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 7 --> 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" /><link rel="stylesheet" type="text/css" href="/style/css/prettify.css" /> 12<script src="/style/scripts/prettify.js" type="text/javascript"> 13</script> 14 15<link href="/images/favicon.ico" rel="shortcut icon" /></head> 16<body id="manual-page"><div id="page-header"> 17<p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p> 18<p class="apache">Apache HTTP Server Version 2.2</p> 19<img alt="" src="/images/feather.gif" /></div> 20<div class="up"><a href="./"><img title="<-" alt="<-" src="/images/left.gif" /></a></div> 21<div id="path"> 22<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 2.2</a> > <a href="./">Miscellaneous Documentation</a></div><div id="page-content"><div id="preamble"><h1>Security Tips</h1> 23<div class="toplang"> 24<p><span>Available Languages: </span><a href="/en/misc/security_tips.html" title="English"> en </a> | 25<a href="/ko/misc/security_tips.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | 26<a href="/tr/misc/security_tips.html" hreflang="tr" rel="alternate" title="T�rk�e"> tr </a></p> 27</div> 28 29 <p>Some hints and tips on security issues in setting up a web server. 30 Some of the suggestions will be general, others specific to Apache.</p> 31 </div> 32<div id="quickview"><ul id="toc"><li><img alt="" src="/images/down.gif" /> <a href="#uptodate">Keep up to Date</a></li> 33<li><img alt="" src="/images/down.gif" /> <a href="#serverroot">Permissions on ServerRoot Directories</a></li> 34<li><img alt="" src="/images/down.gif" /> <a href="#ssi">Server Side Includes</a></li> 35<li><img alt="" src="/images/down.gif" /> <a href="#cgi">CGI in General</a></li> 36<li><img alt="" src="/images/down.gif" /> <a href="#nsaliasedcgi">Non Script Aliased CGI</a></li> 37<li><img alt="" src="/images/down.gif" /> <a href="#saliasedcgi">Script Aliased CGI</a></li> 38<li><img alt="" src="/images/down.gif" /> <a href="#dynamic">Other sources of dynamic content</a></li> 39<li><img alt="" src="/images/down.gif" /> <a href="#systemsettings">Protecting System Settings</a></li> 40<li><img alt="" src="/images/down.gif" /> <a href="#protectserverfiles">Protect Server Files by Default</a></li> 41<li><img alt="" src="/images/down.gif" /> <a href="#watchyourlogs">Watching Your Logs</a></li> 42</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div> 43<div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 44<div class="section"> 45<h2><a name="uptodate" id="uptodate">Keep up to Date</a></h2> 46 47 <p>The Apache HTTP Server has a good record for security and a 48 developer community highly concerned about security issues. But 49 it is inevitable that some problems -- small or large -- will be 50 discovered in software after it is released. For this reason, it 51 is crucial to keep aware of updates to the software. If you have 52 obtained your version of the HTTP Server directly from Apache, we 53 highly recommend you subscribe to the <a href="http://httpd.apache.org/lists.html#http-announce">Apache 54 HTTP Server Announcements List</a> where you can keep informed of 55 new releases and security updates. Similar services are available 56 from most third-party distributors of Apache software.</p> 57 58 <p>Of course, most times that a web server is compromised, it is 59 not because of problems in the HTTP Server code. Rather, it comes 60 from problems in add-on code, CGI scripts, or the underlying 61 Operating System. You must therefore stay aware of problems and 62 updates with all the software on your system.</p> 63 64 </div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 65<div class="section"> 66<h2><a name="serverroot" id="serverroot">Permissions on ServerRoot Directories</a></h2> 67 68 69 70 <p>In typical operation, Apache is started by the root user, and it 71 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 72 case with any command that root executes, you must take care that it is 73 protected from modification by non-root users. Not only must the files 74 themselves be writeable only by root, but so must the directories, and 75 parents of all directories. For example, if you choose to place 76 ServerRoot in <code>/usr/local/apache</code> then it is suggested that 77 you create that directory as root, with commands like these:</p> 78 79 <div class="example"><p><code> 80 mkdir /usr/local/apache <br /> 81 cd /usr/local/apache <br /> 82 mkdir bin conf logs <br /> 83 chown 0 . bin conf logs <br /> 84 chgrp 0 . bin conf logs <br /> 85 chmod 755 . bin conf logs 86 </code></p></div> 87 88 <p>It is assumed that <code>/</code>, <code>/usr</code>, and 89 <code>/usr/local</code> are only modifiable by root. When you install the 90 <code class="program"><a href="/programs/httpd.html">httpd</a></code> executable, you should ensure that it is 91 similarly protected:</p> 92 93 <div class="example"><p><code> 94 cp httpd /usr/local/apache/bin <br /> 95 chown 0 /usr/local/apache/bin/httpd <br /> 96 chgrp 0 /usr/local/apache/bin/httpd <br /> 97 chmod 511 /usr/local/apache/bin/httpd 98 </code></p></div> 99 100 <p>You can create an htdocs subdirectory which is modifiable by other 101 users -- since root never executes any files out of there, and shouldn't 102 be creating files in there.</p> 103 104 <p>If you allow non-root users to modify any files that root either 105 executes or writes on then you open your system to root compromises. 