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BZAR (Bro/Zeek ATT&CK-based Analytics and Reporting)

1. Introduction

The BZAR project uses the Bro/Zeek Network Security Monitor to detect ATT&CK-based adversarial activity.

MITRE ATT&CK is a publicly-available, curated knowledge base for cyber adversary behavior, reflecting the various phases of the adversary lifecycle and the platforms they are known to target. The ATT&CK model includes behaviors of numerous threats groups.

BZAR is a set of Bro/Zeek scripts utilizing the SMB and DCE-RPC protocol analyzers and the File Extraction Framework to detect ATT&CK-like activity, raise notices, and write to the Notice Log.

BZAR and CAR

BZAR is a component of the Cyber Analytics Repository. It was originally located within that library, but due to requirements for Zeek packages it was moved to its own repository. It's still managed as a component of CAR.

2. Tuning BZAR for Your Environment

BZAR must be tuned for your specific operational envrionment. For example, some of the ATT&CK-like activity that BZAR detects may be authorized and legitimate activity in your environment. Therefore, these detections would produce lots of unnecessary entries in the Notice Log. This can be tuned by the use of BZAR whitelists and by toggling on/off detection and/or reporting. See the CHANGES document for more information.

3. Complex Analytics for Detecting ATT&CK-like Activity

The BZAR analytics use the Bro/Zeek Summary Statistics (SumStats) Framework to combine two or more simple indicators in SMB and DCE-RPC traffic to detect ATT&CK-like activity with a greater degree of confidence. Three (3) BZAR analytics are described below.

3.1. SumStats Analytics for ATT&CK Lateral Movement and Execution

Use SumStats to raise a Bro/Zeek Notice event if an SMB Lateral Movement indicator (e.g., SMB File Write to a Windows Admin File Share: ADMIN$ or C$ only) is observed together with a DCE-RPC Execution indicator against the same (targeted) host, within a specified period of time.

Relevant ATT&CK Techniques

Relevant Indicators Detected by Bro/Zeek

NOTE: Preference would be to detect smb2_write_response event (instead of smb2_write_request), because it would confirm the file was actually written to the remote destination. Unfortunately, Bro/Zeek does not have an event for that SMB message-type yet.

3.2. SumStats Analytics for ATT&CK Lateral Movement (Multiple Attempts)

Use SumStats to raise a Bro/Zeek Notice event if multiple SMB Lateral Movement indicators (e.g., multiple attempts to connect to a Windows Admin File Share: ADMIN$ or C$ only) are observed originating from the same host, regardless of write-attempts and regardless of whether or not any connection is successful --just connection attempts-- within a specified period of time.

Relevant ATT&CK Techniques

Indicators detected by Bro/Zeek

3.3. SumStats Analytics for ATT&CK Discovery

Use SumStats to raise a Bro/Zeek Notice event if multiple instances of DCE-RPC Discovery indicators are observed originating from the same host, within a specified period of time.

Relevant ATT&CK Techniques

Relevant Indicator(s) Detected by Bro/Zeek

4. Simple Indicators for Detecting ATT&CK-like Activity

In addition to the analytics described above, BZAR uses simple indicators within SMB and DCE-RPC traffic to detect ATT&CK-like activity, although with a lesser degree of confidence than detection via the SumStats analytics. The BZAR indicators are grouped into six (6) categories, as described below.

4.1. Indicators for ATT&CK Lateral Movement

Raise a Bro/Zeek Notice event if a single instance of an SMB Lateral Movement indicator (e.g., SMB File Write to a Windows Admin File Share: ADMIN$ or C$ only) is observed, which indicates ATT&CK-like activity.

Relevant ATT&CK Techniques

Relevant Indicator(s) Detected by Bro/Zeek

NOTE: Preference would be to detect smb2_write_response event (instead of smb2_write_request), because it would confirm the file was actually written to the remote destination. Unfortunately, Bro/Zeek does not have an event for that SMB message-type yet.

