1 <?xml version="1.0" encoding="ISO-8859-1"?>
2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
3 <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"><head><!--
4 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
5 This file is generated from xml source: DO NOT EDIT
6 XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
8 <title>Security Tips - Apache HTTP Server</title>
9 <link href="../style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" />
10 <link href="../style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" />
11 <link href="../style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" />
12 <link href="../images/favicon.ico" rel="shortcut icon" /></head>
13 <body id="manual-page"><div id="page-header">
14 <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>
15 <p class="apache">Apache HTTP Server Version 2.0</p>
16 <img alt="" src="../images/feather.gif" /></div>
17 <div class="up"><a href="./"><img title="<-" alt="<-" src="../images/left.gif" /></a></div>
19 <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">Miscellaneous Documentation</a></div><div id="page-content"><div id="preamble"><h1>Security Tips</h1>
21 <p><span>Available Languages: </span><a href="../en/misc/security_tips.html" title="English"> en </a> |
22 <a href="../ko/misc/security_tips.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> |
23 <a href="../tr/misc/security_tips.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p>
26 <p>Some hints and tips on security issues in setting up a web server.
27 Some of the suggestions will be general, others specific to Apache.</p>
29 <div id="quickview"><ul id="toc"><li><img alt="" src="../images/down.gif" /> <a href="#uptodate">Keep up to Date</a></li>
30 <li><img alt="" src="../images/down.gif" /> <a href="#serverroot">Permissions on ServerRoot Directories</a></li>
31 <li><img alt="" src="../images/down.gif" /> <a href="#ssi">Server Side Includes</a></li>
32 <li><img alt="" src="../images/down.gif" /> <a href="#cgi">CGI in General</a></li>
33 <li><img alt="" src="../images/down.gif" /> <a href="#nsaliasedcgi">Non Script Aliased CGI</a></li>
34 <li><img alt="" src="../images/down.gif" /> <a href="#saliasedcgi">Script Aliased CGI</a></li>
35 <li><img alt="" src="../images/down.gif" /> <a href="#dynamic">Other sources of dynamic content</a></li>
36 <li><img alt="" src="../images/down.gif" /> <a href="#systemsettings">Protecting System Settings</a></li>
37 <li><img alt="" src="../images/down.gif" /> <a href="#protectserverfiles">Protect Server Files by Default</a></li>
38 <li><img alt="" src="../images/down.gif" /> <a href="#watchyourlogs">Watching Your Logs</a></li>
40 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
42 <h2><a name="uptodate" id="uptodate">Keep up to Date</a></h2>
44 <p>The Apache HTTP Server has a good record for security and a
45 developer community highly concerned about security issues. But
46 it is inevitable that some problems -- small or large -- will be
47 discovered in software after it is released. For this reason, it
48 is crucial to keep aware of updates to the software. If you have
49 obtained your version of the HTTP Server directly from Apache, we
50 highly recommend you subscribe to the <a href="http://httpd.apache.org/lists.html#http-announce">Apache
51 HTTP Server Announcements List</a> where you can keep informed of
52 new releases and security updates. Similar services are available
53 from most third-party distributors of Apache software.</p>
55 <p>Of course, most times that a web server is compromised, it is
56 not because of problems in the HTTP Server code. Rather, it comes
57 from problems in add-on code, CGI scripts, or the underlying
58 Operating System. You must therefore stay aware of problems and
59 updates with all the software on your system.</p>
61 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
63 <h2><a name="serverroot" id="serverroot">Permissions on ServerRoot Directories</a></h2>
67 <p>In typical operation, Apache is started by the root user, and it
68 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
69 case with any command that root executes, you must take care that it is
70 protected from modification by non-root users. Not only must the files
71 themselves be writeable only by root, but so must the directories, and
72 parents of all directories. For example, if you choose to place
73 ServerRoot in <code>/usr/local/apache</code> then it is suggested that
74 you create that directory as root, with commands like these:</p>
76 <div class="example"><p><code>
77 mkdir /usr/local/apache <br />
78 cd /usr/local/apache <br />
79 mkdir bin conf logs <br />
80 chown 0 . bin conf logs <br />
81 chgrp 0 . bin conf logs <br />
82 chmod 755 . bin conf logs
85 <p>It is assumed that <code>/</code>, <code>/usr</code>, and
86 <code>/usr/local</code> are only modifiable by root. When you install the
87 <code class="program"><a href="../programs/httpd.html">httpd</a></code> executable, you should ensure that it is
88 similarly protected:</p>
90 <div class="example"><p><code>
91 cp httpd /usr/local/apache/bin <br />
92 chown 0 /usr/local/apache/bin/httpd <br />
93 chgrp 0 /usr/local/apache/bin/httpd <br />
94 chmod 511 /usr/local/apache/bin/httpd
97 <p>You can create an htdocs subdirectory which is modifiable by other
98 users -- since root never executes any files out of there, and shouldn't
99 be creating files in there.</p>
101 <p>If you allow non-root users to modify any files that root either
102 executes or writes on then you open your system to root compromises.
