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-<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 24. Securing Samba</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.59.1"><link rel="home" href="index.html" title="SAMBA Project Documentation"><link rel="up" href="optional.html" title="Part III. Advanced Configuration"><link rel="previous" href="integrate-ms-networks.html" title="Chapter 23. Integrating MS Windows networks with Samba"><link rel="next" href="unicode.html" title="Chapter 25. Unicode/Charsets"></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 24. Securing Samba</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="integrate-ms-networks.html">Prev</a> </td><th width="60%" align="center">Part III. Advanced Configuration</th><td width="20%" align="right"> <a accesskey="n" href="unicode.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><h2 class="title"><a name="securing-samba"></a>Chapter 24. Securing Samba</h2></div><div><div class="author"><h3 class="author">Andrew Tridgell</h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt>&lt;<a href="mailto:tridge@samba.org">tridge@samba.org</a>&gt;</tt></p></div></div></div></div><div><div class="author"><h3 class="author">John H. Terpstra</h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><tt>&lt;<a href="mailto:jht@samba.org">jht@samba.org</a>&gt;</tt></p></div></div></div></div><div><p class="pubdate">17 March 2003</p></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><a href="securing-samba.html#id2900501">Introduction</a></dt><dt><a href="securing-samba.html#id2900517">Using host based protection</a></dt><dt><a href="securing-samba.html#id2900967">Using interface protection</a></dt><dt><a href="securing-samba.html#id2901018">Using a firewall</a></dt><dt><a href="securing-samba.html#id2901061">Using a IPC$ share deny</a></dt><dt><a href="securing-samba.html#id2900617">NTLMv2 Security</a></dt><dt><a href="securing-samba.html#id2900653">Upgrading Samba</a></dt></dl></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2900501"></a>Introduction</h2></div></div><p>
+<html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>Chapter 15. Securing Samba</title><link rel="stylesheet" href="samba.css" type="text/css"><meta name="generator" content="DocBook XSL Stylesheets V1.60.1"><link rel="home" href="index.html" title="SAMBA Project Documentation"><link rel="up" href="optional.html" title="Part III. Advanced Configuration"><link rel="previous" href="locking.html" title="Chapter 14. File and Record Locking"><link rel="next" href="InterdomainTrusts.html" title="Chapter 16. 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 15. 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 15. 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><tt class="email">&lt;<a href="mailto:tridge@samba.org">tridge@samba.org</a>&gt;</tt></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><tt class="email">&lt;<a href="mailto:jht@samba.org">jht@samba.org</a>&gt;</tt></p></div></div></div></div><div><p class="pubdate">May 26, 2003</p></div></div><div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><a href="securing-samba.html#id2929518">Introduction</a></dt><dt><a href="securing-samba.html#id2929550">Features and Benefits</a></dt><dt><a href="securing-samba.html#id2928211">Technical Discussion of Protective Measures and Issues</a></dt><dd><dl><dt><a href="securing-samba.html#id2928229">Using host based protection</a></dt><dt><a href="securing-samba.html#id2928297">User based protection</a></dt><dt><a href="securing-samba.html#id2928349">Using interface protection</a></dt><dt><a href="securing-samba.html#id2928399">Using a firewall</a></dt><dt><a href="securing-samba.html#id2928455">Using a IPC$ share deny</a></dt><dt><a href="securing-samba.html#id2928521">NTLMv2 Security</a></dt></dl></dd><dt><a href="securing-samba.html#id2928559">Upgrading Samba</a></dt><dt><a href="securing-samba.html#id2928583">Common Errors</a></dt><dd><dl><dt><a href="securing-samba.html#id2928602">Smbclient works on localhost, but the network is dead</a></dt><dt><a href="securing-samba.html#id2928626">Why can users access home directories of other users?</a></dt></dl></dd></dl></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2929518"></a>Introduction</h2></div></div><div></div></div><p>
This note was attached to the Samba 2.2.8 release notes as it contained an
important security fix. The information contained here applies to Samba
installations in general.
