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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter�18.�Securing Samba</title><link rel="stylesheet" href="../samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.74.0"><link rel="home" href="index.html" title="The Official Samba 3.4.x HOWTO and Reference Guide"><link rel="up" href="optional.html" title="Part�III.�Advanced Configuration"><link rel="prev" href="locking.html" title="Chapter�17.�File and Record Locking"><link rel="next" href="InterdomainTrusts.html" title="Chapter�19.�Interdomain Trust Relationships"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter�18.�Securing Samba</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="locking.html">Prev</a>�</td><th width="60%" align="center">Part�III.�Advanced Configuration</th><td width="20%" align="right">�<a accesskey="n" href="InterdomainTrusts.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="securing-samba"></a>Chapter�18.�Securing Samba</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Andrew</span> <span class="orgname">Samba Team</span> <span class="surname">Tridgell</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><code class="email"><<a class="email" href="mailto:tridge@samba.org">tridge@samba.org</a>></code></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">John</span> <span class="othername">H.</span> <span class="orgname">Samba Team</span> <span class="surname">Terpstra</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><code class="email"><<a class="email" href="mailto:jht@samba.org">jht@samba.org</a>></code></p></div></div></div></div><div><p class="pubdate">May 26, 2003</p></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="securing-samba.html#id2618075">Introduction</a></span></dt><dt><span class="sect1"><a href="securing-samba.html#id2618174">Features and Benefits</a></span></dt><dt><span class="sect1"><a href="securing-samba.html#id2618320">Technical Discussion of Protective Measures and Issues</a></span></dt><dd><dl><dt><span class="sect2"><a href="securing-samba.html#id2618336">Using Host-Based Protection</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id2618490">User-Based Protection</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id2618550">Using Interface Protection</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#firewallports">Using a Firewall</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id2618900">Using IPC$ Share-Based Denials </a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id2619044">NTLMv2 Security</a></span></dt></dl></dd><dt><span class="sect1"><a href="securing-samba.html#id2619099">Upgrading Samba</a></span></dt><dt><span class="sect1"><a href="securing-samba.html#id2619142">Common Errors</a></span></dt><dd><dl><dt><span class="sect2"><a href="securing-samba.html#id2619158">Smbclient Works on Localhost, but the Network Is Dead</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id2619187">Why Can Users Access Other Users' Home Directories?</a></span></dt></dl></dd></dl></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2618075"></a>Introduction</h2></div></div></div><p>
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<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter�18.�Securing Samba</title><link rel="stylesheet" href="../samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.75.2"><link rel="home" href="index.html" title="The Official Samba 3.4.x HOWTO and Reference Guide"><link rel="up" href="optional.html" title="Part�III.�Advanced Configuration"><link rel="prev" href="locking.html" title="Chapter�17.�File and Record Locking"><link rel="next" href="InterdomainTrusts.html" title="Chapter�19.�Interdomain Trust Relationships"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Chapter�18.�Securing Samba</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="locking.html">Prev</a>�</td><th width="60%" align="center">Part�III.�Advanced Configuration</th><td width="20%" align="right">�<a accesskey="n" href="InterdomainTrusts.html">Next</a></td></tr></table><hr></div><div class="chapter" title="Chapter�18.�Securing Samba"><div class="titlepage"><div><div><h2 class="title"><a name="securing-samba"></a>Chapter�18.�Securing Samba</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Andrew</span> <span class="surname">Tridgell</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><code class="email"><<a class="email" href="mailto:tridge@samba.org">tridge@samba.org</a>></code></p></div></div></div></div><div><div class="author"><h3 class="author"><span class="firstname">John</span> <span class="othername">H.</span> <span class="surname">Terpstra</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><code class="email"><<a class="email" href="mailto:jht@samba.org">jht@samba.org</a>></code></p></div></div></div></div><div><p class="pubdate">May 26, 2003</p></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="sect1"><a href="securing-samba.html#id2624168">Introduction</a></span></dt><dt><span class="sect1"><a href="securing-samba.html#id2624266">Features and Benefits</a></span></dt><dt><span class="sect1"><a href="securing-samba.html#id2624413">Technical Discussion of Protective Measures and Issues</a></span></dt><dd><dl><dt><span class="sect2"><a href="securing-samba.html#id2624429">Using Host-Based Protection</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id2624583">User-Based Protection</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id2624642">Using Interface Protection</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#firewallports">Using a Firewall</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id2624993">Using IPC$ Share-Based Denials </a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id2625141">NTLMv2 Security</a></span></dt></dl></dd><dt><span class="sect1"><a href="securing-samba.html#id2625196">Upgrading Samba</a></span></dt><dt><span class="sect1"><a href="securing-samba.html#id2625240">Common Errors</a></span></dt><dd><dl><dt><span class="sect2"><a href="securing-samba.html#id2625255">Smbclient Works on Localhost, but the Network Is Dead</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id2625284">Why Can Users Access Other Users' Home Directories?</a></span></dt></dl></dd></dl></div><div class="sect1" title="Introduction"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2624168"></a>Introduction</h2></div></div></div><p>
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The information contained in this chapter applies in general to all Samba installations. Security is
