[Snort-sigs] Telnet rule doesn't work

Paul Li paul at scybersecurity.com
Sat Jun 24 06:53:00 EDT 2017

I'm using Snort 2.9.9 on Ubuntu 16.04. Trying to build a telnet login
detection rule as the following:

alert tcp $TELNET_SERVERS 23 -> $EXTERNAL_NET any (msg:"TELNET login
incorrect"; content:"Login incorrect"; nocase;classtype:bad-unknown;
sid:429; rev:2; priority:1;)

This rule looks good to me but it doesn't fire when failed TELNET occurs.
Any thing missing in this rule?

NOTE: At the same time, I created a SSH rule as the following that works

alert tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"SSH login attempt";
flow:to_server,established; content:"SSH-"; sid:10000002; rev:3;

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