-</p></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2900517"></a>Using host based protection</h2></div></div><p>
-In many installations of Samba the greatest threat comes for outside
-your immediate network. By default Samba will accept connections from
-any host, which means that if you run an insecure version of Samba on
-a host that is directly connected to the Internet you can be
-especially vulnerable.
</p><p>
-One of the simplest fixes in this case is to use the <b>hosts allow</b> and
-<b>hosts deny</b> options in the Samba <tt>smb.conf</tt> configuration file to only
-allow access to your server from a specific range of hosts. An example
-might be:
-</p><pre class="programlisting">
- hosts allow = 127.0.0.1 192.168.2.0/24 192.168.3.0/24
- hosts deny = 0.0.0.0/0
-</pre><p>
-The above will only allow SMB connections from 'localhost' (your own
-computer) and from the two private networks 192.168.2 and
-192.168.3. All other connections will be refused as soon
-as the client sends its first packet. The refusal will be marked as a
-'not listening on called name' error.
-</p></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2900967"></a>Using interface protection</h2></div></div><p>
-By default Samba will accept connections on any network interface that
-it finds on your system. That means if you have a ISDN line or a PPP
-connection to the Internet then Samba will accept connections on those
-links. This may not be what you want.
-</p><p>
-You can change this behaviour using options like the following:
-</p><pre class="programlisting">
- interfaces = eth* lo
- bind interfaces only = yes
-</pre><p>
-This tells Samba to only listen for connections on interfaces with a
-name starting with 'eth' such as eth0, eth1, plus on the loopback
-interface called 'lo'. The name you will need to use depends on what
-OS you are using, in the above I used the common name for Ethernet
-adapters on Linux.
-</p><p>
-If you use the above and someone tries to make a SMB connection to
-your host over a PPP interface called 'ppp0' then they will get a TCP
-connection refused reply. In that case no Samba code is run at all as
-the operating system has been told not to pass connections from that
-interface to any samba process.
-</p></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2901018"></a>Using a firewall</h2></div></div><p>
-Many people use a firewall to deny access to services that they don't
-want exposed outside their network. This can be a very good idea,
-although I would recommend using it in conjunction with the above
-methods so that you are protected even if your firewall is not active
-for some reason.
+A new apprentice reported for duty to the Chief Engineer of a boiler house. He said, &quot;Here I am,
+if you will show me the boiler I'll start working on it.&quot; Then engineer replied, &quot;You're leaning
+on it!&quot;
</p><p>
-If you are setting up a firewall then you need to know what TCP and
-UDP ports to allow and block. Samba uses the following:
-</p><pre class="programlisting">
- UDP/137 - used by nmbd
- UDP/138 - used by nmbd
- TCP/139 - used by smbd
- TCP/445 - used by smbd
-</pre><p>
-The last one is important as many older firewall setups may not be
-aware of it, given that this port was only added to the protocol in
-recent years.
-</p></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2901061"></a>Using a IPC$ share deny</h2></div></div><p>
-If the above methods are not suitable, then you could also place a
-more specific deny on the IPC$ share that is used in the recently
-discovered security hole. This allows you to offer access to other
-shares while denying access to IPC$ from potentially untrustworthy
-hosts.
+Security concerns are just like that: You need to know a little about the subject to appreciate
+how obvious most of it really is. The challenge for most of us is to discover that first morsel
+of knowledge with which we may unlock the secrets of the masters.
+</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2929550"></a>Features and Benefits</h2></div></div><div></div></div><p>
+There are three level at which security principals must be observed in order to render a site
+at least moderately secure. These are: the perimeter firewall, the configuration of the host
+server that is running Samba, and Samba itself.
</p><p>
-To do that you could use:
-</p><pre class="programlisting">
- [ipc$]
- hosts allow = 192.168.115.0/24 127.0.0.1
- hosts deny = 0.0.0.0/0
-</pre><p>
-this would tell Samba that IPC$ connections are not allowed from
-anywhere but the two listed places (localhost and a local
-subnet). Connections to other shares would still be allowed. As the
-IPC$ share is the only share that is always accessible anonymously
-this provides some level of protection against attackers that do not
-know a username/password for your host.