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everyone's concern in the information technology world. A surprising number of Samba servers are being
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installed on machines that have direct internet access, thus security is made more critical than it would have been had the
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server been located behind a firewall and on a private network. Paranoia regarding server security is causing
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some network administrators to insist on the installation of robust firewalls even on servers that are located
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inside secured networks. This chapter provides information to assist the administrator who understands
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how to create the needed barriers and deterents against “<span class="quote">the enemy</span>”, no matter where [s]he may
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how to create the needed barriers and deterents against <span class="quote">“<span class="quote">the enemy</span>”</span>, no matter where [s]he may
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</p><div class="blockquote"><blockquote class="blockquote"><p>
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A new apprentice reported for duty to the chief engineer of a boiler house. He said, “<span class="quote">Here I am,
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if you will show me the boiler I'll start working on it.</span>” Then engineer replied, “<span class="quote">You're leaning
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A new apprentice reported for duty to the chief engineer of a boiler house. He said, <span class="quote">“<span class="quote">Here I am,
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if you will show me the boiler I'll start working on it.</span>”</span> Then engineer replied, <span class="quote">“<span class="quote">You're leaning
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on it!</span>”</span>
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</p></blockquote></div><p>
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Security concerns are just like that. You need to know a little about the subject to appreciate
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how obvious most of it really is. The challenge for most of us is to discover that first morsel
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of knowledge with which we may unlock the secrets of the masters.
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</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2618174"></a>Features and Benefits</h2></div></div></div><p>
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</p></div><div class="sect1" title="Features and Benefits"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2624266"></a>Features and Benefits</h2></div></div></div><p>
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There are three levels at which security principles must be observed in order to render a site
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at least moderately secure. They are the perimeter firewall, the configuration of the host
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server that is running Samba, and Samba itself.
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Samba permits a most flexible approach to network security. As far as possible Samba implements
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the latest protocols to permit more secure MS Windows file and print operations.
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Samba can be secured from connections that originate from outside the local network. This can be done using
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<span class="emphasis"><em>host-based protection</em></span>, using Samba's implementation of a technology known as
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“<span class="quote">tcpwrappers,</span>” or it may be done be using <span class="emphasis"><em>interface-based exclusion</em></span> so
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<span class="quote">“<span class="quote">tcpwrappers,</span>”</span> or it may be done be using <span class="emphasis"><em>interface-based exclusion</em></span> so
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<span class="application">smbd</span> will bind only to specifically permitted interfaces. It is also possible to set specific share- or
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resource-based exclusions, for example, on the <em class="parameter"><code>[IPC$]</code></em> autoshare. The <em class="parameter"><code>[IPC$]</code></em> share is used for browsing purposes as well as to establish TCP/IP connections.
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Another method by which Samba may be secured is by setting Access Control Entries (ACEs) in an Access
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Control List (ACL) on the shares themselves. This is discussed in
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<a class="link" href="AccessControls.html" title="Chapter�16.�File, Directory, and Share Access Controls">File, Directory, and Share Access Controls</a>.
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</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2618320"></a>Technical Discussion of Protective Measures and Issues</h2></div></div></div><p>
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</p></div><div class="sect1" title="Technical Discussion of Protective Measures and Issues"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2624413"></a>Technical Discussion of Protective Measures and Issues</h2></div></div></div><p>
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The key challenge of security is that protective measures suffice at best
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only to close the door on known exploits and breach techniques. Never assume that
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because you have followed these few measures, the Samba server is now an impenetrable
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fortress! Given the history of information systems so far, it is only a matter of time
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before someone will find yet another vulnerability.
