>
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<default>None</default>
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<contextlist><context>virtual host</context></contextlist>
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<compatibility>Available on Solaris 10 and OpenSolaris with
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non-threaded MPMs (<module>prefork</module> or custom MPM)
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and when <module>mod_privileges</module> is compiled with the
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<var>BIG_SECURITY_HOLE</var> compile-time option.</compatibility>
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<usage>
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<p><directive>VHostPrivs</directive> can be used to assign arbitrary <a
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href="http://sosc-dr.sun.com/bigadmin/features/articles/least_privilege.jsp"
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>privileges</a> to a virtual host. Each <var>privilege-name</var>
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is the name of a Solaris privilege, such as <var>file_setid</var>
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or <var>sys_nfs</var>.</p>
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<p>A <var>privilege-name</var> may optionally be prefixed by
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+ or -, which will respectively allow or deny a privilege.
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If used with neither + nor -, all privileges otherwise assigned
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to the virtualhost will be denied. You can use this to override
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any of the default sets and construct your own privilege set.</p>
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<note type="warning"><title>Security</title>
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<p>This directive can open huge security holes in apache, up to
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and including running requests with root-level powers. Do not
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use it unless you fully understand what you are doing!</p></note>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>VHostCGIPrivs</name>
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<description>Assign arbitrary privileges to subprocesses created
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by a virtual host.</description>
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<syntax>VHostPrivs [+-]?<var>privilege-name</var> [[+-]?privilege-name] ...</syntax>
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<default>None</default>
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<contextlist><context>virtual host</context></contextlist>
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<compatibility>Available on Solaris 10 and OpenSolaris with
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non-threaded MPMs (<module>prefork</module> or custom MPM)
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and when <module>mod_privileges</module> is compiled with the
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<var>BIG_SECURITY_HOLE</var> compile-time option.</compatibility>
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<usage>
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<p><directive>VHostCGIPrivs</directive> can be used to assign arbitrary <a
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href="http://sosc-dr.sun.com/bigadmin/features/articles/least_privilege.jsp"
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>privileges</a> to subprocesses created by a virtual host, as discussed
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under <directive>VHostCGIMode</directive>. Each <var>privilege-name</var>
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is the name of a Solaris privilege, such as <var>file_setid</var>
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or <var>sys_nfs</var>.</p>
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<p>A <var>privilege-name</var> may optionally be prefixed by
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+ or -, which will respectively allow or deny a privilege.
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If used with neither + nor -, all privileges otherwise assigned
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to the virtualhost will be denied. You can use this to override
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any of the default sets and construct your own privilege set.</p>
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<note type="warning"><title>Security</title>
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<p>This directive can open huge security holes in apache subprocesses,
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up to and including running them with root-level powers. Do not
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use it unless you fully understand what you are doing!</p></note>
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</usage>
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</directivesynopsis>
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</modulesynopsis>
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