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diff --git a/docs/htmldocs/Samba3-HOWTO/securing-samba.html b/docs/htmldocs/Samba3-HOWTO/securing-samba.html new file mode 100644 index 0000000000..cdfeb0f287 --- /dev/null +++ b/docs/htmldocs/Samba3-HOWTO/securing-samba.html @@ -0,0 +1,263 @@ +<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 V1.71.0"><link rel="start" href="index.html" title="The Official Samba-3 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="surname">Tridgell</span></h3><div class="affiliation"><span class="orgname">Samba Team<br></span><div class="address"><p><code class="email"><<a 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 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#id379562">Introduction</a></span></dt><dt><span class="sect1"><a href="securing-samba.html#id379650">Features and Benefits</a></span></dt><dt><span class="sect1"><a href="securing-samba.html#id379785">Technical Discussion of Protective Measures and Issues</a></span></dt><dd><dl><dt><span class="sect2"><a href="securing-samba.html#id379797">Using Host-Based Protection</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id379935">User-Based Protection</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id379993">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#id380322">Using IPC$ Share-Based Denials </a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id380458">NTLMv2 Security</a></span></dt></dl></dd><dt><span class="sect1"><a href="securing-samba.html#id380506">Upgrading Samba</a></span></dt><dt><span class="sect1"><a href="securing-samba.html#id380547">Common Errors</a></span></dt><dd><dl><dt><span class="sect2"><a href="securing-samba.html#id380559">Smbclient Works on Localhost, but the Network Is Dead</a></span></dt><dt><span class="sect2"><a href="securing-samba.html#id380583">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="id379562"></a>Introduction</h2></div></div></div><p> +<a class="indexterm" name="id379570"></a> +<a class="indexterm" name="id379577"></a> +<a class="indexterm" name="id379584"></a> +<a class="indexterm" name="id379590"></a> +<a class="indexterm" name="id379597"></a> +<a class="indexterm" name="id379604"></a> +<a class="indexterm" name="id379611"></a> +The information contained in this chapter applies in general to all Samba installations. Security is +everyone's concern in the information technology world. A surprising number of Samba servers are being +installed on machines that have direct internet access, thus security is made more critical than it would have been had the +server been located behind a firewall and on a private network. Paranoia regarding server security is causing +some network administrators to insist on the installation of robust firewalls even on servers that are located +inside secured networks. This chapter provides information to assist the administrator who understands +how to create the needed barriers and deterents against “<span class="quote">the enemy</span>”, no matter where [s]he may +come from. +</p><div class="blockquote"><blockquote class="blockquote"><p> +A new apprentice reported for duty to the chief engineer of a boiler house. He said, “<span class="quote">Here I am, +if you will show me the boiler I'll start working on it.</span>” Then engineer replied, “<span class="quote">You're leaning +on it!</span>” +</p></blockquote></div><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="id379650"></a>Features and Benefits</h2></div></div></div><p> +<a class="indexterm" name="id379658"></a> +<a class="indexterm" name="id379665"></a> +<a class="indexterm" name="id379671"></a> +<a class="indexterm" name="id379678"></a> +There are three levels at which security principles must be observed in order to render a site +at least moderately secure. They 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> +<a class="indexterm" name="id379695"></a> +<a class="indexterm" name="id379702"></a> +<a class="indexterm" name="id379709"></a> +Samba can be secured from connections that originate from outside the local network. This can be done using +<span class="emphasis"><em>host-based protection</em></span>, using Samba's implementation of a technology known as +“<span class="quote">tcpwrappers,</span>” or it may be done be using <span class="emphasis"><em>interface-based exclusion</em></span> so +<span class="application">smbd</span> will bind only to specifically permitted interfaces. It is also possible to set specific share- or +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. +</p><p> +<a class="indexterm" name="id379752"></a> +<a class="indexterm" name="id379760"></a> +<a class="indexterm" name="id379767"></a> +Another method by which Samba may be secured is by setting Access Control Entries (ACEs) in an Access +Control List (ACL) on the shares themselves. This is discussed in +<a href="AccessControls.html" title="Chapter 16. File, Directory, and Share Access Controls">File, Directory, and Share Access Controls</a>. +</p></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id379785"></a>Technical Discussion of Protective Measures and Issues</h2></div></div></div><p> +The key challenge of security is 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, 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="id379797"></a>Using Host-Based Protection</h3></div></div></div><p> +<a class="indexterm" name="id379805"></a> +<a class="indexterm" name="id379812"></a> +<a class="indexterm" name="id379818"></a> + In many installations of Samba, the greatest threat comes from outside + your immediate network. By default, Samba accepts 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> +<a class="indexterm" name="id379831"></a> +<a class="indexterm" name="id379838"></a> + One of the simplest