Triage and analysis

Investigating Unusual File Write

Detection alerts from this rule indicate potential unusual/abnormal file writes from the DNS Server service process (dns.exe) after exploitation from CVE-2020-1350 (SigRed) has occurred. Here are some possible avenues of investigation: - Post-exploitation, adversaries may write additional files or payloads to the system as additional discovery/exploitation/persistence mechanisms. - Any suspicious or abnormal files written from dns.exe should be reviewed and investigated with care.

Setup

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 version 8.2. Hence for this rule to work effectively, users will need to add a custom ingest pipeline to populate event.ingested to @timestamp. For more details on adding a custom ingest pipeline refer - https://www.elastic.co/guide/en/fleet/current/data-streams-pipeline-tutorial.html

file where host.os.type == "windows" and process.name : "dns.exe" and event.type in ("creation", "deletion", "change") and
  not file.name : "dns.log" and not
  (file.extension : ("old", "temp", "bak", "dns", "arpa") and file.path : "C:\\Windows\\System32\\dns\\*")

Framework: MITRE ATT&CK^TM