103 For example, someone could replace the <code class="program"><a href="../programs/httpd.html">httpd</a></code> binary so
104 that the next time you start it, it will execute some arbitrary code. If
105 the logs directory is writeable (by a non-root user), someone could replace
106 a log file with a symlink to some other system file, and then root
107 might overwrite that file with arbitrary data. If the log files
108 themselves are writeable (by a non-root user), then someone may be
109 able to overwrite the log itself with bogus data.</p>
111 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
112 <div class="section">
113 <h2><a name="ssi" id="ssi">Server Side Includes</a></h2>
117 <p>Server Side Includes (SSI) present a server administrator with
118 several potential security risks.</p>
120 <p>The first risk is the increased load on the server. All
121 SSI-enabled files have to be parsed by Apache, whether or not
122 there are any SSI directives included within the files. While this
123 load increase is minor, in a shared server environment it can become
126 <p>SSI files also pose the same risks that are associated with CGI
127 scripts in general. Using the <code>exec cmd</code> element, SSI-enabled
128 files can execute any CGI script or program under the permissions of the
129 user and group Apache runs as, as configured in
130 <code>httpd.conf</code>.</p>
132 <p>There are ways to enhance the security of SSI files while still
133 taking advantage of the benefits they provide.</p>
135 <p>To isolate the damage a wayward SSI file can cause, a server
136 administrator can enable <a href="../suexec.html">suexec</a> as
137 described in the <a href="#cgi">CGI in General</a> section.</p>
139 <p>Enabling SSI for files with <code>.html</code> or <code>.htm</code>
140 extensions can be dangerous. This is especially true in a shared, or high
141 traffic, server environment. SSI-enabled files should have a separate
142 extension, such as the conventional <code>.shtml</code>. This helps keep
143 server load at a minimum and allows for easier management of risk.</p>
145 <p>Another solution is to disable the ability to run scripts and
146 programs from SSI pages. To do this replace <code>Includes</code>
147 with <code>IncludesNOEXEC</code> in the <code class="directive"><a href="../mod/core.html#options">Options</a></code> directive. Note that users may
148 still use <code><--#include virtual="..." --></code> to execute CGI
149 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>
151 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
152 <div class="section">
153 <h2><a name="cgi" id="cgi">CGI in General</a></h2>
157 <p>First of all, you always have to remember that you must trust the
158 writers of the CGI scripts/programs or your ability to spot potential
159 security holes in CGI, whether they were deliberate or accidental. CGI
160 scripts can run essentially arbitrary commands on your system with the
161 permissions of the web server user and can therefore be extremely
162 dangerous if they are not carefully checked.</p>
164 <p>All the CGI scripts will run as the same user, so they have potential
165 to conflict (accidentally or deliberately) with other scripts e.g. User
166 A hates User B, so he writes a script to trash User B's CGI database. One
167 program which can be used to allow scripts to run as different users is
168 <a href="../suexec.html">suEXEC</a> which is included with Apache as of
169 1.2 and is called from special hooks in the Apache server code. Another
170 popular way of doing this is with
171 <a href="http://cgiwrap.unixtools.org/">CGIWrap</a>.</p>
173 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
174 <div class="section">
175 <h2><a name="nsaliasedcgi" id="nsaliasedcgi">Non Script Aliased CGI</a></h2>
179 <p>Allowing users to execute CGI scripts in any directory should only be
183 <li>You trust your users not to write scripts which will deliberately
184 or accidentally expose your system to an attack.</li>
185 <li>You consider security at your site to be so feeble in other areas,
186 as to make one more potential hole irrelevant.</li>
187 <li>You have no users, and nobody ever visits your server.</li>
190 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
191 <div class="section">
192 <h2><a name="saliasedcgi" id="saliasedcgi">Script Aliased CGI</a></h2>
196 <p>Limiting CGI to special directories gives the admin control over what
197 goes into those directories. This is inevitably more secure than non
198 script aliased CGI, but only if users with write access to the
199 directories are trusted or the admin is willing to test each
200 new CGI script/program for potential security holes.</p>
202 <p>Most sites choose this option over the non script aliased CGI
205 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
206 <div class="section">
207 <h2><a name="dynamic" id="dynamic">Other sources of dynamic content</a></h2>
211 <p>Embedded scripting options which run as part of the server itself,
212 such as <code>mod_php</code>, <code>mod_perl</code>, <code>mod_tcl</code>,
