Unusual Child Process of dns.exe

## Triage and analysis

### Investigating Unusual Child Process
Detection alerts from this rule indicate potential suspicious child processes spawned after exploitation from CVE-2020-1350 (SigRed) has occurred. Here are some possible avenues of investigation:
- Any suspicious or abnormal child process spawned from dns.exe should be reviewed and investigated with care. It's impossible to predict what an adversary may deploy as the follow-on process after the exploit, but built-in discovery/enumeration utilities should be top of mind (whoami.exe, netstat.exe, systeminfo.exe, tasklist.exe).
- Built-in Windows programs that contain capabilities used to download and execute additional payloads should also be considered. This is not an exhaustive list, but ideal candidates to start out would be: mshta.exe, powershell.exe, regsvr32.exe, rundll32.exe, wscript.exe, wmic.exe.
- If the DoS exploit is successful and DNS Server service crashes, be mindful of potential child processes related to werfault.exe occurring.
- Any subsequent activity following the child process spawned related to execution/network activity should be thoroughly reviewed from the endpoint.

## 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.