WEB-CLIENT Excel malformed FBI record - False positive?

[Jesper Skou Jensen <jesper.skou.jensen () uni-c dk>]

Hi there,

I've recently deployed a passive Snort sniffer next a bunch of 
webservers, and I'm getting quite a lot of "WEB-CLIENT Excel malformed 
FBI record" reports. I can't quite figure out if it's false positives or 
not.

I've configured the IP's of the webservers as $HOME_NET, but when I look in
"rules/web-client.rules"

it states
"alert tcp $EXTERNAL_NET $HTTP_PORTS -> $HOME_NET any"

which I read as the $HOME_NET is the destination, BUT when I read the 
Snort syslog message below, it looks like the "attack" originates from 
my webserver. Is that a correct assumption?

(Timestamp and IPs have been changed to protect the innocent! :-)
Jul  7 13:37:00 sysloghost snort: [1:12256:1] WEB-CLIENT Excel malformed 
FBI record [Classification: Attempted User Privilege Gain] [Priority: 
1]: {TCP} 10.1.1.1:80 -> 10.2.2.2:1229

10.1.1.1 is the webserver
10.2.2.2 is some client


Can any of you guys enlighten me?


-- 

   Jesper S. Jensen
Basisnet og Sikkerhed
Uni-C - Århus, Danmark

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