Carbon Black User Added Outside Org

AnalysisType: rule
RuleID: "CarbonBlack.Audit.User.Added.Outside.Org"
LogTypes:
  - CarbonBlack.Audit
Description: "Detects when a user from a different organization is added to Carbon Black."
DisplayName: "Carbon Black User Added Outside Org"
Enabled: true
Filename: cb_audit_user_added_outside_org.py
Severity: High
Tags:
  - Persistence
  - Create Account
Reports:
  MITRE ATT&CK:
    - TA0003:T1136
Reference: https://docs.vmware.com/en/VMware-Carbon-Black-Cloud/services/carbon-black-cloud-user-guide/GUID-516BAF8C-A13D-4FC7-AA92-923159C13083.html
Threshold: 1
DedupPeriodMinutes: 60
Tests:
  - Name: Outside org
    ExpectedResult: true
    Log:
      {
        "clientIp": "12.34.56.78",
        "description": "Added user badguy@acme.io to org 12345 (Email Invitation)",
        "eventId": "d109e568832111ee8ab2057b240e65f8",
        "eventTime": "2023-11-14 19:12:55.917000000",
        "flagged": false,
        "loginName": "bob.ross@acme.com",
        "orgName": "acme.com",
        "verbose": false,
      }
  - Name: Inside org
    ExpectedResult: false
    Log:
      {
        "clientIp": "12.34.56.78",
        "description": "Added user goodguy@acme.com to org 12345 (Email Invitation)",
        "eventId": "d109e568832111ee8ab2057b240e65f8",
        "eventTime": "2023-11-14 19:12:55.917000000",
        "flagged": false,
        "loginName": "bob.ross@acme.com",
        "orgName": "acme.com",
        "verbose": false,
      }


# ------ paired body: cb_audit_user_added_outside_org.py ------

PATTERNS = ("Added user ",)


def rule(event):
    desc = event.get("description", "")
    if not any(desc.startswith(pattern) for pattern in PATTERNS):
        return False
    src_user = event.get("loginName", "")
    src_domain = src_user.split("@")[1]
    dst_user = desc.split(" ")[2]
    dst_domain = dst_user.split("@")[1]
    if src_domain != dst_domain:
        return True
    return False


def title(event):
    user = event.get("loginName", "<NO_USERNAME_FOUND>")
    ip_addr = event.get("clientIp", "<NO_IP_FOUND>")
    desc = event.get("description", "<NO_DESCRIPTION_FOUND>")
    return f"{user} [{ip_addr}] {desc}"