Temporary "solution" to MyDoom worm

[Fabio Bastiglia Oliva <fboliva () safenetworks com>]

Hi guys,


hehe...  After  all  this years posting to some lists, also talking to
foreign  friends,  I  could not make my english better... so... before
anything else, sorry about my bad english. :)

I've  mada  a  piggy  solution to make MyDoom worm (Novarg.A, Shimg.A,
Mimail.R)  stop  hitting  mail  servers. It's not the best solution, I
know,  but  these rules can help if you have some kind of mail scanner
to  your mail server, this rules will make the mail server's cpu usage
decrease.

I'm using the MyDoom possible Subjects to detect it... Of course, it's
not 100% accurate, but it's helping a lot my mail servers.

It's necessary to use Flexible Response to make it work.

Below is the FlexResp config I'm using to this rule.
var RESP_TCP_URG resp:rst_all

These  are  the  rules:

alert tcp any any -> any 25 (msg:"Possible MyDoom Worm Incoming"; flow:to_server,established; content:"Subject\: 
Error"; nocase; classtype:misc-activity; rev:1;$RESP_TCP_URG;)
alert tcp any any -> any 25 (msg:"Possible MyDoom Worm Incoming"; flow:to_server,established; content:"Subject\: 
Status"; nocase; classtype:misc-activity; rev:1;$RESP_TCP_URG;)
alert tcp any any -> any 25 (msg:"Possible MyDoom Worm Incoming"; flow:to_server,established; content:"Subject\: Server 
Report"; nocase; classtype:misc-activity; rev:1;$RESP_TCP_URG;)
alert tcp any any -> any 25 (msg:"Possible MyDoom Worm Incoming"; flow:to_server,established; content:"Subject\: Mail 
Transaction Failed"; nocase; classtype:misc-activity; rev:1;$RESP_TCP_URG;)
alert tcp any any -> any 25 (msg:"Possible MyDoom Worm Incoming"; flow:to_server,established; content:"Subject\: Mail 
Delivery System"; nocase; classtype:misc-activity; rev:1;$RESP_TCP_URG;)
alert tcp any any -> any 25 (msg:"Possible MyDoom Worm Incoming"; flow:to_server,established; content:"Subject\: 
Hello"; nocase; classtype:misc-activity; rev:1;$RESP_TCP_URG;)
alert tcp any any -> any 25 (msg:"Possible MyDoom Worm Incoming"; flow:to_server,established; content:"Subject\: Hi"; 
nocase; classtype:misc-activity; rev:1;$RESP_TCP_URG;)
alert tcp any any -> any 25 (msg:"Possible MyDoom Worm Incoming"; flow:to_server,established; content:"Subject\: Test"; 
nocase; classtype:misc-activity; rev:1;$RESP_TCP_URG;)

Best Regards
________________________
Fabio Bastiglia Oliva
fboliva () safenetworks com



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