MacOS – Do firewall tools exist for OS X Mavericks for preventing brute force attacks

firewallmacosSecurity

Here's the deal:

Over the last few weeks, I've noticed a large number of authentication failures for both the sshd service and the screensharingd service on my Mac OS X Mavericks server (running 10.9.2 (Build 13C64), Server v3.1.1 (Build 13S4140), Apache v2.2.26, and OpenSSL v1.0.1g (no Heartbleed for me, haha)). A quick sample of some server logs:

Apr 21 08:08:45 [myhost] sshd[6558]: Invalid user fls from 83.222.230.90
Apr 21 08:08:45 [myhost] sshd[6558]: input_userauth_request: invalid user fls [preauth]
Apr 21 08:08:45 [myhost] sshd[6558]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]
Apr 21 08:08:47 [myhost] sshd[6560]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]
Apr 21 08:08:48 [myhost] sshd[6568]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]
Apr 21 08:08:49 [myhost] sshd[6571]: Invalid user x from 83.222.230.90
Apr 21 08:08:49 [myhost] sshd[6571]: input_userauth_request: invalid user x [preauth]
Apr 21 08:08:50 [myhost] sshd[6571]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]
Apr 21 08:08:51 [myhost] sshd[6573]: Invalid user http from 83.222.230.90
Apr 21 08:08:51 [myhost] sshd[6573]: input_userauth_request: invalid user http [preauth]
Apr 21 08:08:51 [myhost] sshd[6573]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]
Apr 21 08:08:52 [myhost] sshd[6578]: Invalid user mp3 from 83.222.230.90
Apr 21 08:08:52 [myhost] sshd[6578]: input_userauth_request: invalid user mp3 [preauth]
Apr 21 08:08:53 [myhost] sshd[6578]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]
Apr 21 08:08:54 [myhost] sshd[6581]: Invalid user oracle from 83.222.230.90
Apr 21 08:08:54 [myhost] sshd[6581]: input_userauth_request: invalid user oracle [preauth]
Apr 21 08:08:54 [myhost] sshd[6581]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]
Apr 21 08:08:55 [myhost] sshd[6584]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]
Apr 21 08:08:57 [myhost] sshd[6589]: Invalid user r00t from 83.222.230.90
Apr 21 08:08:57 [myhost] sshd[6589]: input_userauth_request: invalid user r00t [preauth]
Apr 21 08:08:57 [myhost] sshd[6589]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]
Apr 21 08:08:58 [myhost] sshd[6595]: Invalid user bin from 83.222.230.90
Apr 21 08:08:58 [myhost] sshd[6595]: input_userauth_request: invalid user bin [preauth]
Apr 21 08:08:59 [myhost] sshd[6595]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]
Apr 21 08:09:00 [myhost] sshd[6597]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]
Apr 21 08:09:01 [myhost] sshd[6600]: Invalid user sm0k3y from 83.222.230.90
Apr 21 08:09:01 [myhost] sshd[6600]: input_userauth_request: invalid user sm0k3y [preauth]
Apr 21 08:09:02 [myhost] sshd[6600]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]
Apr 21 08:09:03 [myhost] sshd[6604]: Invalid user cgi from 83.222.230.90
Apr 21 08:09:03 [myhost] sshd[6604]: input_userauth_request: invalid user cgi [preauth]
Apr 21 08:09:03 [myhost] sshd[6604]: Received disconnect from 83.222.230.90: 11: Bye Bye [preauth]

The screensharingd logs are as follows:

Apr 21 08:02:38 [myhost] screensharingd[5553]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 174.47.177.235 :: Type: VNC DES
Apr 21 08:02:57 --- last message repeated 7 times ---
Apr 21 08:28:42 [myhost] screensharingd[8520]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 208.71.217.153 :: Type: VNC DES
Apr 21 08:36:14 [myhost] screensharingd[9232]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 173.165.178.100 :: Type: VNC DES
Apr 21 08:43:34 [myhost] screensharingd[9928]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 5.135.101.206 :: Type: VNC DES
Apr 21 08:56:13 [myhost] screensharingd[11240]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 24.197.239.70 :: Type: VNC DES
Apr 21 08:56:34 [myhost] screensharingd[11273]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 24.197.239.70 :: Type: VNC DES
Apr 21 08:56:51 [myhost] screensharingd[11300]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 24.197.239.70 :: Type: VNC DES
Apr 21 08:56:58 --- last message repeated 1 time ---
Apr 21 09:29:15 [myhost] screensharingd[14752]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 75.150.95.108 :: Type: VNC DES
Apr 21 09:29:23 --- last message repeated 2 times ---
Apr 21 09:29:27 [myhost] screensharingd[14752]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 75.150.95.108 :: Type: VNC DES
Apr 21 09:29:33 --- last message repeated 1 time ---
Apr 21 09:29:59 [myhost] screensharingd[14819]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 75.150.95.108 :: Type: VNC DES
Apr 21 09:30:03 [myhost] screensharingd[14819]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 75.150.95.108 :: Type: VNC DES
Apr 21 09:30:13 --- last message repeated 2 times ---
Apr 21 09:30:14 [myhost] screensharingd[14819]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 75.150.95.108 :: Type: VNC DES
Apr 21 09:30:23 --- last message repeated 2 times ---
Apr 21 09:32:48 [myhost] screensharingd[15094]: Authentication: FAILED :: User Name: N/A :: Viewer Address: 61.160.201.25 :: Type: VNC DES

Obviously, I could manually add firewall rules using /Applications/Server.app/Contents/ServerRoot/usr/libexec/afctl -a [ip-address], but that is both time-consuming and pretty dumb. I've tried using some of the tools offered by my MacPorts tree, but they don't seem to work, and I'm concerned that anything I install might be conflicting with the built-in firewall.

Is there software for OS X that will automate firewall changes in response to repeated failed attempts or perhaps some other way to reduce the risk of brute force log in attempts succeeding?

Best Answer

If your server is on the public internet, it will get hundreds of automated log in attempts on whatever ports it listens. You will want to either set up an external firewall, use the existing ipfw/pfctl tools Apple ships or perhaps get a package like fail2ban which can be installed easily if you already have the homebrew tool.

You can test with ipfw and pfctl yourself and block a test IP from ssh and verify that there is no interference from Apple's firewall rules, but I've not experienced anyone that knows how to use the command line from breaking things if they have local access and know how to unconfigure a ruleset that has unintended consequences.

That would allow you to to have the firewall block repeated attempts after a threshold of failed attempts in a time range. It's not perfect, but can reduce the size of your log files and reduce the change someone will brute force an account or guess a common password.

This would be a good way to secure things if you can't use VPN or another firewall to reduce the number of listening ports your OS X server exposes to the internet in general.

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