106 For example, someone could replace the <code class="program"><a href="/programs/httpd.html">httpd</a></code> binary so 107 that the next time you start it, it will execute some arbitrary code. If 108 the logs directory is writeable (by a non-root user), someone could replace 109 a log file with a symlink to some other system file, and then root 110 might overwrite that file with arbitrary data. If the log files 111 themselves are writeable (by a non-root user), then someone may be 112 able to overwrite the log itself with bogus data.</p> 113 114 </div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 115<div class="section"> 116<h2><a name="ssi" id="ssi">Server Side Includes</a></h2> 117 118 119 120 <p>Server Side Includes (SSI) present a server administrator with 121 several potential security risks.</p> 122 123 <p>The first risk is the increased load on the server. All 124 SSI-enabled files have to be parsed by Apache, whether or not 125 there are any SSI directives included within the files. While this 126 load increase is minor, in a shared server environment it can become 127 significant.</p> 128 129 <p>SSI files also pose the same risks that are associated with CGI 130 scripts in general. Using the <code>exec cmd</code> element, SSI-enabled 131 files can execute any CGI script or program under the permissions of the 132 user and group Apache runs as, as configured in <code>httpd.conf</code>. 133 </p> 134 135 <p>There are ways to enhance the security of SSI files while still 136 taking advantage of the benefits they provide.</p> 137 138 <p>To isolate the damage a wayward SSI file can cause, a server 139 administrator can enable <a href="/suexec.html">suexec</a> as 140 described in the <a href="#cgi">CGI in General</a> section.</p> 141 142 <p>Enabling SSI for files with <code>.html</code> or <code>.htm</code> 143 extensions can be dangerous. This is especially true in a shared, or high 144 traffic, server environment. SSI-enabled files should have a separate 145 extension, such as the conventional <code>.shtml.</code> This helps keep 146 server load at a minimum and allows for easier management of risk.</p> 147 148 <p>Another solution is to disable the ability to run scripts and 149 programs from SSI pages. To do this replace <code>Includes</code> 150 with <code>IncludesNOEXEC</code> in the <code class="directive"><a href="/mod/core.html#options">Options</a></code> directive. Note that users may 151 still use <code><--#include virtual="..." --></code> to execute CGI 152 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> 153 154 </div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 155<div class="section"> 156<h2><a name="cgi" id="cgi">CGI in General</a></h2> 157 158 159 160 <p>First of all, you always have to remember that you must trust the 161 writers of the CGI scripts/programs or your ability to spot potential 162 security holes in CGI, whether they were deliberate or accidental. CGI 163 scripts can run essentially arbitrary commands on your system with the 164 permissions of the web server user and can therefore be extremely 165 dangerous if they are not carefully checked.</p> 166 167 <p>All the CGI scripts will run as the same user, so they have potential 168 to conflict (accidentally or deliberately) with other scripts e.g. User 169 A hates User B, so he writes a script to trash User B's CGI database. One 170 program which can be used to allow scripts to run as different users is 171 <a href="/suexec.html">suEXEC</a> which is included with Apache as of 172 1.2 and is called from special hooks in the Apache server code. Another 173 popular way of doing this is with 174 <a href="http://cgiwrap.sourceforge.net/">CGIWrap</a>.</p> 175 176 </div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 177<div class="section"> 178<h2><a name="nsaliasedcgi" id="nsaliasedcgi">Non Script Aliased CGI</a></h2> 179 180 181 182 <p>Allowing users to execute CGI scripts in any directory should only be 183 considered if:</p> 184 185 <ul> 186 <li>You trust your users not to write scripts which will deliberately 187 or accidentally expose your system to an attack.</li> 188 <li>You consider security at your site to be so feeble in other areas, 189 as to make one more potential hole irrelevant.</li> 190 <li>You have no users, and nobody ever visits your server.</li> 191 </ul> 192 193 </div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 194<div class="section"> 195<h2><a name="saliasedcgi" id="saliasedcgi">Script Aliased CGI</a></h2> 196 197 198 199 <p>Limiting CGI to special directories gives the admin control over what 200 goes into those directories. This is inevitably more secure than non 201 script aliased CGI, but only if users with write access to the 202 directories are trusted or the admin is willing to test each 203 new CGI script/program for potential security holes.</p> 204 205 <p>Most sites choose this option over the non script aliased CGI 206 approach.</p> 207 208 </div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 209<div class="section"> 210<h2><a name="dynamic" id="dynamic">Other sources of dynamic content</a></h2> 211 212 213 214 <p> 215 Embedded scripting options which run as part of the server itself, 216 such as <code>mod_php</code>, <code>mod_perl</code>, <code>mod_tcl</code>, 217 and <code>mod_python</code>, run under the identity of the server itself 218 (see the <code class="directive"><a href="/mod/mpm_common.html#user">User</a></code> directive), and 219 therefore scripts executed by these engines potentially can access anything 220 the server user can. Some scripting engines may provide restrictions, but 221 it is better to be safe and assume not.