SAMBA Project Documentation
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Chapter 20. Securing Samba

20.1. Introduction

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.

20.2. Using host based protection

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.

One of the simplest fixes in this case is to use the 'hosts allow' and +'hosts deny' options in the Samba smb.conf configuration file to only +allow access to your server from a specific range of hosts. An example +might be:

  hosts allow = 127.0.0.1 192.168.2.0/24 192.168.3.0/24
+  hosts deny = 0.0.0.0/0

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 connections as soon +as the client sends its first packet. The refusal will be marked as a +'not listening on called name' error.

20.3. Using interface protection

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.

You can change this behaviour using options like the following:

  interfaces = eth* lo
+  bind interfaces only = yes

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.

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 process.

20.4. Using a firewall

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.

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:

UDP/137    - used by nmbd
+UDP/138    - used by nmbd
+TCP/139    - used by smbd
+TCP/445    - used by smbd

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.

20.5. Using a IPC$ share deny

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.

To do that you could use:

  [ipc$]
+     hosts allow = 192.168.115.0/24 127.0.0.1
+     hosts deny = 0.0.0.0/0

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.

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.

This is not recommended unless you cannot use one of the other +methods listed above for some reason.

20.6. Upgrading Samba

Please check regularly on http://www.samba.org/ for updates and +important announcements. Occasionally security releases are made and +it is highly recommended to upgrade Samba when a security vulnerability +is discovered.

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