HOWTO Setup Deny Hosts

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Purpose

Fail2ban, working in combination with iptables, is our favoured method of controlling crack-attempts. Fail2ban is reactionary though (responding as/after attacks occur), and is best-used only on a real server. Denyhosts makes use of a collaborative, on-line list of attackers, and can therefore be very pro-active in blocking crack-attempts. So, we're testing defence-in-depth by applying both fail2ban and denyhosts on some machines. In addition, our virtual servers (Gentoo Linux Vserver guests) cannot directly address hardware, do not run iptables, and cannot use fail2ban - Denyhosts is a great security addition to a Vserver-guest.

Setup

  • If ssh is not compiled tcpd you will need to edit make.conf and recompile.
hostname ~ # emerge -pv net-misc/openssh
[ebuild   R ] net-misc/openssh-x.x  USE="tcpd"
  • There will be more USE flags listed in addition to tcpd but it is the only necessary flag for this setup.
hostname ~ # emerge -v denyhosts
[ebuild   N ] app-admin/denyhosts-x.x

Manually create a missing file: 

hostname ~ # touch /var/lib/denyhosts/sync-timestamp
  • Denyhosts can be run as a cron job, but we run it as as service:
hostname ~ # rc-update add denyhosts default

Configure

  • There are several values to change in denyhosts.conf. Refer to the comments in this file for more information.
hostname ~ # emacs -nw /etc/denyhosts.conf

PURGE_DENY =2h

PURGE_THRESHOLD = 3

BLOCK_SERVICE  = ALL

REM out BLOCK_SERVICE  = sshd

DENY_THRESHOLD_ROOT = 4

SYSLOG_REPORT=YES

SYNC_SERVER = http://xmlrpc.denyhosts.net:9911

SYNC_INTERVAL = 1h

SYNC_UPLOAD = yes

SYNC_DOWNLOAD = yes

SYNC_DOWNLOAD_THRESHOLD = 3


Problems arise when friendly folks attempt to access services and fail. This is especially harsh when an automated tool attempts to re-access a service repeatedly with the failing credentials, and before the user can even react, they are blocked :-( We add entries to /etc/hosts.allow to try to prevent this: 

hostname ~ # emacs -nw /etc/hosts.allow

# SFU IP ADDRESSES.  Taken from http://whois.arin.net/rest/org/SFU-1/nets on March 6, 2012. GRP.
#192.75.241.0/11 142.58.0.0/16  209.87.56.0/24 206.12.128.0/8 206.12.30.0/8 207.23.85.0/8 204.244.192.168/3 199.60.0.0/12                                               

# SHAW IP ADDRESSES.  Taken from http://whois.arin.net/rest/org/SHAWC/nets on March 6, 2012. GRP.
#174.0.0.0/13 184.64.0.0/13 204.209.208.0/21 204.244.240.0/9 24.108.0.0/15 24.64.0.0/13 24.70.0.0/15 24.71.223.0/24 24.76.0.0/15 24.80.0.0/13 24.244.0.0/18 50.64.0.0/13 68.144.0.0/11 70.64.0.0/12 96.48.0.0/13 64.59.128.0/18 66.163.64.0/20                                                                                                            

# TELUS IP ADDRESSES.  Taken from http://whois.arin.net/rest/org/TACE/nets on March 6, 2012. GRP.
#204.209.208.0/11 24.108.0.0/15 64.59.128.0/18 142.60.0.0/16 137.186.0.0/16 206.75.0.0/16 207.81.0.0/16 207.134.0.0/16 154.5.0.0/16 204.174.120.0/15 209.115.222.0/8 204.174.64.0/11 142.169.0.0/16 142.168.0.0/16 199.84.240.0/10 64.180.0.0/16 50.92.0.0/15 216.226.32.0/13 206.162.128.0/14 66.110.128.0/14 207.102.0.0/16 206.108.16.0/12 207.34.128.0/14 207.194.0.0/16 208.181.0.0/16 209.52.0.0/16 204.174.211.0/11 206.108.192.0/13 64.114.0.0/16 209.115.128.0/15 161.184.64.0/11 209.107.96.0/13 154.5.0.0/16 207.228.64.0/14 207.148.128.0/14 209.91.64.0/14 205.236.24.0/8 205.236.48.0/8 209.104.64.0/14 207.167.192.0/14 154.11.0.0/16 216.123.192.0/14 207.229.0.0/14 208.38.0.0/14 199.212.152.0/11 204.225.240.0/11 207.34.192.0/14 209.20.0.0/14 209.121.0.0/16 206.108.64.0/13 209.89.0.0/16 205.206.0.0/16 209.162.160.0/12 204.191.0.0/16 205.250.0.0/16 207.81.0.0/16 209.171.0.0/16 209.29.0.0/16 198.53.0.0/16 206.116.0.0/16 198.166.0.0/16 206.75.0.0/16 207.216.0.0/16 207.6.0.0/16 66.222.128.0/15 207.134.0.0/16 216.218.0.0/14 137.186.0.0/16 199.126.0.0/16 209.202.64.0/14 66.203.192.0/13 207.219.0.0/16 216.232.0.0/16 209.53.0.0/16 66.183.0.0/16 207.34.64.0/14 206.26.204.192/14 205.138.102.0/8 207.6.32.0/13 206.116.224.0/11 173.180.0.0/16 205.138.98.0/8 108.172.0.0/16 75.152.0.0/16 154.20.0.0/16 99.199.0.0/16 50.98.0.0/16 23.16.0.0/16                                                                                 

