[Snort-sigs] Proposed Sirefef (was Re: Late in the day...bet this could be sig'd)

waldo kitty wkitty42 at ...3507...
Mon May 6 17:04:52 EDT 2013


On 5/6/2013 13:37, Joel Esler wrote:
> On May 3, 2013, at 8:54 PM, lists at ...3397... <mailto:lists at ...3397...>
> wrote:
>> alert tcp $EXTERNAL_NET $HTTP_PORTS -> $HOME_NET any (msg:"ET
>> CURRENT_EVENTS/VRT_COMMUNITY Potential Sirefef hostile executable served from
>> compromised or malicious WordPress site"; flow:established,from_server;
>> content:"/wp-content/"; http_uri; content:".exe|20|HTTP/1."; fast_pattern:only;
>> pcre:"/\/\d+\.exe$/U"; classtype:trojan-activity;
>> reference:url,blog.avast.com/2013/05/03/regents-of-louisiana-spreading-sirefef-malware
>> <http://blog.avast.com/2013/05/03/regents-of-louisiana-spreading-sirefef-malware>;
>> sid:x; rev:1;)
>
> Nathan,
>
> Looking at what you are intending here, I think you mean it the other way
> (HOME_NET -> $EXTERNAL_NET)

ok... now i'm officially confused... the flow in the rule is "from_server"... 
with that specified, does it really matter if HOME_NET or EXTERNAL_NET come first?

then there's the situation of not only detecting this coming into a network from 
an external server, but also of detecting this going out of a network that runs 
servers feeding the public on the outside...

does the '->' really make any difference?

should it instead have been '<-' if the rule writer really wanted HOME_NET to be 
first?

would using '<->' or '<>' (if either is allowed) detect the traffic no matter 
which way the traffic was going (internal server to external client or external 
server to internal client) no matter where the server is located??

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