+Samba permits a most flexible approach to network security. As far as possible Samba implements
+the latest protocols to permit more secure MS Windows file and print operations.
</p><p>
-If you use this method then clients will be given a 'access denied'
-reply when they try to access the IPC$ share. That means that those
-clients will not be able to browse shares, and may also be unable to
-access some other resources.
+Samba may be secured from connections that originate from outside the local network. This may be
+done using <span class="emphasis"><em>host based protection</em></span> (using samba's implementation of a technology
+known as &quot;tcpwrappers&quot;, or it may be done be using <span class="emphasis"><em>interface based exclusion</em></span>
+so that <span class="application">smbd</span> will bind only to specifically permitted interfaces. It is also
+possible to set specific share or resource based exclusions, eg: on the <i class="parameter"><tt>IPC$</tt></i>
+auto-share. The <i class="parameter"><tt>IPC$</tt></i> share is used for browsing purposes as well as to establish
+TCP/IP connections.
</p><p>
-This is not recommended unless you cannot use one of the other
-methods listed above for some reason.
-</p></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2900617"></a>NTLMv2 Security</h2></div></div><p>
-To configure NTLMv2 authentication the following registry keys are worth knowing about:
-</p><p>
-</p><pre class="programlisting">
- [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa]
- &quot;lmcompatibilitylevel&quot;=dword:00000003
+Another method by which Samba may be secured is by way of setting Access Control Entries in an Access
+Control List on the shares themselves. This is discussed in the chapter on File, Directory and Share Access
+Control.
+</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2928211"></a>Technical Discussion of Protective Measures and Issues</h2></div></div><div></div></div><p>
+The key challenge of security is the fact that protective measures suffice at best
+only to close the door on known exploits and breach techniques. Never assume that
+because you have followed these few measures that the Samba server is now an impenetrable
+fortress! Given the history of information systems so far, it is only a matter of time
+before someone will find yet another vulnerability.
+</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928229"></a>Using host based protection</h3></div></div><div></div></div><p>
+ In many installations of Samba the greatest threat comes for outside
+ your immediate network. By default Samba will accept connections from
+ any host, which means that if you run an insecure version of Samba on
+ a host that is directly connected to the Internet you can be
+ especially vulnerable.
+ </p><p>
+ One of the simplest fixes in this case is to use the <i class="parameter"><tt>hosts allow</tt></i> and
+ <i class="parameter"><tt>hosts deny</tt></i> options in the Samba <tt class="filename">smb.conf</tt> configuration file to only
+ allow access to your server from a specific range of hosts. An example
+ might be:
+ </p><pre class="programlisting">
+ hosts allow = 127.0.0.1 192.168.2.0/24 192.168.3.0/24
+ hosts deny = 0.0.0.0/0
+ </pre><p>
+ The above will only allow SMB connections from 'localhost' (your own
+ computer) and from the two private networks 192.168.2 and
+ 192.168.3. All other connections will be refused as soon
+ as the client sends its first packet. The refusal will be marked as a
+ <span class="errorname">not listening on called name</span> error.
+ </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928297"></a>User based protection</h3></div></div><div></div></div><p>
+ If you want to restrict access to your server to valid users only then the following
+ method may be of use. In the <tt class="filename">smb.conf</tt> <i class="parameter"><tt>[globals]</tt></i> section put:
+ </p><pre class="programlisting">
+ valid users = @smbusers, jacko
+ </pre><p>
+ What this does is, it restricts all server access to either the user <span class="emphasis"><em>jacko</em></span>
+ or to members of the system group <span class="emphasis"><em>smbusers</em></span>.
+ </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928349"></a>Using interface protection</h3></div></div><div></div></div><p>
+ By default Samba will accept connections on any network interface that
+ it finds on your system. That means if you have a ISDN line or a PPP
+ connection to the Internet then Samba will accept connections on those
+ links. This may not be what you want.
