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| author | Jelmer Vernooij <jelmer@samba.org> | 2003-08-15 18:26:34 +0000 |
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| committer | Jelmer Vernooij <jelmer@samba.org> | 2003-08-15 18:26:34 +0000 |
| commit | d069dacb6e17866dd5d3862e1837a9cae008644f (patch) | |
| tree | c1b660005d31583819c7f43f79168a3332150a85 /docs/htmldocs/securing-samba.html | |
| parent | cedd66b6e67f4c463eaa072f0e6d87ee1f55718e (diff) | |
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diff --git a/docs/htmldocs/securing-samba.html b/docs/htmldocs/securing-samba.html new file mode 100644 index 0000000000..492780765e --- /dev/null +++ b/docs/htmldocs/securing-samba.html @@ -0,0 +1,192 @@ +<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="samba-doc.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"><<a href="mailto:tridge@samba.org">tridge@samba.org</a>></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"><<a href="mailto:jht@samba.org">jht@samba.org</a>></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#id2910685">Introduction</a></dt><dt><a href="securing-samba.html#id2910722">Features and Benefits</a></dt><dt><a href="securing-samba.html#id2910796">Technical Discussion of Protective Measures and Issues</a></dt><dd><dl><dt><a href="securing-samba.html#id2910816">Using host based protection</a></dt><dt><a href="securing-samba.html#id2910915">User based protection</a></dt><dt><a href="securing-samba.html#id2910975">Using interface protection</a></dt><dt><a href="securing-samba.html#id2911042">Using a firewall</a></dt><dt><a href="securing-samba.html#id2911098">Using a IPC$ share deny</a></dt><dt><a href="securing-samba.html#id2911187">NTLMv2 Security</a></dt></dl></dd><dt><a href="securing-samba.html#id2911245">Upgrading Samba</a></dt><dt><a href="securing-samba.html#id2911271">Common Errors</a></dt><dd><dl><dt><a href="securing-samba.html#id2911289">Smbclient works on localhost, but the network is dead</a></dt><dt><a href="securing-samba.html#id2911314">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="id2910685"></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><p> +A new apprentice reported for duty to the Chief Engineer of a boiler house. He said, "Here I am, +if you will show me the boiler I'll start working on it." Then engineer replied, "You're leaning +on it!" +</p><p> +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="id2910722"></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> +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> +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 "tcpwrappers", 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> +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="id2910796"></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="id2910816"></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 <a class="indexterm" name="id2910838"></a><i class="parameter"><tt>hosts allow</tt></i> and + <a class="indexterm" name="id2910852"></a><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><table class="simplelist" border="0" summary="Simple list"><tr><td><i class="parameter"><tt>hosts allow = 127.0.0.1 192.168.2.0/24 192.168.3.0/24</tt></i></td></tr><tr><td><i class="parameter"><tt>hosts deny = 0.0.0.0/0</tt></i></td></tr></table><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="id2910915"></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>[global]</tt></i> section put: + </p><table class="simplelist" border="0" summary="Simple list"><tr><td><i class="parameter"><tt>valid users = @smbusers, jacko</tt></i></td></tr></table><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="id2910975"></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><table class="simplelist" border="0" summary="Simple list"><tr><td><i class="parameter"><tt>interfaces = eth* lo</tt></i></td></tr><tr><td><i class="parameter"><tt>bind interfaces only = yes</tt></i></td></tr></table><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="id2911042"></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="id2911098"></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><table class="simplelist" border="0" summary="Simple list"><tr><td> </td></tr><tr><td><i class="parameter"><tt>[ipc$]</tt></i></td></tr><tr><td><i class="parameter"><tt>hosts allow = 192.168.115.0/24 127.0.0.1</tt></i></td></tr><tr><td><i class="parameter"><tt>hosts deny = 0.0.0.0/0</tt></i></td></tr></table><p> + this would tell Samba that IPC$ 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 class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2911187"></a>NTLMv2 Security</h3></div></div><div></div></div><p> + To configure NTLMv2 authentication the following registry keys are worth knowing about: + </p><p> + </p><pre class="screen"> + [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa] + "lmcompatibilitylevel"=dword:00000003 + </pre><p> + </p><p> + 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. + </p><p> + </p><pre class="screen"> + [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0] + "NtlmMinClientSec"=dword:00080000 + </pre><p> + </p><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. + </p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2911245"></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. Check with your OS vendor for OS specific upgrades. +</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2911271"></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 administrators 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="id2911289"></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 class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2911314"></a>Why can users access home directories of other users?</h3></div></div><div></div></div><p> + “<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>” + </p><p>“<span class="quote"> + User xyzzy can map his home directory. Once mapped user xyzzy can also map + *anyone* else's home directory! + </span>”</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 + <a class="indexterm" name="id2911373"></a><i class="parameter"><tt>only user</tt></i> = yes option on the share, is that you have not set the + valid users list for the share. + </p><p> + Note that only user works in conjunction with the users= list, + so to get the behavior you require, add the line : + </p><table class="simplelist" border="0" summary="Simple list"><tr><td><i class="parameter"><tt>users = %S</tt></i></td></tr></table><p> + this is equivalent to: + </p><table class="simplelist" border="0" summary="Simple list"><tr><td><i class="parameter"><tt>valid users = %S</tt></i></td></tr></table><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. + </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="samba-doc.html">Home</a></td><td width="40%" align="right" valign="top"> Chapter 16. Interdomain Trust Relationships</td></tr></table></div></body></html> |