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Elastic Docs ›Elastic Security Solution [8.13] ›Downloadable rule update v8.13.3

Unusual File Modification by dns.exe

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Unusual File Modification by dns.exe

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Identifies an unexpected file being modified by dns.exe, the process responsible for Windows DNS Server services, which may indicate activity related to remote code execution or other forms of exploitation.

Rule type: eql

Rule indices:

  • winlogbeat-*
  • logs-endpoint.events.file-*
  • logs-windows.sysmon_operational-*
  • endgame-*

Severity: high

Risk score: 73

Runs every: 5m

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

  • Domain: Endpoint
  • OS: Windows
  • Use Case: Threat Detection
  • Tactic: Lateral Movement
  • Data Source: Elastic Endgame
  • Use Case: Vulnerability
  • Data Source: Elastic Defend
  • Data Source: Sysmon

Version: 110

Rule authors:

  • Elastic

Rule license: Elastic License v2

Investigation guide

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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

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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

Rule query

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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&CKTM

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