Unusual File Modification by dns.exe

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.*
logs-windows.*

Severity: high

Risk score: 73

Runs every: 5 minutes

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

Maximum alerts per execution: 100

References:

Tags:

Elastic
Host
Windows
Threat Detection
Initial Access

Version: 5 (version history)

Added (Elastic Stack release): 7.10.0

Last modified (Elastic Stack release): 7.13.0

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.

Rule query

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file where process.name : "dns.exe" and event.type in ("creation",
"deletion", "change") and not file.name : "dns.log"

Threat mapping

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Framework: MITRE ATT&CK^TM

Tactic:
- Name: Initial Access
- ID: TA0001
- Reference URL: https://attack.mitre.org/tactics/TA0001/
Technique:
- Name: External Remote Services
- ID: T1133
- Reference URL: https://attack.mitre.org/techniques/T1133/

Rule version history

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Version 5 (7.13.0 release)

Updated query, changed from:

event.category:file and process.name:dns.exe and event.type:(creation
or deletion or change) and not file.name:dns.log

Version 4 (7.12.0 release)

Formatting only

Version 3 (7.11.2 release)

Formatting only

Version 2 (7.11.0 release)

Updated query, changed from:

event.category:file and process.name:dns.exe and not file.name:dns.log

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