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-<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
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- XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
- This file is generated from xml source: DO NOT EDIT
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- -->
-<title>Security Tips - Apache HTTP Server</title>
-<link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
-<link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
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-<body id="manual-page"><div id="page-header">
-<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
-<p class="apache">Apache HTTP Server Version 2.0</p>
-<img alt="" src="../images/feather.gif" /></div>
-<div class="up"><a href="./"><img title="&lt;-" alt="&lt;-" src="../images/left.gif" /></a></div>
-<div id="path">
-<a href="http://www.apache.org/">Apache</a> &gt; <a href="http://httpd.apache.org/">HTTP Server</a> &gt; <a href="http://httpd.apache.org/docs/">Documentation</a> &gt; <a href="../">Version 2.0</a> &gt; <a href="./">Miscellaneous Documentation</a></div><div id="page-content"><div id="preamble"><h1>Security Tips</h1>
-<div class="toplang">
-<p><span>Available Languages: </span><a href="../en/misc/security_tips.html" title="English">&nbsp;en&nbsp;</a> |
-<a href="../ko/misc/security_tips.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
-<a href="../tr/misc/security_tips.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
-</div>
-
- <p>Some hints and tips on security issues in setting up a web server.
- Some of the suggestions will be general, others specific to Apache.</p>
- </div>
-<div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#uptodate">Keep up to Date</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#serverroot">Permissions on ServerRoot Directories</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#ssi">Server Side Includes</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#cgi">CGI in General</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#nsaliasedcgi">Non Script Aliased CGI</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#saliasedcgi">Script Aliased CGI</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#dynamic">Other sources of dynamic content</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#systemsettings">Protecting System Settings</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#protectserverfiles">Protect Server Files by Default</a></li>
-<li><img alt="" src="../images/down.gif" /> <a href="#watchyourlogs">Watching Your Logs</a></li>
-</ul></div>
-<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="uptodate" id="uptodate">Keep up to Date</a></h2>
-
- <p>The Apache HTTP Server has a good record for security and a
- developer community highly concerned about security issues. But
- it is inevitable that some problems -- small or large -- will be
- discovered in software after it is released. For this reason, it
- is crucial to keep aware of updates to the software. If you have
- obtained your version of the HTTP Server directly from Apache, we
- highly recommend you subscribe to the <a href="http://httpd.apache.org/lists.html#http-announce">Apache
- HTTP Server Announcements List</a> where you can keep informed of
- new releases and security updates. Similar services are available
- from most third-party distributors of Apache software.</p>
-
- <p>Of course, most times that a web server is compromised, it is
- not because of problems in the HTTP Server code. Rather, it comes
- from problems in add-on code, CGI scripts, or the underlying
- Operating System. You must therefore stay aware of problems and
- updates with all the software on your system.</p>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="serverroot" id="serverroot">Permissions on ServerRoot Directories</a></h2>
-
-
-
- <p>In typical operation, Apache is started by the root user, and it
- switches to the user defined by the <code class="directive"><a href="../mod/mpm_common.html#user">User</a></code> directive to serve hits. As is the
- case with any command that root executes, you must take care that it is
- protected from modification by non-root users. Not only must the files
- themselves be writeable only by root, but so must the directories, and
- parents of all directories. For example, if you choose to place
- ServerRoot in <code>/usr/local/apache</code> then it is suggested that
- you create that directory as root, with commands like these:</p>
-
- <div class="example"><p><code>
- mkdir /usr/local/apache <br />
- cd /usr/local/apache <br />
- mkdir bin conf logs <br />
- chown 0 . bin conf logs <br />
- chgrp 0 . bin conf logs <br />
- chmod 755 . bin conf logs
- </code></p></div>
-
- <p>It is assumed that <code>/</code>, <code>/usr</code>, and
- <code>/usr/local</code> are only modifiable by root. When you install the
- <code class="program"><a href="../programs/httpd.html">httpd</a></code> executable, you should ensure that it is
- similarly protected:</p>
-
- <div class="example"><p><code>
- cp httpd /usr/local/apache/bin <br />
- chown 0 /usr/local/apache/bin/httpd <br />
- chgrp 0 /usr/local/apache/bin/httpd <br />
- chmod 511 /usr/local/apache/bin/httpd
- </code></p></div>
-
- <p>You can create an htdocs subdirectory which is modifiable by other
- users -- since root never executes any files out of there, and shouldn't
- be creating files in there.</p>
-
- <p>If you allow non-root users to modify any files that root either
- executes or writes on then you open your system to root compromises.