+ </p><p>
+ You can change this behaviour using options like the following:
+ </p><pre class="programlisting">
+ interfaces = eth* lo
+ bind interfaces only = yes
+ </pre><p>
+ This tells Samba to only listen for connections on interfaces with a
+ name starting with 'eth' such as eth0, eth1, plus on the loopback
+ interface called 'lo'. The name you will need to use depends on what
+ OS you are using, in the above I used the common name for Ethernet
+ adapters on Linux.
+ </p><p>
+ If you use the above and someone tries to make a SMB connection to
+ your host over a PPP interface called 'ppp0' then they will get a TCP
+ connection refused reply. In that case no Samba code is run at all as
+ the operating system has been told not to pass connections from that
+ interface to any samba process.
+ </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928399"></a>Using a firewall</h3></div></div><div></div></div><p>
+ Many people use a firewall to deny access to services that they don't
+ want exposed outside their network. This can be a very good idea,
+ although I would recommend using it in conjunction with the above
+ methods so that you are protected even if your firewall is not active
+ for some reason.
+ </p><p>
+ If you are setting up a firewall then you need to know what TCP and
+ UDP ports to allow and block. Samba uses the following:
+ </p><table class="simplelist" border="0" summary="Simple list"><tr><td>UDP/137 - used by nmbd</td></tr><tr><td>UDP/138 - used by nmbd</td></tr><tr><td>TCP/139 - used by smbd</td></tr><tr><td>TCP/445 - used by smbd</td></tr></table><p>
+ The last one is important as many older firewall setups may not be
+ aware of it, given that this port was only added to the protocol in
+ recent years.
+ </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928455"></a>Using a IPC$ share deny</h3></div></div><div></div></div><p>
+ If the above methods are not suitable, then you could also place a
+ more specific deny on the IPC$ share that is used in the recently
+ discovered security hole. This allows you to offer access to other
+ shares while denying access to IPC$ from potentially untrustworthy
+ hosts.
+ </p><p>
+ To do that you could use:
+ </p><pre class="programlisting">
+[ipc$]
+ hosts allow = 192.168.115.0/24 127.0.0.1
+ hosts deny = 0.0.0.0/0
+ </pre><p>
+ this would tell Samba that IPC$ connections are not allowed from
+ anywhere but the two listed places (localhost and a local
+ subnet). Connections to other shares would still be allowed. As the
+ IPC$ share is the only share that is always accessible anonymously
+ this provides some level of protection against attackers that do not
+ know a username/password for your host.
+ </p><p>
+ If you use this method then clients will be given a <span class="errorname">access denied</span>
+ reply when they try to access the IPC$ share. That means that those
+ clients will not be able to browse shares, and may also be unable to
+ access some other resources.
+ </p><p>
+ This is not recommended unless you cannot use one of the other
+ methods listed above for some reason.
+ </p></div><div xmlns:ns41="" class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928521"></a>NTLMv2 Security</h3></div></div><div></div></div><p>
+ To configure NTLMv2 authentication the following registry keys are worth knowing about:
+ </p><ns41:p>
+ </ns41:p><pre class="screen">
+ [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa]
+ &quot;lmcompatibilitylevel&quot;=dword:00000003
- 0x3 - Send NTLMv2 response only. Clients will use NTLMv2 authentication,
- use NTLMv2 session security if the server supports it. Domain
- controllers accept LM, NTLM and NTLMv2 authentication.
+ 0x3 - Send NTLMv2 response only. Clients will use NTLMv2 authentication,
+ use NTLMv2 session security if the server supports it. Domain
+ controllers accept LM, NTLM and NTLMv2 authentication.
- [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0]
- &quot;NtlmMinClientSec&quot;=dword:00080000
+ [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0]
+ &quot;NtlmMinClientSec&quot;=dword:00080000
- 0x80000 - NTLMv2 session security. If either NtlmMinClientSec or
- NtlmMinServerSec is set to 0x80000, the connection will fail if NTLMv2
- session security is not negotiated.
