name: Detect Regasm with Network Connection
id: 07921114-6db4-4e2e-ae58-3ea8a52ae93f
version: 1
date: '2021-02-16'
author: Michael Haag, Splunk
type: batch
datamodel: []
description: The following analytic identifies regasm.exe with a network connection
  to a public IP address, exluding private IP space. This particular technique has
  been used in the wild to bypass application control products. Regasm.exe and Regsvcs.exe
  are signed by Microsoft. By contacting a remote command and control server, the
  adversary will have the ability to escalate privileges and complete the objectives.
  During investigation, identify and retrieve the content being loaded. Review parallel
  processes for additional suspicious behavior. Gather any other file modifications
  and review accordingly. Review the reputation of the remote IP or domain and block
  as needed. regsvcs.exe and regasm.exe are natively found in C:\Windows\Microsoft.NET\Framework\v*\regasm|regsvcs.exe
  and C:\Windows\Microsoft.NET\Framework64\v*\regasm|regsvcs.exe.
search: '`sysmon` EventID=3 dest_ip!=10.0.0.0/12 dest_ip!=172.16.0.0/12 dest_ip!=192.168.0.0/16
  process_name=regasm.exe | rename Computer as dest | stats count min(_time) as firstTime
  max(_time) as lastTime by dest, User, process_name, src_ip, dest_host, dest_ip |
  `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `detect_regasm_with_network_connection_filter`'
how_to_implement: To successfully implement this search, you need to be ingesting
  logs with the process name, parent process, and command-line executions from your
  endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the
  Sysmon TA.
known_false_positives: Although unlikely, limited instances of regasm.exe with a network
  connection may cause a false positive. Filter based endpoint usage, command line
  arguments, or process lineage.
references:
- https://attack.mitre.org/techniques/T1218/009/
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1218.009/T1218.009.md
- https://lolbas-project.github.io/lolbas/Binaries/Regasm/
tags:
  analytic_story:
  - Suspicious Regsvcs Regasm Activity
  asset_type: Endpoint
  automated_detection_testing: passed
  cis20:
  - CIS 8
  dataset:
  - https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1218.009/atomic_red_team/windows-sysmon.log
  kill_chain_phases:
  - Actions on Objectives
  mitre_attack_id:
  - T1218.009
  nist:
  - PR.PT
  - DE.CM
  product:
  - Splunk Enterprise
  - Splunk Enterprise Security
  - Splunk Cloud
  required_fields:
  - _time
  - EventID
  - dest_ip
  - process_name
  - Computer
  - User
  - src_ip
  - dest_host
  - dest_ip
  security_domain: endpoint