213 and <code>mod_python</code>, run under the identity of the server itself
214 (see the <code class="directive"><a href="../mod/mpm_common.html#user">User</a></code> directive), and
215 therefore scripts executed by these engines potentially can access
216 anything the server user can. Some scripting engines may provide
217 restrictions, but it is better to be safe and assume not.</p>
219 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
220 <div class="section">
221 <h2><a name="systemsettings" id="systemsettings">Protecting System Settings</a></h2>
225 <p>To run a really tight ship, you'll want to stop users from setting
226 up <code>.htaccess</code> files which can override security features
227 you've configured. Here's one way to do it.</p>
229 <p>In the server configuration file, put</p>
231 <div class="example"><p><code>
232 <Directory /> <br />
233 AllowOverride None <br />
237 <p>This prevents the use of <code>.htaccess</code> files in all
238 directories apart from those specifically enabled.</p>
240 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
241 <div class="section">
242 <h2><a name="protectserverfiles" id="protectserverfiles">Protect Server Files by Default</a></h2>
246 <p>One aspect of Apache which is occasionally misunderstood is the
247 feature of default access. That is, unless you take steps to change it,
248 if the server can find its way to a file through normal URL mapping
249 rules, it can serve it to clients.</p>
251 <p>For instance, consider the following example:</p>
253 <div class="example"><p><code>
254 # cd /; ln -s / public_html <br />
255 Accessing <code>http://localhost/~root/</code>
258 <p>This would allow clients to walk through the entire filesystem. To
259 work around this, add the following block to your server's
262 <div class="example"><p><code>
263 <Directory /> <br />
264 Order Deny,Allow <br />
269 <p>This will forbid default access to filesystem locations. Add
270 appropriate <code class="directive"><a href="../mod/core.html#directory">Directory</a></code> blocks to
271 allow access only in those areas you wish. For example,</p>
273 <div class="example"><p><code>
274 <Directory /usr/users/*/public_html> <br />
275 Order Deny,Allow <br />
276 Allow from all <br />
277 </Directory> <br />
278 <Directory /usr/local/httpd> <br />
279 Order Deny,Allow <br />
280 Allow from all <br />
284 <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
285 if <code><Directory /></code> denies access, a <code>
286 <Location /></code> directive might overturn it.</p>
288 <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
289 something like <code>./</code> would have the same effect, for root, as
290 the first example above. If you are using Apache 1.3 or above, we strongly
291 recommend that you include the following line in your server
292 configuration files:</p>
294 <div class="example"><p><code>
295 UserDir disabled root
298 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
299 <div class="section">
300 <h2><a name="watchyourlogs" id="watchyourlogs">Watching Your Logs</a></h2>
304 <p>To keep up-to-date with what is actually going on against your server
305 you have to check the <a href="../logs.html">Log Files</a>. Even though
306 the log files only reports what has already happened, they will give you
307 some understanding of what attacks is thrown against the server and
308 allow you to check if the necessary level of security is present.</p>
310 <p>A couple of examples:</p>
312 <div class="example"><p><code>
313 grep -c "/jsp/source.jsp?/jsp/ /jsp/source.jsp??" access_log <br />
314 grep "client denied" error_log | tail -n 10
317 <p>The first example will list the number of attacks trying to exploit the
318 <a href="http://online.securityfocus.com/bid/4876/info/">Apache Tomcat
319 Source.JSP Malformed Request Information Disclosure Vulnerability</a>,
320 the second example will list the ten last denied clients, for example:</p>
322 <div class="example"><p><code>
323 [Thu Jul 11 17:18:39 2002] [error] [client foo.bar.com] client denied
324 by server configuration: /usr/local/apache/htdocs/.htpasswd
327 <p>As you can see, the log files only report what already has happened, so
328 if the client had been able to access the <code>.htpasswd</code> file you
329 would have seen something similar to:</p>
331 <div class="example"><p><code>
332 foo.bar.com - - [12/Jul/2002:01:59:13 +0200] "GET /.htpasswd HTTP/1.1"
335 <p>in your <a href="../logs.html#accesslog">Access Log</a>. This means
336 you probably commented out the following in your server configuration
339 <div class="example"><p><code>
340 <Files ~ "^\.ht"> <br />
341 Order allow,deny <br />
347 <div class="bottomlang">
348 <p><span>Available Languages: </span><a href="../en/misc/security_tips.html" title="English"> en </a> |
349 <a href="../ko/misc/security_tips.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> |
350 <a href="../tr/misc/security_tips.html" hreflang="tr" rel="alternate" title="Türkçe"> tr </a></p>
351 </div><div id="footer">
352 <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>
353 <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>