Detecting and blocking Phishing with Snort and ClamAV

ClamAV is a great Open Source virusscanner that can be used for detecting virusses from Snort or Snort_inline using the ClamAV preprocessor. However, by using the anti-phishing and anti-scam signatures by SaneSecurity, this combination can also be used to detect and block phishing and scam attempts. Here is how to set it up.

I’ve decided to run this on my gateway, which is a slow machine. Because I don’t want all my traffic to slow down to much, I’m not going to run the ClamAV defs, only the anti-phishing ones. The default location of the defs on my Debian Sarge system is /var/lib/clamav, so I’ve created a new directory called ‘/var/lib/clamav-phish’. Next I’ve downloaded the defs from SaneSecurity. After unzipping them and the defs were ready.

Next was setting up the clamav preprocessor. For this I used the config line in my snort config:

preprocessor clamav: ports 80, dbreload-time 3600, dbdir /var/lib/clamav-phish, action-drop, toclientonly

This line says that spp_clamav should look for traffic on port 80 that flows to the client. It should use the signatures in /var/lib/clamav-phish/ and it should drop the traffic if a phishing attempt is detected. It also checks once an hour to see if the defs in the directory have been updated, and reloads them if so.

William Metcalf pointed me to a site where you can test this setup. It’s called MillerSmiles.co.uk and it’s an anti-phishing site, with many examples on their site. Opening an example shows this in my snort_inline log:

11/12-18:44:29.581771 [**] [129:1:1] (spp_clamav) Virus Found: Html.Phishing.Bank.Gen636.Sanesecurity.06051701 [**] {TCP} 209.85.50.12:80 -> 192.168.1.2:34915

The site failed to open, so it works just fine!

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