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From erikab...@apache.org
Subject cvs commit: httpd-2.0/docs/manual/misc security_tips.html.en security_tips.xml security_tips.html
Date Fri, 23 Aug 2002 21:02:16 GMT
erikabele    2002/08/23 14:02:16

  Added:       docs/manual/misc security_tips.html.en security_tips.xml
  Removed:     docs/manual/misc security_tips.html
  Log:
  New XML.
  
  Submitted by: David Shane Holden <dpejesh@yahoo.com>
  
  Revision  Changes    Path
  1.1                  httpd-2.0/docs/manual/misc/security_tips.html.en
  
  Index: security_tips.html.en
  ===================================================================
  <html><head><META http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><!--
          XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
                This file is generated from xml source: DO NOT EDIT
          XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
        --><title>Security Tips - Apache HTTP Server</title><link href="../style/manual.css"
type="text/css" rel="stylesheet"></head><body><blockquote><div align="center"><img
src="../images/sub.gif" alt="[APACHE DOCUMENTATION]"><h3>Apache HTTP Server Version
2.0</h3></div><h1 align="center">Security Tips</h1>
      <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>
    <ul><li><a href="#serverroot">Permissions on ServerRoot Directories</a></li><li><a
href="#ssi">Server Side Includes</a></li><li><a href="#cgi">CGI
in General</a></li><li><a href="#nsaliasedcgi">Non Script Aliased
CGI</a></li><li><a href="#saliasedcgi">Script Aliased CGI</a></li><li><a
href="#systemsettings">Protecting System Settings</a></li><li><a href="#protectserverfiles">Protect
Server Files by Default</a></li><li><a href="#watchyourlogs">Watching
Your Logs</a></li></ul><hr><h2><a name="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 <a href="../mod/mpm_common.html#user" class="directive"><code
class="directive">User</code></a> 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  /usr/local/apache then it is suggested that you create 
      that directory as root, with commands like these:</p>
      
      <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><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></td></tr></table></blockquote>
      
      <p>It is assumed that /, /usr, and /usr/local are only modifiable by 
      root. When you install the httpd executable, you should ensure that 
      it is similarly protected:</p>
      
      <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><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></td></tr></table></blockquote>
      
      <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 httpd 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>
      
    <h2><a name="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 "exec cmd" 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 httpd.conf.</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 .html or .htm 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 .shtml. 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 <a href="../mod/core.html#options"
class="directive"><code class="directive">Options</code></a> directive.
 Note that users may 
      still use &gt;--#include virtual="..." --&lt; to execute CGI scripts if 
      these scripts are in directories desginated by a <a href="../mod/mod_alias.html#scriptalias"
class="directive"><code class="directive">ScriptAlias</code></a> directive.</p>
      
    <h2><a name="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>
      
    <h2><a name="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>
      
    <h2><a name="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>
      
    <h2><a name="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>
      
      <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
        &lt;Directory /&gt; <br>
          AllowOverride None <br>
        &lt;/Directory&gt;
      </code></td></tr></table></blockquote>
      
      <p>This prevents the use of <code>.htaccess</code> files in all 
      directories apart from those specifically enabled.</p>
      
    <h2><a name="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>
      
      <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
        # cd /; ln -s / public_html <br>
        Accessing <code>http://localhost/~root/</code>
      </code></td></tr></table></blockquote>
      
      <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>
      
      <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
        &lt;Directory /&gt; <br>
        Order Deny,Allow <br>
        Deny from all <br>
        &lt;/Directory&gt;
      </code></td></tr></table></blockquote>
      
      <p>This will forbid default access to filesystem locations. Add 
      appropriate <a href="../mod/core.html#directory" class="directive"><code class="directive">Directory</code></a>
blocks to 
      allow access only in those areas you wish. For example,</p>
      
      <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><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></td></tr></table></blockquote>
      
      <p>Pay particular attention to the interactions of <a href="../mod/core.html#location"
class="directive"><code class="directive">Location</code></a> and <a
href="../mod/core.html#directory" class="directive"><code class="directive">Directory</code></a>
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 <a href="../mod/mod_userdir.html#userdir"
class="directive"><code class="directive">UserDir</code></a> directive;
setting it to 
      something like "./" 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>
      
      <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
        UserDir disabled root
      </code></td></tr></table></blockquote>
      
    <h2><a name="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 happend, they will give you 
      some understanding of what attacks is thrown against the server and 
      allows you to check if the necessary level of security is present.</p>
      
      <p>A couple of examples:</p>
      
      <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
        grep -c "/jsp/source.jsp?/jsp/ /jsp/source.jsp??" access_log <br>
        grep "client denied" error_log | tail -n 10
      </code></td></tr></table></blockquote>
      
      <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>
      
      <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
        [Thu Jul 11 17:18:39 2002] [error] [client foo.bar.com] client denied 
        by server configuration: /usr/local/apache/htdocs/.htpasswd
      </code></td></tr></table></blockquote>
      
      <p>As you can see, the log files only report what already has happend, so 
      if the client had been able to access the <code>.htpasswd</code> file you

      would have seen something similar to:</p>
      
      <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
        foo.bar.com - - [12/Jul/2002:01:59:13 +0200] "GET /.htpasswd HTTP/1.1"
      </code></td></tr></table></blockquote>
      
