Atomic Red Team Testing

Atomic Red Team Testing Skill

Configuration

Required environment variables:

Target placeholders used in this guide:

• <TARGET_IP> — IP address of the test endpoint
• <TARGET_NAME> — Hostname of the test endpoint (e.g., ar-win-1)

Pragmatic Testing Philosophy

Detection engineering is iterative. The goal is NOT to run every atomic against every target — it is to generate the specific telemetry your detection needs and confirm the detection fires.

Core principles:

1. Test what you're detecting. Pick atomics that produce the exact event your SPL/Sigma/KQL query looks for.
2. One technique at a time. Isolate variables. Run one atomic, check for logs, validate the detection, then move on.
3. Fast feedback loops. Deploy → Execute → Wait → Validate. If something breaks, fix it and re-run — don't over-plan.
4. Custom atomics fill gaps. When no standard atomic covers your detection scenario, write a T9999.XXX custom atomic instead of forcing a bad fit.
5. Validate telemetry first, detection second. If the right events aren't reaching your SIEM, the detection can't fire. Always confirm log ingestion before blaming the query.

Running Standard Atomics

Via Invoke-AtomicRedTeam (PowerShell on target)

# List available tests for a technique
Invoke-AtomicTest T1059.001 -ShowDetailsBrief

# Run a specific test number
Invoke-AtomicTest T1059.001 -TestNumbers 1

# Run with prerequisite check and install
Invoke-AtomicTest T1059.001 -TestNumbers 1 -GetPrereqs
Invoke-AtomicTest T1059.001 -TestNumbers 1

# Cleanup after test
Invoke-AtomicTest T1059.001 -TestNumbers 1 -Cleanup

Via Attack Range (remote execution)

cd "$ATTACK_RANGE_PATH"
source "$ATTACK_RANGE_VENV/bin/activate"

# Run a standard atomic remotely
python attack_range.py simulate -t T1059.001 --target <TARGET_NAME>

# Run specific test number
python attack_range.py simulate -t T1059.001 -tn 1 --target <TARGET_NAME>

Via Ansible (direct SSH/WinRM)

ansible <TARGET_NAME> -m win_shell -a "Invoke-AtomicTest T1059.001 -TestNumbers 1" \
  --extra-vars "ansible_host=<TARGET_IP>"

Custom Atomics (T9999.XXX)

When no standard atomic exists for your detection scenario, create a custom atomic using the T9999.XXX numbering scheme. This avoids collisions with upstream Atomic Red Team technique IDs.

Numbering Convention

Custom Atomic YAML Structure

attack_technique: T9999.001
display_name: "Custom - Suspicious PowerShell Download Cradle"
atomic_tests:
  - name: "PowerShell download cradle with Net.WebClient"
    auto_generated_guid: <generate-a-uuid>
    description: |
      Simulates a PowerShell download cradle using Net.WebClient.
      Designed to trigger detections for T1059.001 + T1105.
    supported_platforms:
      - windows
    executor:
      command: |
        powershell.exe -NoProfile -Command "(New-Object Net.WebClient).DownloadString('http://127.0.0.1/test')"
      name: command_prompt
      elevation_required: false

Deploying Custom Atomics

1. Place YAML in $CUSTOM_ATOMICS_PATH/T9999.XXX/T9999.XXX.yaml
2. Copy to target's atomics folder or use Ansible:

ansible <TARGET_NAME> -m win_copy \
  -a "src=$CUSTOM_ATOMICS_PATH/T9999.001/ dest=C:\\AtomicRedTeam\\atomics\\T9999.001\\" \
  --extra-vars "ansible_host=<TARGET_IP>"

3. Execute on target:

Invoke-AtomicTest T9999.001 -TestNumbers 1

Validation Workflow

The standard workflow is: Deploy → Execute → Wait → Validate

Step 1: Deploy (if needed)

Ensure the target has Invoke-AtomicRedTeam installed and any custom atomics are synced.

Step 2: Execute

Run the atomic test (see above). Note the exact execution time.

Step 3: Wait for Ingestion

Telemetry takes time to reach your SIEM. Typical delays:

Recommendation: Wait at least 2 minutes before querying, then retry at 5 minutes if nothing appears.

Step 4: Validate

Check for telemetry first, then run the detection. Commands differ by SIEM:

Splunk (SPL):

// Check raw telemetry arrived
index=* sourcetype=* "<expected_process_name>" earliest=-15m

// Run the actual detection search
| your_detection_search_here

Sentinel (KQL):

// Check raw telemetry arrived
DeviceProcessEvents
| where Timestamp > ago(15m)
| where FileName == "<expected_process_name>"

// Or for SecurityEvent-based logs
SecurityEvent
| where TimeGenerated > ago(15m)
| where Process == "<expected_process_name>"

Elastic (EQL in Dev Tools or Discover):

// Check raw telemetry arrived (via Security → Timelines or Discover)
process where process.name == "<expected_process_name>"
  and @timestamp > "now-15m"

Sigma (compile first, then test in target SIEM):

# Compile to your backend
sigma convert -t splunk -p sysmon rule.yml
sigma convert -t microsoft365defender rule.yml
sigma convert -t elasticsearch rule.yml

Decision Tree

Atomic executed
  └─ Telemetry in SIEM? 
       ├─ NO → Check: UF running? Correct sourcetype? Parsing errors?
       └─ YES → Detection fires?
            ├─ NO → Check: Field names? Time window? Logic errors?
            └─ YES → Document result ✓ → Move to next test

Troubleshooting

No telemetry after execution

1. Verify the atomic actually ran — Check exit code and target process list
2. Check forwarder/agent status:
   • Splunk: Universal Forwarder (splunk status)
   • Elastic: Elastic Agent (elastic-agent status)
   • Sentinel: Azure Monitor Agent or MDE sensor health in portal
   • Generic: Winlogbeat/Filebeat (systemctl status filebeat)
3. Check sourcetype/index/table — Events may land in an unexpected location
4. Check time sync — Clock skew between target and SIEM causes missed windows

Atomic fails to execute

1. Prerequisites missing — Run -GetPrereqs first
2. Execution policy — Set-ExecutionPolicy Bypass -Scope Process
3. AV/EDR blocking — May need exclusions for test atomics (document any exclusions!)
4. Elevation required — Some atomics need admin; check elevation_required field

Detection doesn't fire despite telemetry

1. Field mapping mismatch — CIM fields vs raw fields vs ECS fields
2. Time window too narrow — Widen the search window
3. Filter too aggressive — Temporarily remove filters and re-run
4. Threshold not met — Some detections require N events; run atomic multiple times

Custom atomic not found on target

1. Path mismatch — Atomics folder must match Invoke-AtomicRedTeam's expected path
2. YAML syntax — Validate YAML before deploying (yamllint T9999.XXX.yaml)
3. GUID missing — Every test needs a unique auto_generated_guid

Integration with Detection Engineering Workflow

1. Identify coverage gap (technique with no detection)
2. Write detection rule (SPL / Sigma / KQL)
3. Find or create atomic test for the technique
4. Deploy atomic to test environment
5. Execute atomic
6. Validate telemetry arrives
7. Validate detection fires
8. Document results (log_decision in knowledge graph)
9. Submit detection PR with test evidence

This workflow ensures every detection is tested before merge — not just syntactically valid but actually capable of catching the behavior it claims to detect.