[Snort-sigs] BOTNET-CNC Possible host infection - excessive DNS queries for .eu

Martin Holste mcholste at ...2420...
Mon Mar 12 11:14:35 EDT 2012


The sig, as written, will false like crazy on any medium or large
sized network because it does not take into account DNS servers or
SMTP servers (or spam gateways) which do a lot of DNS lookups.

On Mon, Mar 12, 2012 at 9:41 AM, Alex Kirk <akirk at ...435...> wrote:
> First, you need the ".eu" bit because you need to have a content match in
> the rule, else performance will suffer massively. Second, and more
> important, the behavior we've seen centers around this particular TLD (and a
> couple of others for which we have rules); we're targeting there to keep
> false positives down.
>
> As far as this picking up other malware - chances are high it will. The rule
> of thumb is to take a look at the domain names in the alerts, and determine
> whether they're legitimate or not (which is usually obvious because
> malicious ones are randomized), and then track back to the boxes generating
> the queries for a thorough scan/investigation.
>
> On Sun, Mar 11, 2012 at 8:00 AM, Yew Chuan Ong <yewchuan88 at ...2420...> wrote:
>>
>> Hi,
>>
>> alert udp $HOME_NET any -> $EXTERNAL_NET 53 (msg:"BOTNET-CNC Possible host
>> infection - excessive DNS queries for .eu"; flow:to_server;
>> byte_test:1,!&,0xF8,2; content:"|02|eu|00|"; fast_pattern:only;
>> detection_filter:track by_src, count 100, seconds 10;
>> classtype:trojan-activity; sid:21544; rev:1;)
>>
>> This is the new sig posted on VRT blog recently which aimed to find out
>> malware within the network. I am wondering why we need to specific on the
>> keyword ".eu". Can we tracked the related traffic by using only the
>> threshold?
>>
>> Also, are we aiming on any specific malware besides Murofet and Kazy? I
>> try to google around but can't really get it. Thanks!
>>
>>
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>
>
>
>
> --
> Alex Kirk
> AEGIS Program Lead
> Sourcefire Vulnerability Research Team
> +1-410-423-1937
> alex.kirk at ...435...
>
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