- For example, someone could replace the <code class="program"><a href="../programs/httpd.html">httpd</a></code> binary so
- that the next time you start it, it will execute some arbitrary code. If
- the logs directory is writeable (by a non-root user), someone could replace
- a log file with a symlink to some other system file, and then root
- might overwrite that file with arbitrary data. If the log files
- themselves are writeable (by a non-root user), then someone may be
- able to overwrite the log itself with bogus data.</p>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="ssi" id="ssi">Server Side Includes</a></h2>
-
-
-
- <p>Server Side Includes (SSI) present a server administrator with
- several potential security risks.</p>
-
- <p>The first risk is the increased load on the server. All
- SSI-enabled files have to be parsed by Apache, whether or not
- there are any SSI directives included within the files. While this
- load increase is minor, in a shared server environment it can become
- significant.</p>
-
- <p>SSI files also pose the same risks that are associated with CGI
- scripts in general. Using the <code>exec cmd</code> element, SSI-enabled
- files can execute any CGI script or program under the permissions of the
- user and group Apache runs as, as configured in
- <code>httpd.conf</code>.</p>
-
- <p>There are ways to enhance the security of SSI files while still
- taking advantage of the benefits they provide.</p>
-
- <p>To isolate the damage a wayward SSI file can cause, a server
- administrator can enable <a href="../suexec.html">suexec</a> as
- described in the <a href="#cgi">CGI in General</a> section.</p>
-
- <p>Enabling SSI for files with <code>.html</code> or <code>.htm</code>
- extensions can be dangerous. This is especially true in a shared, or high
- traffic, server environment. SSI-enabled files should have a separate
- extension, such as the conventional <code>.shtml</code>. This helps keep
- server load at a minimum and allows for easier management of risk.</p>
-
- <p>Another solution is to disable the ability to run scripts and
- programs from SSI pages. To do this replace <code>Includes</code>
- with <code>IncludesNOEXEC</code> in the <code class="directive"><a href="../mod/core.html#options">Options</a></code> directive. Note that users may
- still use <code>&lt;--#include virtual="..." --&gt;</code> to execute CGI
- scripts if these scripts are in directories designated by a <code class="directive"><a href="../mod/mod_alias.html#scriptalias">ScriptAlias</a></code> directive.</p>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="cgi" id="cgi">CGI in General</a></h2>
-
-
-
- <p>First of all, you always have to remember that you must trust the
- writers of the CGI scripts/programs or your ability to spot potential
- security holes in CGI, whether they were deliberate or accidental. CGI
- scripts can run essentially arbitrary commands on your system with the
- permissions of the web server user and can therefore be extremely
- dangerous if they are not carefully checked.</p>
-
- <p>All the CGI scripts will run as the same user, so they have potential
- to conflict (accidentally or deliberately) with other scripts e.g. User
- A hates User B, so he writes a script to trash User B's CGI database. One
- program which can be used to allow scripts to run as different users is
- <a href="../suexec.html">suEXEC</a> which is included with Apache as of
- 1.2 and is called from special hooks in the Apache server code. Another
- popular way of doing this is with
- <a href="http://cgiwrap.unixtools.org/">CGIWrap</a>.</p>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="nsaliasedcgi" id="nsaliasedcgi">Non Script Aliased CGI</a></h2>
-
-
-
- <p>Allowing users to execute CGI scripts in any directory should only be
- considered if:</p>
-
- <ul>
- <li>You trust your users not to write scripts which will deliberately
- or accidentally expose your system to an attack.</li>
- <li>You consider security at your site to be so feeble in other areas,
- as to make one more potential hole irrelevant.</li>
- <li>You have no users, and nobody ever visits your server.</li>
- </ul>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="saliasedcgi" id="saliasedcgi">Script Aliased CGI</a></h2>
-
-
-
- <p>Limiting CGI to special directories gives the admin control over what
- goes into those directories. This is inevitably more secure than non
- script aliased CGI, but only if users with write access to the
- directories are trusted or the admin is willing to test each
- new CGI script/program for potential security holes.</p>
-
- <p>Most sites choose this option over the non script aliased CGI
- approach.</p>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="dynamic" id="dynamic">Other sources of dynamic content</a></h2>
-
-
-
- <p>Embedded scripting options which run as part of the server itself,
- such as <code>mod_php</code>, <code>mod_perl</code>, <code>mod_tcl</code>,
- and <code>mod_python</code>, run under the identity of the server itself
- (see the <code class="directive"><a href="../mod/mpm_common.html#user">User</a></code> directive), and
- therefore scripts executed by these engines potentially can access
- anything the server user can. Some scripting engines may provide
