Cobalt Strike Potential Command and Control Traffic(18927)

[apackard]

Anyone seeing this new signature as FP prone?

[nigelswift]

We haven't seen any reported at this point.

[mivaldi]

The signature is meant to detect an empty space in "HTTP/1.1 200 OK " (right after the OK) in HTTP responses, which may indicate a connection with a NanoHTTPD server, which is 'typically' used in Cobalt Strike's team server.

If you see other HTTPD implementations inserting the "extraneous space", do let us know.

More information available at:

https://blog.fox-it.com/2019/02/26/identifying-cobalt-strike-team-servers-in-the-wild/

[apackard]

Hi, yes, I guessed that might be what you defined the signature for.

We are seeing hits on this, obviously hoping that it’s a false positive.....

It seems to be triggering on valid websites as far as we can tell, and it’s not just one, so either there are a lot of compromised commercial websites or it’s too sensitive.  I can provide the packet captures as necessary.

[apackard]

As a FYI here are three domains we're seeing hits on:-

www.merrell.com

www.belk.com

www.hotelchocolat.com

Rgds

[PaulT]

We are seeing what we think are false postives with this signature.  We see lots of OCSP traffic from Amazon and others that has space after the 200 OK.

POST / HTTP/1.0

Connection: Keep-Alive

Content-Type: application/ocsp-request

Accept: */*

User-Agent: Entrust Entelligence Security Provider

Content-Length: 121

Host: ocsp.rootg2.amazontrust.com

0w0u.....0N0L0J0...+.......}.D^g.|.wNC..>...s...._.....0+8...mJ..........J*'.....+.........0.0.. +.....0...

0.. +.....0..HTTP/1.1 200 OK

Content-Type: application/ocsp-response

Content-Length: 1546

Connection: keep-alive

Date: Fri, 29 Mar 2019 09:56:06 GMT

Server: WEBrick/1.3.1 (Ruby/2.3.8/2018-10-18)

X-Cache: Miss from cloudfront

Via: 1.1 048de604b26de968a1aa2fe5dd1a0085.cloudfront.net (CloudFront)

X-Amz-Cf-Id: xuBEvyqfYSM9Hr0TcWIUJ-CL-n_a8enx3EmVPtId3MItOJgncm_6ew==

[ChrisThuys]

We are also see ing lots of hits for  this signature on ocsp.rootca1.amazontrust.com

[GuillaumeD]

Hello community,

We have also the same threats traffic detected on our Palo devices and watching to the traffic itself it seems to be ocsp traffic on serveral legitimate servers around amazon, cloudfront...

Can we safely consider this traffic as false positive detection?

Thank you in advance,

Guillaume

[mivaldi]

I believe that's the reason why this was named "Potential" with "informational" severity. Its definition hints you that the signature is lose enough to be FP prone.

[stevenkadish]

Here's a few domains that have been triggering the FP for us:

store.moma.org
www.saucony.com
www.bcbg.com

The common denominator seems to be shopping (apparently all our users do) and that all the IPs are hosted on Cloudflare.

Thanks,

- Steve