# DELTA CABLE IP ADDRESSES.  Taken from http://whois.arin.net/rest/org/DLTA/nets on March 6, 2012. GRP.
#24.207.0.0/15

SSHD: 127.0.0.1/8 192.75.241.0/11 142.58.0.0/16  209.87.56.0/24 206.12.128.0/8 206.12.30.0/8 207.23.85.0/8 204.244.192.168/3 199.60.0.0/12 174.0.0.0/13 184.64.0.0/13 204.209.208.0/21 204.244.240.0/9 24.108.0.0/15 24.64.0.0/13 24.70.0.0/15 24.71.223.0/24 24.76.0.0/15 24.80.0.0/13 24.244.0.0/18 50.64.0.0/13 68.144.0.0/11 70.64.0.0/12 96.48.0.0/13 64.59.128.0/18 66.163.64.0/20 204.209.208.0/11 24.108.0.0/15 64.59.128.0/18 142.60.0.0/16 137.186.0.0/16 206.75.0.0/16 207.81.0.0/16 207.134.0.0/16 154.5.0.0/16 204.174.120.0/15 209.115.222.0/8 204.174.64.0/11 142.169.0.0/16 142.168.0.0/16 199.84.240.0/10 64.180.0.0/16 50.92.0.0/15 216.226.32.0/13 206.162.128.0/14 66.110.128.0/14 207.102.0.0/16 206.108.16.0/12 207.34.128.0/14 207.194.0.0/16 208.181.0.0/16 209.52.0.0/16 204.174.211.0/11 206.108.192.0/13 64.114.0.0/16 209.115.128.0/15 161.184.64.0/11 209.107.96.0/13 154.5.0.0/16 207.228.64.0/14 207.148.128.0/14 209.91.64.0/14 205.236.24.0/8 205.236.48.0/8 209.104.64.0/14 207.167.192.0/14 154.11.0.0/16 216.123.192.0/14 207.229.0.0/14 208.38.0.0/14 199.212.152.0/11 204.225.240.0/11 207.34.192.0/14 209.20.0.0/14 209.121.0.0/16 206.108.64.0/13 209.89.0.0/16 205.206.0.0/16 209.162.160.0/12 204.191.0.0/16 205.250.0.0/16 207.81.0.0/16 209.171.0.0/16 209.29.0.0/16 198.53.0.0/16 206.116.0.0/16 198.166.0.0/16 206.75.0.0/16 207.216.0.0/16 207.6.0.0/16 66.222.128.0/15 207.134.0.0/16 216.218.0.0/14 137.186.0.0/16 199.126.0.0/ 16 209.202.64.0/14 66.203.192.0/13 207.219.0.0/16 216.232.0.0/16 209.53.0.0/16 66.183.0.0/16 207.34.64.0/14 206.26.204.192/14 205.138.102.0/8 207.6.32.0/13 206.116.224.0/11 173.180.0.0/16 205.138.98.0/8 108.172.0.0/16 75.152.0.0/16 154.20.0.0/16 99.199.0.0/16 50.98.0.0/16 23.16.0.0/16 24.207.0.0/15

ALL:  192.75.241.0/11 142.58.0.0/16  209.87.56.0/24 206.12.128.0/8 206.12.30.0/8 207.23.85.0/8 204.244.192.168/3 199.60.0.0/12

Turn It On

hostname ~ # /etc/init.d/denyhosts start

Problems?

Try: 

 hostname ~ # tail -f  /var/log/denyhosts

Also - given the above settings, it takes one hour (1h) after starting the denyhost daemon before a sync to the denyhost-server is attempted.

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