- restrictions, but it is better to be safe and assume not.</p>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="systemsettings" id="systemsettings">Protecting System Settings</a></h2>
-
-
-
- <p>To run a really tight ship, you'll want to stop users from setting
- up <code>.htaccess</code> files which can override security features
- you've configured. Here's one way to do it.</p>
-
- <p>In the server configuration file, put</p>
-
- <div class="example"><p><code>
- &lt;Directory /&gt; <br />
- AllowOverride None <br />
- &lt;/Directory&gt;
- </code></p></div>
-
- <p>This prevents the use of <code>.htaccess</code> files in all
- directories apart from those specifically enabled.</p>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="protectserverfiles" id="protectserverfiles">Protect Server Files by Default</a></h2>
-
-
-
- <p>One aspect of Apache which is occasionally misunderstood is the
- feature of default access. That is, unless you take steps to change it,
- if the server can find its way to a file through normal URL mapping
- rules, it can serve it to clients.</p>
-
- <p>For instance, consider the following example:</p>
-
- <div class="example"><p><code>
- # cd /; ln -s / public_html <br />
- Accessing <code>http://localhost/~root/</code>
- </code></p></div>
-
- <p>This would allow clients to walk through the entire filesystem. To
- work around this, add the following block to your server's
- configuration:</p>
-
- <div class="example"><p><code>
- &lt;Directory /&gt; <br />
- Order Deny,Allow <br />
- Deny from all <br />
- &lt;/Directory&gt;
- </code></p></div>
-
- <p>This will forbid default access to filesystem locations. Add
- appropriate <code class="directive"><a href="../mod/core.html#directory">Directory</a></code> blocks to
- allow access only in those areas you wish. For example,</p>
-
- <div class="example"><p><code>
- &lt;Directory /usr/users/*/public_html&gt; <br />
- Order Deny,Allow <br />
- Allow from all <br />
- &lt;/Directory&gt; <br />
- &lt;Directory /usr/local/httpd&gt; <br />
- Order Deny,Allow <br />
- Allow from all <br />
- &lt;/Directory&gt;
- </code></p></div>
-
- <p>Pay particular attention to the interactions of <code class="directive"><a href="../mod/core.html#location">Location</a></code> and <code class="directive"><a href="../mod/core.html#directory">Directory</a></code> directives; for instance, even
- if <code>&lt;Directory /&gt;</code> denies access, a <code>
- &lt;Location /&gt;</code> directive might overturn it.</p>
-
- <p>Also be wary of playing games with the <code class="directive"><a href="../mod/mod_userdir.html#userdir">UserDir</a></code> directive; setting it to
- something like <code>./</code> would have the same effect, for root, as
- the first example above. If you are using Apache 1.3 or above, we strongly
- recommend that you include the following line in your server
- configuration files:</p>
-
- <div class="example"><p><code>
- UserDir disabled root
- </code></p></div>
-
- </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<div class="section">
-<h2><a name="watchyourlogs" id="watchyourlogs">Watching Your Logs</a></h2>
-
-
-
- <p>To keep up-to-date with what is actually going on against your server
- you have to check the <a href="../logs.html">Log Files</a>. Even though
- the log files only reports what has already happened, they will give you
- some understanding of what attacks is thrown against the server and
- allow you to check if the necessary level of security is present.</p>
-
- <p>A couple of examples:</p>
-
- <div class="example"><p><code>
- grep -c "/jsp/source.jsp?/jsp/ /jsp/source.jsp??" access_log <br />
- grep "client denied" error_log | tail -n 10
- </code></p></div>
-
- <p>The first example will list the number of attacks trying to exploit the
- <a href="http://online.securityfocus.com/bid/4876/info/">Apache Tomcat
- Source.JSP Malformed Request Information Disclosure Vulnerability</a>,
- the second example will list the ten last denied clients, for example:</p>
-
- <div class="example"><p><code>
- [Thu Jul 11 17:18:39 2002] [error] [client foo.bar.com] client denied
- by server configuration: /usr/local/apache/htdocs/.htpasswd
- </code></p></div>
-
- <p>As you can see, the log files only report what already has happened, so
- if the client had been able to access the <code>.htpasswd</code> file you
- would have seen something similar to:</p>
-
- <div class="example"><p><code>
- foo.bar.com - - [12/Jul/2002:01:59:13 +0200] "GET /.htpasswd HTTP/1.1"
- </code></p></div>
-
- <p>in your <a href="../logs.html#accesslog">Access Log</a>. This means
- you probably commented out the following in your server configuration
- file:</p>
-
- <div class="example"><p><code>
- &lt;Files ~ "^\.ht"&gt; <br />
- Order allow,deny <br />
- Deny from all <br />
- &lt;/Files&gt;
- </code></p></div>
-
- </div></div>
-<div class="bottomlang">
-<p><span>Available Languages: </span><a href="../en/misc/security_tips.html" title="English">&nbsp;en&nbsp;</a> |
-<a href="../ko/misc/security_tips.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a> |
-<a href="../tr/misc/security_tips.html" hreflang="tr" rel="alternate" title="Türkçe">&nbsp;tr&nbsp;</a></p>
-</div><div id="footer">
-<p class="apache">Copyright 2009 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
-<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>
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