Securing servers
Eventually we'll need sections or subarticles on various different security contexts:
Contents |
First Impressions Are Everything
Login banners are useful sometimes, but since you'll likely already know what system you're logging into and what you're going to be using it for, will probably be unnecessary, and any extraneous information that they give when you login will usually be worthless to you but potentially useful to an attacker. If you want to change it (or remove it,) you'll need to:
1. edit /etc/motd (make it blank or put in a warning like "you're being logged" or "authorized access ONLY" or something 2. touch /etc/COPYRIGHT and 3. add update_motd="NO" to /etc/rc.conf. 4. reboot to verify that the changes are made and effective.
Security in a local user context
things needed here:(cover common gotchas and SNAFUs concerning local security; ie preventing valid shell users from obtaining privileges they aren't supposed to have or doing damage they shouldn't be able to do. sudo is clearly a must with this one, as is some discussion of running daemons under special user accounts, and the dangers of overusing "nobody" to run daemons. a quick rundown of system files that permissions should be double-checked on, like /etc/passwd, /etc/master.passwd, /etc/group, and the databases associated with them should also be covered.)
Security in an internet context: what's listening?
We'll want to know what ports are open and listening. If you didn't follow the installation instructions and installed IPv6 support when you installed the system (like me), you'll want to check for IPv6 sockets as well as IPv4; become root and run sockstat with -46 as an argument; this will let you know the socket status for both IPv4 and IPv6 sockets (in this context, a socket = port + protocol). For more details, see the sockstat entry's section on security.
Authentication, Encryption and You
FreeBSD encrypts passwords. Unfortunately, it doesn't do it the strongest way possible by default. The reason being that stronger encryption takes more effort to perform and can sometimes be slow. But if you're serious about making your machine harder to crack, you'll want to switch your password encryption from md5 to the blowfish algorithm. Blowfish has the benefit of being both fast and strong (military-grade strong.) This is a 4-step process. 1. edit /etc/login.conf and change the passwd_format entry to
:passwd_format=blf:\
2. rebuild the login.conf database with
samizdata# cap_mkdb /etc/login.conf
3. change all your user's passwords (or get them to change 'em by expiring their passwords) by running passwd for everyone (INCLUDING ROOT):
samizdata# passwd
4. you'll want to change the configuration file that the adduser program calls to use blowfish automagically. Do this by changing the crypt_default=md5 line in /etc/auth.conf to crypt_default=blf so that any new accounts you make on the system use it from the get-go.
Security in a local area network context
(probably the shortest of the categories - specific things to watch for in an un-firewalled and extremely-high-bandwidth mostly-trusted environment.)
Security through better logging
(keeping time up to date with ntpd or regularly scheduled ntpdate - and it's worth noting that I've NEVER personally been able to get ntpd to actually update the damn system time, all it seems to do is maintain a drift file for me - but anyway, importance of keeping system time precise down to milliseconds for coordination of system logs with logs at ISPs and other servers involved in network attacks, use of tripwire or built-in daily root emails to monitor for changes in important system files, and also the benefits of either maintaining a separate log server or REGULARLY moving logs off-system to a machine that doesn't trust the server it's getting the logs from one damn bit. this topic may actually need to be moved to its own separate subarticle.)
Of course, each of these sections can themselves spawn entire new subsections / subarticles of their own. There's a reason entire books have been published on computer security! =)
Try to remember, when writing these articles, that "short and sweet" is best, when it comes to a single article. If at all possible, try to limit the scope of any given article to a page or two of text; if you need to refer to something that is going to run a few pages all by itself, consider writing a separate article for that topic and hyperlinking it for people who need it. For example, obviously firewalls need discussion in any internet-context security article, but instead of trying to go over setting one up in the midst of the internet security article itself, it's better to write one article about firewalls and another about the big picture, and just link them.
