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| author | Jelmer Vernooij <jelmer@samba.org> | 2003-08-13 06:07:10 +0000 |
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| committer | Jelmer Vernooij <jelmer@samba.org> | 2003-08-13 06:07:10 +0000 |
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diff --git a/docs/htmldocs/securing-samba.html b/docs/htmldocs/securing-samba.html deleted file mode 100644 index bdbc2ae0b5..0000000000 --- a/docs/htmldocs/securing-samba.html +++ /dev/null @@ -1,207 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> -<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"><<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#id2929879">Introduction</a></dt><dt><a href="securing-samba.html#id2929912">Features and Benefits</a></dt><dt><a href="securing-samba.html#id2928572">Technical Discussion of Protective Measures and Issues</a></dt><dd><dl><dt><a href="securing-samba.html#id2928590">Using host based protection</a></dt><dt><a href="securing-samba.html#id2928659">User based protection</a></dt><dt><a href="securing-samba.html#id2928710">Using interface protection</a></dt><dt><a href="securing-samba.html#id2928760">Using a firewall</a></dt><dt><a href="securing-samba.html#id2928816">Using a IPC$ share deny</a></dt><dt><a href="securing-samba.html#id2928881">NTLMv2 Security</a></dt></dl></dd><dt><a href="securing-samba.html#id2928920">Upgrading Samba</a></dt><dt><a href="securing-samba.html#id2928943">Common Errors</a></dt><dd><dl><dt><a href="securing-samba.html#id2928962">Smbclient works on localhost, but the network is dead</a></dt><dt><a href="securing-samba.html#id2928987">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="id2929879"></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="id2929912"></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="id2928572"></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="id2928590"></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="id2928659"></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="id2928710"></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="id2928760"></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="id2928816"></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:ns42="" class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928881"></a>NTLMv2 Security</h3></div></div><div></div></div><p> - To configure NTLMv2 authentication the following registry keys are worth knowing about: - </p><ns42:p> - </ns42:p><pre class="screen"> - [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa] - "lmcompatibilitylevel"=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. - - [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Lsa\MSV1_0] - "NtlmMinClientSec"=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><ns42:p> - </ns42:p></div></div><div class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2928920"></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 class="sect1" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="id2928943"></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="id2928962"></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:ns43="" class="sect2" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="id2928987"></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 - <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><ns43:p> - Note that only user works in conjunction with the users= list, - so to get the behavior you require, add the line : - </ns43:p><pre class="programlisting"> - users = %S - </pre><ns43:p> - this is equivalent to: - </ns43:p><pre class="programlisting"> - valid users = %S - </pre><ns43: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. - </ns43: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. 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