4.2. Indicators for File Extraction Framework

Launch the Bro/Zeek File Extraction Framework to save a copy of the file associated with ATT&CK-like Lateral Movement onto a remote system. Raise a Bro Notice event for the Lateral Movement Extracted File.

Relevant ATT&CK Techniques

Relevant Indicator(s) Detected by Bro/Zeek

NOTE: Preference would be to detect smb2_write_response event (instead of smb2_write_request), because it would confirm the file was actually written to the remote destination. Unfortunately, Bro/Zeek does not have an event for that SMB message-type yet.

4.3. Indicators for ATT&CK Credential Access

Raise a Bro/Zeek Notice event if a single instance of any of the following Windows DCE-RPC functions (endpoint::operation) is observed, which indicates ATT&CK-like Credential Access techniques on the remote system.

Relevant ATT&CK Technique(s)

Relevant Indicator(s) Detected by Bro/Zeek

4.4. Indicators for ATT&CK Defense Evasion

Raise a Bro/Zeek Notice event if a single instance of any of the following
Windows DCE-RPC functions (endpoint::operation) is observed, which indicates ATT&CK-like Defense Evasion techniques on the remote system.

Relevant ATT&CK Techniques

Relevant Indicator(s) Detected by Bro/Zeek

4.5. Indicators for ATT&CK Execution

Raise a Bro/Zeek Notice event if a single instance of any of the following Windows DCE-RPC functions (endpoint::operation) is observed, which indicates ATT&CK-like Execution techniques on the remote system.

Relevant ATT&CK Technique(s)

Relevant Indicator(s) Detected by Bro/Zeek

4.6. Indicators for ATT&CK Persistence

Raise a Bro/Zeek Notice event if a single instance of any of the following Windows DCE-RPC functions (endpoint::operation) is observed, which indicates ATT&CK-like Persistence techniques on the remote system.

Relevant ATT&CK Technique(s):

Relevant Indicator(s) Detected by Bro/Zeek

4.7. Indicators for ATT&CK Impact

Raise a Bro/Zeek Notice event if a single instance of any of the following
Windows DCE-RPC functions (endpoint::operation) is observed, which indicates ATT&CK-like Impact techniques on the remote system.

Relevant ATT&CK Techniques

Relevant Indicator(s) Detected by Bro/Zeek

5. Additional DCE-RPC Interfaces and Methods

The BZAR project adds 144 more Microsoft DCE-RPC Interface UUIDs (a.k.a. "endpoints") to the Bro/Zeek DCE_RPC::uuid_endpoint_map.

The BZAR project also adds 1,145 Microsoft DCE-RPC Interface Methods (a.k.a. "operations") to the Bro/Zeek DCE_RPC::operations.

See the Bro/Zeek script 'bzar_dce-rpc_consts' for more information.

Most of the DCE-RPC endpoints and operations defined in 'bzar_dce-rpc_consts' were merged into Zeek's main product line, version 3.2.0-dev.565 | 2020-05-26 21:55:54 +0000. Ref: https://github.com/zeek/zeek/blob/master/scripts/base/protocols/dce-rpc/consts.zeek#L92

6. References

  1. Microsoft Developer Network (MSDN) Library. MSDN Library > Open Specifications > Protocols > Windows Protocols > Technical Documents. https://msdn.microsoft.com/en-us/library/jj712081.aspx
  2. Marchand, "Windows Network Services Internals". 2006. http://index-of.es/Windows/win_net_srv.pdf

7. Contributing

Contributions are welcome. This code is licensed under the same terms as the CAR repository. See the LICENSE file and the Developer Certificate of Origin certification in the CONTRIBUTING file in the root of the repository.

The information in this README file is current, as of 10/09/2020.

Copyright 2018 The MITRE Corporation. All Rights Reserved.
Approved for public release. Distribution unlimited. Case number 18-2489.