      <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>
      
      <blockquote><table cellpadding="10"><tr><td bgcolor="#eeeeee"><code>
        &lt;Files ~ "^\.ht"&gt; <br>
          Order allow,deny <br>
          Deny from all <br>
        &lt;Files&gt;
      </code></td></tr></table></blockquote>
      
    <hr></blockquote><h3 align="center">Apache HTTP Server Version 2.0</h3><a
href="./"><img src="../images/index.gif" alt="Index"></a><a href="../"><img
src="../images/home.gif" alt="Home"></a></body></html>
  
  
  1.1                  httpd-2.0/docs/manual/misc/security_tips.xml
  
  Index: security_tips.xml
  ===================================================================
  <?xml version="1.0" encoding="UTF-8" ?>
  <!DOCTYPE manualpage SYSTEM "../style/manualpage.dtd">
  <?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
  
  <manualpage>
    <relativepath href=".." />
  
    <title>Security Tips</title>
    
    <summary>
      <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>
    </summary>
    
    <section id="serverroot">
    
      <title>Permissions on ServerRoot Directories</title>
      
      <p>In typical operation, Apache is started by the root user, and it 
      switches to the user defined by the <directive 
      module="mpm_common">User</directive> 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  /usr/local/apache then it is suggested that you create 
      that directory as root, with commands like these:</p>
      
      <example>
        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
      </example>
      
      <p>It is assumed that /, /usr, and /usr/local are only modifiable by 
      root. When you install the httpd executable, you should ensure that 
      it is similarly protected:</p>
      
      <example>
        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
      </example>
      
      <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 httpd 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>
      
    </section>
    
    <section id="ssi">
    
      <title>Server Side Includes</title>
      
      <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 "exec cmd" 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 httpd.conf.</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 .html or .htm 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 .shtml. 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 <directive
      module="core">Options</directive> directive.  Note that users may 
      still use &gt;--#include virtual="..." --&lt; to execute CGI scripts if 
      these scripts are in directories desginated by a <directive
      module="mod_alias">ScriptAlias</directive> directive.</p>
      
    </section>
    
    <section id="cgi">
    
      <title>CGI in General</title>
      
      <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>
      
    </section>
    
    <section id="nsaliasedcgi">
    
      <title>Non Script Aliased CGI</title>
      
      <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>
      
    </section>
    
    <section id="saliasedcgi">
    
      <title>Script Aliased CGI</title>
      
      <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>
      
    </section>
    
    <section id="systemsettings">
    
      <title>Protecting System Settings</title>
      
      <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>
      
      <example>
        &lt;Directory /&gt; <br />
          AllowOverride None <br />
        &lt;/Directory&gt;
      </example>
      
      <p>This prevents the use of <code>.htaccess</code> files in all 
      directories apart from those specifically enabled.</p>
      
    </section>
    
    <section id="protectserverfiles">
    
      <title>Protect Server Files by Default</title>
      
      <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>
      
      <example>
        # cd /; ln -s / public_html <br />
        Accessing <code>http://localhost/~root/</code>
      </example>
      
      <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>
      
      <example>
        &lt;Directory /&gt; <br />
        Order Deny,Allow <br />
        Deny from all <br />
        &lt;/Directory&gt;
      </example>
      
      <p>This will forbid default access to filesystem locations. Add 
      appropriate <directive module="core">Directory</directive> blocks to 
      allow access only in those areas you wish. For example,</p>
      
      <example>
        &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;
      </example>
      
      <p>Pay particular attention to the interactions of <directive
      module="core">Location</directive> and <directive 
      module="core">Directory</directive> 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 <directive
      module="mod_userdir">UserDir</directive> directive; setting it to 
      something like "./" 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>
      
      <example>
        UserDir disabled root
      </example>
      
    </section>
    
    <section id="watchyourlogs">
    
      <title>Watching Your Logs</title>
      
      <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 happend, they will give you 
      some understanding of what attacks is thrown against the server and 
      allows you to check if the necessary level of security is present.</p>
      
      <p>A couple of examples:</p>
      
      <example>
        grep -c "/jsp/source.jsp?/jsp/ /jsp/source.jsp??" access_log <br />
        grep "client denied" error_log | tail -n 10
      </example>
      
      <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>
      
      <example>
        [Thu Jul 11 17:18:39 2002] [error] [client foo.bar.com] client denied 
        by server configuration: /usr/local/apache/htdocs/.htpasswd
      </example>
      
      <p>As you can see, the log files only report what already has happend, so 
      if the client had been able to access the <code>.htpasswd</code> file you

      would have seen something similar to:</p>
      
      <example>
        foo.bar.com - - [12/Jul/2002:01:59:13 +0200] "GET /.htpasswd HTTP/1.1"
      </example>
      
      <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>
      
      <example>
        &lt;Files ~ "^\.ht"&gt; <br />
          Order allow,deny <br />
          Deny from all <br />
        &lt;Files&gt;
      </example>
      
    </section>
    
  </manualpage>
  
  
  

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