[Snort-sigs] Content-Type: application/x-www-form-urlencoded allows bypass of my snort rule

Y M snort at ...3751...
Sat Jan 28 09:42:32 EST 2017


You are using the file_data buffer, which as far as I know is used with responses, however, your rule is attempting to trigger on requests through the rule direction and the flow configuration, or at least that's what I am seeing. Please correct me if I misunderstood your question.

If you remove the file_data from the rule, what happens?

Also if you want to be more specific in your rule, you can add a content detection to detect the content-type header.

YM

_____________________________
From: Avery Rozar <avery.rozar at ...4102...<mailto:avery.rozar at ...4102...>>
Sent: Saturday, January 28, 2017 5:34 PM
Subject: [Snort-sigs] Content-Type: application/x-www-form-urlencoded allows bypass of my snort rule
To: <snort-sigs at lists.sourceforge.net<mailto:snort-sigs at ...1306...et>>


I'm trying to setup a rule to deny anyone that is not coming from $VPN_NET from attempting to log into word press.

# in snort.conf
ip var VPN_NET [cidr,cidr]

# in local.rules
drop tcp !$VPN_NET any -> $HOME_NET any (msg:"WordPress Login attempt"; flow:to_server,established; file_data; content:"wp-login"; nocase; content: "POST"; nocase; http_method; classtype:misc-activity; sid:500001; rev:1; metadata:policy balanced-ips drop, policy security-ips drop, service http;)


This rule seems to stop anything unless the POST is using 'Content-Type: application/x-www-form-urlencoded'. What is the best way to allow snort to deal with urlencoded POSTs, or is my rule just jacked up?


Thanks,
Avery


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