-</pre><p>
-</p></div><div class="sect1" lang="en"><div class="titlepage"><div><h2 class="title" style="clear: both"><a name="id2900653"></a>Upgrading Samba</h2></div></div><p>
+ 0x80000 - NTLMv2 session security. If either NtlmMinClientSec or
+ NtlmMinServerSec is set to 0x80000, the connection will fail if NTLMv2
+ session security is not negotiated.
+ </pre><ns41:p>
+ </ns41:p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2928559"></a>Upgrading Samba</h2></div></div><div></div></div><p>
Please check regularly on <a href="http://www.samba.org/" target="_top">http://www.samba.org/</a> for updates and
important announcements. Occasionally security releases are made and
it is highly recommended to upgrade Samba when a security vulnerability
is discovered.
-</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="integrate-ms-networks.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="optional.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="unicode.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 23. Integrating MS Windows networks with Samba </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 25. Unicode/Charsets</td></tr></table></div></body></html>
+</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2928583"></a>Common Errors</h2></div></div><div></div></div><p>
+If all of samba and host platform configuration were really as intuitive as one might like then this
+section would not be necessary. Security issues are often vexing for a support person to resolve, not
+because of the complexity of the problem, but for reason that most admininstrators who post what turns
+out to be a security problem request are totally convinced that the problem is with Samba.
+</p><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928602"></a>Smbclient works on localhost, but the network is dead</h3></div></div><div></div></div><p>
+ This is a very common problem. Red Hat Linux (as do others) will install a default firewall.
+ With the default firewall in place only traffic on the loopback adapter (IP address 127.0.0.1)
+ will be allowed through the firewall.
+ </p><p>
+ The solution is either to remove the firewall (stop it) or to modify the firewall script to
+ allow SMB networking traffic through. See section above in this chapter.
+ </p></div><div xmlns:ns42="" class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928626"></a>Why can users access home directories of other users?</h3></div></div><div></div></div><p>
+ &#8220;<span class="quote">
+ We are unable to keep individual users from mapping to any other user's
+ home directory once they have supplied a valid password! They only need
+ to enter their own password. I have not found *any* method that I can
+ use to configure samba to enforce that only a user may map their own
+ home directory.
+ </span>&#8221;
+ </p><p>&#8220;<span class="quote">
+ User xyzzy can map his home directory. Once mapped user xyzzy can also map
+ *anyone* elses home directory!
+ </span>&#8221;</p><p>
+ This is not a security flaw, it is by design. Samba allows
+ users to have *exactly* the same access to the UNIX filesystem
+ as they would if they were logged onto the UNIX box, except
+ that it only allows such views onto the file system as are
+ allowed by the defined shares.
+ </p><p>
+ This means that if your UNIX home directories are set up
+ such that one user can happily cd into another users
+ directory and do an ls, the UNIX security solution is to
+ change the UNIX file permissions on the users home directories
+ such that the cd and ls would be denied.
+ </p><p>
+ Samba tries very hard not to second guess the UNIX administrators
+ security policies, and trusts the UNIX admin to set
+ the policies and permissions he or she desires.
+ </p><p>
+ Samba does allow the setup you require when you have set the
+ <i class="parameter"><tt>only user = yes</tt></i> option on the share, is that you have not set the
+ valid users list for the share.
+ </p><ns42:p>
+ Note that only user works in conjunction with the users= list,
+ so to get the behavior you require, add the line :
+ </ns42:p><pre class="programlisting">
+ users = %S
+ </pre><ns42:p>
+ this is equivalent to:
+ </ns42:p><pre class="programlisting">
+ valid users = %S
+ </pre><ns42:p>
+ to the definition of the <i class="parameter"><tt>[homes]</tt></i> share, as recommended in
+ the <tt class="filename">smb.conf</tt> man page.
+ </ns42:p></div></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="locking.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="optional.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="InterdomainTrusts.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter 14. File and Record Locking </td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 16. Interdomain Trust Relationships</td></tr></table></div></body></html>