Unusual File Modification by dns.exe

Elastic Stack Serverless Security

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 (https://www.elastic.co/guide/en/elasticsearch/reference/current/common-options.html#date-math[Date Math format], see also Additional look-back time)

Maximum alerts per execution: 100

References:

• https://research.checkpoint.com/2020/resolving-your-way-into-domain-admin-exploiting-a-17-year-old-bug-in-windows-dns-servers/
• https://msrc-blog.microsoft.com/2020/07/14/july-2020-security-update-cve-2020-1350-vulnerability-in-windows-domain-name-system-dns-server/
• https://www.elastic.co/security-labs/detection-rules-for-sigred-vulnerability

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
• Resources: Investigation Guide

Version: 212

Rule authors:

• Elastic

Rule license: Elastic License v2

Triage and analysis

Investigating Unusual File Modification by dns.exe

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.

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\\*") and

  /* DNS logs with custom names, header converts to "DNS Server log" */
  not ?file.Ext.header_bytes : "444e5320536572766572206c6f67*"

Framework: MITRE ATT&CKTM

• Tactic:

  • Name: Lateral Movement
  • ID: TA0008
  • Reference URL: https://attack.mitre.org/tactics/TA0008/

• Technique:

  • Name: Exploitation of Remote Services
  • ID: T1210
  • Reference URL: https://attack.mitre.org/techniques/T1210/