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</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2618336"></a>Using Host-Based Protection</h3></div></div></div><p>
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</p><div class="sect2" title="Using Host-Based Protection"><div class="titlepage"><div><div><h3 class="title"><a name="id2624429"></a>Using Host-Based Protection</h3></div></div></div><p>
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In many installations of Samba, the greatest threat comes from outside
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your immediate network. By default, Samba accepts connections from
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any host, which means that if you run an insecure version of Samba on
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a host that is directly connected to the Internet, you can be
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especially vulnerable.
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One of the simplest fixes in this case is to use the <a class="link" href="smb.conf.5.html#HOSTSALLOW" target="_top">hosts allow</a> and
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<a class="link" href="smb.conf.5.html#HOSTSDENY" target="_top">hosts deny</a> options in the Samba <code class="filename">smb.conf</code> configuration file to
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allow access to your server only from a specific range of hosts. An example might be:
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</p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2618426"></a><em class="parameter"><code>hosts allow = 127.0.0.1 192.168.2.0/24 192.168.3.0/24</code></em></td></tr><tr><td><a class="indexterm" name="id2618438"></a><em class="parameter"><code>hosts deny = 0.0.0.0/0</code></em></td></tr></table><p>
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</p><table border="0" summary="Simple list" class="simplelist"><tr><td><a class="indexterm" name="id2624519"></a><em class="parameter"><code>hosts allow = 127.0.0.1 192.168.2.0/24 192.168.3.0/24</code></em></td></tr><tr><td><a class="indexterm" name="id2624531"></a><em class="parameter"><code>hosts deny = 0.0.0.0/0</code></em></td></tr></table><p>
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The above will allow SMB connections only from <code class="constant">localhost</code> (your own
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computer) and from the two private networks 192.168.2 and 192.168.3. All other
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connections will be refused as soon as the client sends its first packet. The refusal
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will be marked as <code class="literal">not listening on called name</code> error.
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</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2618490"></a>User-Based Protection</h3></div></div></div><p>
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</p></div><div class="sect2" title="User-Based Protection"><div class="titlepage"><div><div><h3 class="title"><a name="id2624583"></a>User-Based Protection</h3></div></div></div><p>
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If you want to restrict access to your server to valid users only, then the following
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method may be of use. In the <code class="filename">smb.conf</code> <em class="parameter"><code>[global]</code></em> section put:
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</p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2618518"></a><em class="parameter"><code>valid users = @smbusers, jacko</code></em></td></tr></table><p>
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</p><table border="0" summary="Simple list" class="simplelist"><tr><td><a class="indexterm" name="id2624610"></a><em class="parameter"><code>valid users = @smbusers, jacko</code></em></td></tr></table><p>
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This restricts all server access either to the user <span class="emphasis"><em>jacko</em></span>
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or to members of the system group <span class="emphasis"><em>smbusers</em></span>.
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</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2618550"></a>Using Interface Protection</h3></div></div></div><p>
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</p></div><div class="sect2" title="Using Interface Protection"><div class="titlepage"><div><div><h3 class="title"><a name="id2624642"></a>Using Interface Protection</h3></div></div></div><p>
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By default, Samba accepts connections on any network interface that
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it finds on your system. That means if you have an ISDN line or a PPP
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connection to the Internet then Samba will accept connections on those
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links. This may not be what you want.
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You can change this behavior using options like this:
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</p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id2618593"></a><em class="parameter"><code>interfaces = eth* lo</code></em></td></tr><tr><td><a class="indexterm" name="id2618604"></a><em class="parameter"><code>bind interfaces only = yes</code></em></td></tr></table><p>
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</p><table border="0" summary="Simple list" class="simplelist"><tr><td><a class="indexterm" name="id2624685"></a><em class="parameter"><code>interfaces = eth* lo</code></em></td></tr><tr><td><a class="indexterm" name="id2624697"></a><em class="parameter"><code>bind interfaces only = yes</code></em></td></tr></table><p>
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This tells Samba to listen for connections only on interfaces with a name starting with
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<code class="constant">eth</code> such as <code class="constant">eth0</code> or <code class="constant">eth1</code>, plus on the loopback interface called
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<code class="constant">lo</code>. The name you will need to use depends on what OS you are using. In the above, I used
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the common name for Ethernet adapters on Linux.
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If you use the above and someone tries to make an SMB connection to your host over a PPP interface called
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<code class="constant">ppp0</code>, then [s]he will get a TCP connection refused reply. In that case, no Samba code
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is run at all, because the operating system has been told not to pass connections from that interface to any
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Samba process. However, the refusal helps a would-be cracker by confirming that the IP address provides
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valid active services.