fixes in this case is to use the <a class="indexterm" name="id379845"></a>hosts allow and + <a class="indexterm" name="id379852"></a>hosts deny options in the Samba <code class="filename">smb.conf</code> configuration file to + allow access to your server only from a specific range of hosts. An example might be: + </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id379872"></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="id379884"></a><em class="parameter"><code>hosts deny = 0.0.0.0/0</code></em></td></tr></table><p> + </p><p> +<a class="indexterm" name="id379900"></a> +<a class="indexterm" name="id379907"></a> +<a class="indexterm" name="id379914"></a> + The above will allow SMB connections only from <code class="constant">localhost</code> (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 <code class="literal">not listening on called name</code> error. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id379935"></a>User-Based Protection</h3></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 <code class="filename">smb.conf</code> <em class="parameter"><code>[global]</code></em> section put: + </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id379961"></a><em class="parameter"><code>valid users = @smbusers, jacko</code></em></td></tr></table><p> + </p><p> +<a class="indexterm" name="id379976"></a> + This restricts all server access either to 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="id379993"></a>Using Interface Protection</h3></div></div></div><p> +<a class="indexterm" name="id380001"></a> +<a class="indexterm" name="id380008"></a> +<a class="indexterm" name="id380015"></a> + By default, Samba accepts connections on any network interface that + it finds on your system. That means if you have an 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 behavior using options like this: + </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id380033"></a><em class="parameter"><code>interfaces = eth* lo</code></em></td></tr><tr><td><a class="indexterm" name="id380046"></a><em class="parameter"><code>bind interfaces only = yes</code></em></td></tr></table><p> + </p><p> +<a class="indexterm" name="id380062"></a> +<a class="indexterm" name="id380068"></a> +<a class="indexterm" name="id380075"></a> +<a class="indexterm" name="id380082"></a> + This tells Samba to listen for connections only on interfaces with a name starting with + <code class="constant">eth</code> such as <code class="constant">eth0</code> or <code class="constant">eth1</code>, plus on the loopback interface called + <code class="constant">lo</code>. 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> +<a class="indexterm" name="id380109"></a> +<a class="indexterm" name="id380116"></a> +<a class="indexterm" name="id380122"></a> +<a class="indexterm" name="id380129"></a> + If you use the above and someone tries to make an SMB connection to your host over a PPP interface called + <code class="constant">ppp0</code>, then [s]he will get a TCP connection refused reply. In that case, no Samba code + is run at all, because the operating system has been told not to pass connections from that interface to any + Samba process. However, the refusal helps a would-be cracker by confirming that the IP address provides + valid active services. + </p><p> +<a class="indexterm" name="id380146"></a> +<a class="indexterm" name="id380153"></a> +<a class="indexterm" name="id380160"></a> +<a class="indexterm" name="id380167"></a> +<a class="indexterm" name="id380174"></a> + A better response would be to ignore the connection (from, for example, ppp0) altogether. The + advantage of ignoring the connection attempt, as compared with refusing it, is that it foils those who + probe an interface with the sole intention of finding valid IP addresses for later use in exploitation + or denial of service attacks. This method of dealing with potential malicious activity demands the + use of appropriate firewall mechanisms. + </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> +<a class="indexterm" name="id380198"></a> +<a class="indexterm" name="id380205"></a> +<a class="indexterm" name="id380212"></a> + Many people use a firewall to deny access to services they do not want exposed outside their network. This can + be a good idea, although I recommend using it in conjunction with the above methods so you are protected even + if your firewall is not active for some reason. + </p><p> + If you are setting up a firewall, you need to know what TCP and UDP ports to allow and block. Samba uses + the following: +<a class="indexterm" name="id380225"></a> +<a class="indexterm" name="id380232"></a> +<a class="indexterm" name="id380239"></a> +<a class="indexterm" name="id380246"></a> +<a class="indexterm" name="id380252"></a> + </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> +<a class="indexterm" name="id380286"></a> + The last one is important because many older firewall setups may not be aware of it, given that this port + was only added to the protocol in recent years. + </p><p> +<a class="indexterm" name="id380297"></a> +<a class="indexterm" name="id380304"></a> +<a class="indexterm" name="id380311"></a> + When configuring a firewall, the high order ports (1024-65535) are often used for outgoing connections and + therefore should be permitted through the firewall. It is prudent to block incoming packets on the high order + ports except for established connections. