SUMMARY

After time, information is the second most powerful tool available to the malicious computer hacker. Fortunately, it can also be used by the good guys to lock things down. Of course, we've touched on only a handful of the most common applications, because time and space prevent us from covering the limitless diversity of network software that exists. However, using the basic concepts outlined here, you should at least have a start on sealing the lips of the loose-talking software on your network, including:

• Fundamental OS architectures The Windows NT Family's SMB underpinnings make it extremely easy to elicit user credentials, file system exports, and application info . Lock down NT and its progeny by disabling or restricting access to TCP 139 and 445 and setting RestrictAnonymous (or the new, related Network Access settings in Windows XP/Server 2003) as suggested earlier in this chapter. Also, remember that newer Windows OSs haven't totally vanquished these problems, either, and they come with a few new attack points in Active Directory, such as LDAP and DNS. Novell NetWare will divulge similar information that requires due diligence to keep private.

• SNMP Designed to yield as much information as possible to enterprise management suites, improperly configured SNMP agents that use default community strings such as "public" can give out this data to unauthorized users.

• Leaky OS services Finger and rpcbind are good examples of programs that give away too much information. Additionally, most built-in OS services eagerly present banners containing the version number and vendor at the slightest tickle . Disable programs such as finger, use secure implementations of RPC or TCP Wrappers, and find out from vendors how to turn off those darn banners!

• Custom applications Although we haven't discussed it much in this chapter, the rise of built- from-scratch web applications has resulted in a concomitant rise in the information given out by poorly conceived customized app code. Test your own apps, audit their design and implementation, and keep up to date with the newest web app hacks in Hacking Exposed: Web Applications , (McGrawHill/Osborne, 2002).

• Firewalls Many of the sources of these leaks can be screened at the firewall. This isn't an excuse for not patching the holes directly on the machine in question, but it goes a long way toward reducing the risk of exploitation.

Finally, be sure to audit yourself. Wondering what ports are open for enumeration on your machines? There are plenty of Internet sites that will scan your systems remotely. One free one we like to use is located at http://www.linux-sec.net/Audit/nmap.test.gwif.html, which will run a simple nmap scan of a single system or a Class C- sized network (the system requesting the scan must be within this range). For a list of ports and what they are, see http://www.iana.org/assignments/port- numbers .