[Zeek-Dev] [EXT] Zeek DCE-RPC Analyzer Update

Mon Sep 23 06:35:37 PDT 2019

Hi Gabriele,

Thank you for the compliment on BZAR.  I think it would be great if you were to create a parser for those data stubs.  That would add a lot of value.

>> ...nor for the classic code execution dcerpc traffic passed through

>> named pipes (atsvc, svcctl, winreg , [...]) (authlevel connect), which

>> are the easiest techniques to exploit with basic AD configuration.

I am surprised those RPC interfaces are not encrypted.  For example, the current MSDN documentation states the RPC authentication should be Level 6 (authlevel packet privacy) for atsvc, svcctl, and winreg, which would mean the data stubs would be encrypted.  I didn’t investigate further to verify if that is true or not, or to find cases when it is not encrypted.

Thanks,

Mark

From: Gabriele Pippi <g.pippi at certego.net> 
Sent: Monday, September 23, 2019 6:19 AM
To: Fernandez, Mark I <mfernandez at mitre.org>
Cc: zeek-dev at zeek.org
Subject: Re: [EXT] [Zeek-Dev] Zeek DCE-RPC Analyzer Update

Hi Mark,

I have already analyzed your project and I thank you for the excellent work.

The reasons why we are looking for something more are these:

1. Currently analyzing the new techniques with DCOM we have noticed that neither the endpoints nor the operations have been included in the project.
2. We have also noticed in the observed cases that the data stub is encrypted using ntlmssp authlevel packet privacy, this happened in the cases where dcerpc passed over pure  through a specific rule on the local windows firewall. However this does not happen neither for the observed cases of DCOM (authlevel packet integrity), nor for the classic code execution dcerpc traffic passed through named pipes (atsvc, svcctl, winreg , [...]) (authlevel connect), which are the easiest techniques to exploit with basic AD configuration. This type of traffic is legitimate and widely used in our networks, the content of the stub data in cleartext would help us both to filter the normal uses from the malicious ones and to greatly increase the quality of our analyzes.

Thanks,

Gabriele.

Il giorno ven 20 set 2019 alle ore 13:19 Fernandez, Mark I <mfernandez at mitre.org <mailto:mfernandez at mitre.org> > ha scritto:

Hi Gabriele,

Last year I did a deep-dive into the Zeek DCE-RPC protocol analyzer.  I found the same un-used binpac file endpoint-atsvc.pac, and I had similar thoughts about developing analyzers for specific RPC data stubs.  Unfortunately, so many RPC data stubs are encrypted by default now.  Also, I realized I was able to make useful decisions from just knowing the RPC interface and method and then mapping that function to a threat model.  Please see the github repository at the URL below.  Also, I am giving a talk on it at ZeekWeek next month.

https://github.com/mitre-attack/bzar

Thanks,

Mark

From: zeek-dev-bounces at zeek.org <zeek-dev-bounces at zeek.org <mailto:zeek-dev-bounces at zeek.org> > On Behalf Of Gabriele Pippi
Sent: Thursday, September 19, 2019 12:10 PM
To: zeek-dev at zeek.org <mailto:zeek-dev at zeek.org> 
Subject: [EXT] [Zeek-Dev] Zeek DCE-RPC Analyzer Update

Zeek-Dev Group,

hi i'm Gabriele from purple team of Certego. We are trying to rely on zeek to increase the detection of our platform in the moving through the internal network scenario ( credential access, discovery and specially lateral movement ATT&CK Matrix phases).

In the case of dcerpc for the moment we are correlating the information generated by bro_dce_rpc parser with data coming from endpoint agents.

In order to reduce the number of false positives and to gather more detailed information for a possible analysis, we thought it would be really interesting "to get extensive parsing in place for DCE-RPC messages by parsing the IDL files [...]" or to implement a "byte string containing the stub data itself" in case it is not encrypted. In our case we would like to give priority to all those operations that allow to directly carry out an entire attack or a code execution, restricting the scope to those with stub data in cleartext (for example in the case of dcerpc over smb named_pipe or in the case of dcom, at least for the operations observed until now ). I found the following BINPAC zeek/src/analyzer/protocol/dce-rpc/endpoint-atsvc.pac, and I ended up to this discussion https://bro-dev.bro-ids.narkive.com/jq0Ofe6L/bro-dce-rpc-analyzer-questions . 

Have there been any updates regarding this topic? Do you have any advice on how to proceed?

Once we have assessed the feasibility, we could be willing to contribute to achieve this goal. In this work we would also like to insert a series of endpoints and operations that currently are not mapped by zeek, among those observed for example there are several in DCOM. Once the tests are completed, if you are interested, we could also provide you with an exhaustive list or integrate it directly with a possible merge.

At the moment we do not know of the existence of technologies that allow to do alerting on some types of Windows APIs, we therefore believe that being able to do it at the network level through DCERPC is an important added value to zeek.

Thanks,

Gabriele.

-- 

 <http://www.certego.net/> 

Gabriele Pippi

Incident Response Team, Certego

 <tel:+39-059-7353333> 

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