</p> 222 223 </div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 224<div class="section"> 225<h2><a name="systemsettings" id="systemsettings">Protecting System Settings</a></h2> 226 227 228 229 <p>To run a really tight ship, you'll want to stop users from setting 230 up <code>.htaccess</code> files which can override security features 231 you've configured. Here's one way to do it.</p> 232 233 <p>In the server configuration file, put</p> 234 235 <div class="example"><p><code> 236 <Directory /> <br /> 237 AllowOverride None <br /> 238 </Directory> 239 </code></p></div> 240 241 <p>This prevents the use of <code>.htaccess</code> files in all 242 directories apart from those specifically enabled.</p> 243 244 </div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 245<div class="section"> 246<h2><a name="protectserverfiles" id="protectserverfiles">Protect Server Files by Default</a></h2> 247 248 249 250 <p>One aspect of Apache which is occasionally misunderstood is the 251 feature of default access. That is, unless you take steps to change it, 252 if the server can find its way to a file through normal URL mapping 253 rules, it can serve it to clients.</p> 254 255 <p>For instance, consider the following example:</p> 256 257 <div class="example"><p><code> 258 # cd /; ln -s / public_html <br /> 259 Accessing <code>http://localhost/~root/</code> 260 </code></p></div> 261 262 <p>This would allow clients to walk through the entire filesystem. To 263 work around this, add the following block to your server's 264 configuration:</p> 265 266 <div class="example"><p><code> 267 <Directory /> <br /> 268 Order Deny,Allow <br /> 269 Deny from all <br /> 270 </Directory> 271 </code></p></div> 272 273 <p>This will forbid default access to filesystem locations. Add 274 appropriate <code class="directive"><a href="/mod/core.html#directory">Directory</a></code> blocks to 275 allow access only in those areas you wish. For example,</p> 276 277 <div class="example"><p><code> 278 <Directory /usr/users/*/public_html> <br /> 279 Order Deny,Allow <br /> 280 Allow from all <br /> 281 </Directory> <br /> 282 <Directory /usr/local/httpd> <br /> 283 Order Deny,Allow <br /> 284 Allow from all <br /> 285 </Directory> 286 </code></p></div> 287 288 <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 289 if <code><Directory /></code> denies access, a <code> 290 <Location /></code> directive might overturn it.</p> 291 292 <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 293 something like <code>./</code> would have the same effect, for root, as 294 the first example above. If you are using Apache 1.3 or above, we strongly 295 recommend that you include the following line in your server 296 configuration files:</p> 297 298 <div class="example"><p><code> 299 UserDir disabled root 300 </code></p></div> 301 302 </div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div> 303<div class="section"> 304<h2><a name="watchyourlogs" id="watchyourlogs">Watching Your Logs</a></h2> 305 306 307 308 <p>To keep up-to-date with what is actually going on against your server 309 you have to check the <a href="/logs.html">Log Files</a>. Even though 310 the log files only reports what has already happened, they will give you 311 some understanding of what attacks is thrown against the server and 312 allow you to check if the necessary level of security is present.</p> 313 314 <p>A couple of examples:</p> 315 316 <div class="example"><p><code> 317 grep -c "/jsp/source.jsp?/jsp/ /jsp/source.jsp??" access_log <br /> 318 grep "client denied" error_log | tail -n 10 319 </code></p></div> 320 321 <p>The first example will list the number of attacks trying to exploit the 322 <a href="http://online.securityfocus.com/bid/4876/info/">Apache Tomcat 323 Source.JSP Malformed Request Information Disclosure Vulnerability</a>, 324 the second example will list the ten last denied clients, for example:</p> 325 326 <div class="example"><p><code> 327 [Thu Jul 11 17:18:39 2002] [error] [client foo.example.com] client denied 328 by server configuration: /usr/local/apache/htdocs/.htpasswd 329 </code></p></div> 330 331 <p>As you can see, the log files only report what already has happened, so 332 if the client had been able to access the <code>.htpasswd</code> file you 333 would have seen something similar to:</p> 334 335 <div class="example"><p><code> 336 foo.example.com - - [12/Jul/2002:01:59:13 +0200] "GET /.htpasswd HTTP/1.1" 337 </code></p></div> 338 339 <p>in your <a href="/logs.html#accesslog">Access Log</a>. This means 340 you probably commented out the following in your server configuration 341 file:</p> 342 343 <div class="example"><p><code> 344 <Files ~ "^\.ht"> <br /> 345 Order allow,deny <br /> 346 Deny from all <br /> 347 </Files> 348 </code></p></div> 349 350 </div></div> 351<div class="bottomlang"> 352<p><span>Available Languages: </span><a href="/en/misc/security_tips.html" title="English"> en </a> | 353<a href="/ko/misc/security_tips.html" hreflang="ko" rel="alternate" title="Korean"> ko </a> | 354<a href="/tr/misc/security_tips.html" hreflang="tr" rel="alternate" title="T�rk�e"> tr </a></p> 355</div><div class="top"><a href="#page-header"><img src="/images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. 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