If you run a web server and you take a look at the logs, you will likely have seen something like this appearing:

xxx.xxx.xxx.xxx - - [01/May/2013:18:32:36 +0100] "GET /w00tw00t.at.ISC.SANS.DFind:)
HTTP/1.1" 400 320 "-" "-"

This is the product of a tool called w00tw00t, which is used by nefarious script kiddies to probe and attempt to compromise your server. If your server is up-to-date, there is probably not too much to worry about (without wanting to jinx it), however since a strength in depth approach is always the best plan when it comes to security, it is probably a good idea if we could deploy some additional countermeasures.

A common tactic is to use a tool like fail2ban to monitor your logs and then firewall off the offenders IP address, and there are filters out there to do this.

However, like a lot of people, I use the caching proxy Squid, in reverse proxy mode, to help handle high load on a web server. Since, in this configuration, Apache (and therefore fail2ban’s standard w00tw00t rules) will see these requests as coming from the cache machine, we need to take another approach.

One option is to modify the Apache log format to use the X-Forwarded-For variable instead (details of how can be found here), and thus preserving the original IP address in the logs. However, this would require me to modify a number of vhosts, and it seemed simpler to monitor the one squid access log.

So, I wrote a quick fail2ban filter to catch w00tw00t scans and block the offending IP address.

In jail.local

enabled = true
filter = squid-w00tw00t
port = all
logpath = /var/log/squid/access.log
maxretry = 1

In filter.d/squid-w00tw00t.conf

# Fail2Ban configuration file to catch w00tw00t scans on squid reverse proxy settings
# Author: Marcus Povey


# Read common prefixes. If any customizations available -- read them from
# common.local
before = common.conf


_daemon = squid

# Option: failregex
# Notes.: regex to match the password failures messages in the logfile. The
# host must be matched by a group named "host". The tag "" can
# be used for standard IP/hostname matching and is only an alias for
# (?:::f{4,6}:)?(?P<host>[\w\-.^_]+)
# Values: TEXT
failregex = <HOST> TCP_.*http.*/(w00tw00t|wootwoot|WootWoot|WooTWooT).*$

# Option: ignoreregex
# Notes.: regex to ignore. If this regex matches, the line is ignored.
# Values: TEXT
ignoreregex =

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