Remote File Download via MpCmdRun

## Triage and analysis

### Investigating Remote File Download via MpCmdRun

Attackers commonly transfer tooling or malware from external systems into a compromised environment using the command
and control channel. However, they can also abuse signed utilities to drop these files.

The `MpCmdRun.exe` is a command-line tool part of Windows Defender and is used to manage various Microsoft Windows
Defender Antivirus settings and perform certain tasks. It can also be abused by attackers to download remote files,
including malware and offensive tooling. This rule looks for the patterns used to perform downloads using the utility.

#### Possible investigation steps

- Investigate the process execution chain (parent process tree).
- Identify the user account that performed the action and whether it should perform this kind of action.
- Contact the account owner and confirm whether they are aware of this activity.
- Investigate other alerts associated with the user/host during the past 48 hours.
- Check the reputation of the domain or IP address used to host the downloaded file.
- Retrieve the file and determine if it is malicious:
  - Use a private sandboxed malware analysis system to perform analysis.
    - Observe and collect information about the following activities:
      - Attempts to contact external domains and addresses.
      - File and registry access, modification, and creation activities.
      - Service creation and launch activities.
      - Scheduled tasks creation.
  - Use the PowerShell Get-FileHash cmdlet to get the SHA-256 hash value of the file.
    - Search for the existence and reputation of this file in resources like VirusTotal, Hybrid-Analysis, CISCO Talos, Any.run, etc.

### False positive analysis

- This activity is unlikely to happen legitimately. Benign true positives (B-TPs) can be added as exceptions if necessary.

### Response and remediation

- Initiate the incident response process based on the outcome of the triage.
- Isolate the involved host to prevent further post-compromise behavior.
- If the triage identified malware, search the environment for additional compromised hosts.
  - Implement any temporary network rules, procedures, and segmentation required to contain the malware.
  - Immediately block the IoCs identified.
- Remove and block malicious artifacts identified on the triage.
- Disable the involved accounts, or restrict their ability to log on remotely.
- Reset passwords for the user account and other potentially compromised accounts (email, services, CRMs, etc.).
- Investigate the initial attack vector.
Verify details such as the parent process, URL reputation, and downloaded file details. Additionally, `MpCmdRun` logs this information in the Appdata Temp folder in `MpCmdRun.log`.


## Config

If enabling an EQL rule on a non-elastic-agent index (such as beats) for versions <8.2, events will not define `event.ingested` and default fallback for EQL rules was not added until 8.2, so you will need to add a custom pipeline to populate `event.ingested` to @timestamp for this rule to work.