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A better response would be to ignore the connection (from, for example, ppp0) altogether. The
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advantage of ignoring the connection attempt, as compared with refusing it, is that it foils those who
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probe an interface with the sole intention of finding valid IP addresses for later use in exploitation
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or denial of service attacks. This method of dealing with potential malicious activity demands the
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use of appropriate firewall mechanisms.
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</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="firewallports"></a>Using a Firewall</h3></div></div></div><p>
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</p></div><div class="sect2" title="Using a Firewall"><div class="titlepage"><div><div><h3 class="title"><a name="firewallports"></a>Using a Firewall</h3></div></div></div><p>
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Many people use a firewall to deny access to services they do not want exposed outside their network. This can
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be a good idea, although I recommend using it in conjunction with the above methods so you are protected even
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if your firewall is not active for some reason.
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If you are setting up a firewall, you need to know what TCP and UDP ports to allow and block. Samba uses
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</p><table class="simplelist" border="0" summary="Simple list"><tr><td>Port 135/TCP - used by smbd</td></tr><tr><td>Port 137/UDP - used by nmbd</td></tr><tr><td>Port 138/UDP - used by nmbd</td></tr><tr><td>Port 139/TCP - used by smbd</td></tr><tr><td>Port 445/TCP - used by smbd</td></tr></table><p>
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</p><table border="0" summary="Simple list" class="simplelist"><tr><td>Port 135/TCP - used by smbd</td></tr><tr><td>Port 137/UDP - used by nmbd</td></tr><tr><td>Port 138/UDP - used by nmbd</td></tr><tr><td>Port 139/TCP - used by smbd</td></tr><tr><td>Port 445/TCP - used by smbd</td></tr></table><p>
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The last one is important because many older firewall setups may not be aware of it, given that this port
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was only added to the protocol in recent years.
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When configuring a firewall, the high order ports (1024-65535) are often used for outgoing connections and
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therefore should be permitted through the firewall. It is prudent to block incoming packets on the high order
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ports except for established connections.
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</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2618900"></a>Using IPC$ Share-Based Denials </h3></div></div></div><p>
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</p></div><div class="sect2" title="Using IPC$ Share-Based Denials"><div class="titlepage"><div><div><h3 class="title"><a name="id2624993"></a>Using IPC$ Share-Based Denials </h3></div></div></div><p>
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If the above methods are not suitable, then you could also place a more specific deny on the IPC$ share that
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is used in the recently discovered security hole. This allows you to offer access to other shares while
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denying access to IPC$ from potentially untrustworthy hosts.
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To do this you could use:
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</p><table class="simplelist" border="0" summary="Simple list"><tr><td> </td></tr><tr><td><em class="parameter"><code>[IPC$]</code></em></td></tr><tr><td><a class="indexterm" name="id2618952"></a><em class="parameter"><code>hosts allow = 192.168.115.0/24 127.0.0.1</code></em></td></tr><tr><td><a class="indexterm" name="id2618964"></a><em class="parameter"><code>hosts deny = 0.0.0.0/0</code></em></td></tr></table><p>
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</p><table border="0" summary="Simple list" class="simplelist"><tr><td> </td></tr><tr><td><em class="parameter"><code>[IPC$]</code></em></td></tr><tr><td><a class="indexterm" name="id2625049"></a><em class="parameter"><code>hosts allow = 192.168.115.0/24 127.0.0.1</code></em></td></tr><tr><td><a class="indexterm" name="id2625061"></a><em class="parameter"><code>hosts deny = 0.0.0.0/0</code></em></td></tr></table><p>
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This instructs Samba that IPC$ connections are not allowed from anywhere except the two listed network
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addresses (localhost and the 192.168.115 subnet). Connections to other shares are still allowed. Because the
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IPC$ share is the only share that is always accessible anonymously, this provides some level of protection
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against attackers who do not know a valid username/password for your host.
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If you use this method, then clients will be given an <code class="literal">`access denied'</code> reply when they try
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to access the IPC$ share. Those clients will not be able to browse shares and may also be unable to access
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some other resources. This is not recommended unless for some reason you cannot use one of the other methods
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</p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2619044"></a>NTLMv2 Security</h3></div></div></div><p>
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</p></div><div class="sect2" title="NTLMv2 Security"><div class="titlepage"><div><div><h3 class="title"><a name="id2625141"></a>NTLMv2 Security</h3></div></div></div><p>
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To configure NTLMv2 authentication, the following registry keys are worth knowing about:
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