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id380322"></a>Using IPC$ Share-Based Denials </h3></div></div></div><p> +<a class="indexterm" name="id380330"></a> +<a class="indexterm" name="id380337"></a> +<a class="indexterm" name="id380344"></a> + 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 this you could use: + </p><table class="simplelist" border="0" summary="Simple list"><tr><td> </td></tr><tr><td><em class="parameter"><code>[IPC$]</code></em></td></tr><tr><td><a class="indexterm" name="id380371"></a><em class="parameter"><code>hosts allow = 192.168.115.0/24 127.0.0.1</code></em></td></tr><tr><td><a class="indexterm" name="id380384"></a><em class="parameter"><code>hosts deny = 0.0.0.0/0</code></em></td></tr></table><p> + </p><p> +<a class="indexterm" name="id380399"></a> +<a class="indexterm" name="id380406"></a> +<a class="indexterm" name="id380413"></a> + This instructs Samba that IPC$ connections are not allowed from anywhere except the two listed network + addresses (localhost and the 192.168.115 subnet). Connections to other shares are still allowed. Because the + IPC$ share is the only share that is always accessible anonymously, this provides some level of protection + against attackers who do not know a valid username/password for your host. + </p><p> +<a class="indexterm" name="id380427"></a> +<a class="indexterm" name="id380433"></a> +<a class="indexterm" name="id380440"></a> + If you use this method, then clients will be given an <code class="literal">`access denied'</code> reply when they try + to access the IPC$ share. Those clients will not be able to browse shares and may also be unable to access + some other resources. This is not recommended unless for some reason you cannot use one of the other methods + just discussed. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id380458"></a>NTLMv2 Security</h3></div></div></div><p> +<a class="indexterm" name="id380466"></a> + 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> + The value 0x00000003 means to 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> + The value 0x00080000 means permit only NTLMv2 session security. If either NtlmMinClientSec or + NtlmMinServerSec is set to 0x00080000, the connection will fail if NTLMv2 + session security is negotiated. + </p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id380506"></a>Upgrading Samba</h2></div></div></div><p> +<a class="indexterm" name="id380514"></a> +<a class="indexterm" name="id380521"></a> +<a class="indexterm" name="id380527"></a> +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 promptly 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="id380547"></a>Common Errors</h2></div></div></div><p> +If all Samba and host platform configurations were really as intuitive as one might like them to be, this +chapter would not be necessary. Security issues are often vexing for a support person to resolve, not because +of the complexity of the problem, but because 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="id380559"></a>Smbclient Works on Localhost, but the Network Is Dead</h3></div></div></div><p> + This is a common problem. Linux vendors tend to install a default firewall. + With the default firewall in place, only traffic on the loopback adapter (IP address 127.0.0.1) + is allowed through the firewall. + </p><p> + The solution is either to remove the firewall (stop it) or modify the firewall script to + allow SMB networking traffic through. See <a href="securing-samba.html#firewallports" title="Using a Firewall">the Using a + Firewall</a> section. + </p></div><div class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id380583"></a>Why Can Users Access Other Users' Home Directories?</h3></div></div></div><p> + “<span class="quote"> +<a class="indexterm" name="id380593"></a> +<a class="indexterm" name="id380600"></a> + 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 to + configure Samba so that users may map only 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> +<a class="indexterm" name="id380619"></a> +<a class="indexterm" name="id380626"></a> + This is not a security flaw, it is by design. Samba allows users to have exactly the same access to the UNIX + file system as when they were logged on to the UNIX box, except that it only allows such views onto the file + system as are allowed by the defined shares. + </p><p> +<a class="indexterm" name="id380638"></a> +<a class="indexterm" name="id380645"></a> + If your UNIX home directories are set up so that one user can happily <code class="literal">cd</code> + into another user's directory and execute <code class="literal">ls</code>, the UNIX security solution is to change file + permissions on the user's home directories so that the <code class="literal">cd</code> and <code class="literal">ls</code> are denied. + </p><p> +<a class="indexterm" name="id380680"></a> +<a class="indexterm" name="id380687"></a> + Samba tries very hard not to second guess the UNIX administrator's security policies and + trusts the UNIX admin to set the policies and permissions he or she desires. + </p><p> + Samba allows the behavior you require. Simply put the <a class="indexterm" name="id380699"></a>only user = %S + option in the <em class="parameter"><code>[homes]</code></em> share definition. + </p><p> + The <a class="indexterm" name="id380716"></a>only user works in conjunction with the <a class="indexterm" name="id380723"></a>users = list, + so to get the behavior you require, add the line: + </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id380736"></a><em class="parameter"><code>users = %S</code></em></td></tr></table><p> + This is equivalent to adding + </p><table class="simplelist" border="0" summary="Simple list"><tr><td><a class="indexterm" name="id380754"></a><em class="parameter"><code>valid users = %S</code></em></td></tr></table><p> + to the definition of the <em class="parameter"><code>[homes]</code></em> share, as recommended in + the <code class="filename">smb.conf</code> 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 17. 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