DNS RCE CVE-2020-1350

Status: test
Severity: critical
Log source: category process_creation, product windows
Author: Florian Roth (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects exploitation of DNS RCE bug reported in CVE-2020-1350 by the detection of suspicious sub process

Known false positives

Unknown but benign sub processes of the Windows DNS service dns.exe

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1190` Exploit Public-Facing Application
Execution	`T1569.002` System Services: Service Execution

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

title: DNS RCE CVE-2020-1350
id: b5281f31-f9cc-4d0d-95d0-45b91c45b487
status: test
description: Detects exploitation of DNS RCE bug reported in CVE-2020-1350 by the detection of suspicious sub process
references:
    - https://research.checkpoint.com/2020/resolving-your-way-into-domain-admin-exploiting-a-17-year-old-bug-in-windows-dns-servers/
    - https://web.archive.org/web/20230329172447/https://blog.menasec.net/2019/02/threat-hunting-24-microsoft-windows-dns.html
author: Florian Roth (Nextron Systems)
date: 2020-07-15
modified: 2022-07-12
tags:
    - attack.initial-access
    - attack.t1190
    - attack.execution
    - attack.t1569.002
    - cve.2020-1350
    - detection.emerging-threats
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        ParentImage|endswith: '\System32\dns.exe'
    filter:
        Image|endswith:
            - '\System32\werfault.exe'
            - '\System32\conhost.exe'
            - '\System32\dnscmd.exe'
            - '\System32\dns.exe'
    condition: selection and not filter
falsepositives:
    - Unknown but benign sub processes of the Windows DNS service dns.exe
level: critical

Stages and Predicates

Stage 0: `condition`

selection and not filter

Stage 1: `selection`

selection:
    ParentImage|endswith: '\System32\dns.exe'

Stage 2: `not filter`

filter:
    Image|endswith:
        - '\System32\werfault.exe'
        - '\System32\conhost.exe'
        - '\System32\dnscmd.exe'
        - '\System32\dns.exe'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`Image`	ends_with	`\System32\conhost.exe`	`excludes:Image` `field:"Image" value:"\System32\conhost.exe"`
`Image`	ends_with	`\System32\dns.exe`	`excludes:Image` `field:"Image" value:"\System32\dns.exe"`
`Image`	ends_with	`\System32\dnscmd.exe`	`excludes:Image` `field:"Image" value:"\System32\dnscmd.exe"`
`Image`	ends_with	`\System32\werfault.exe`	`excludes:Image` `field:"Image" value:"\System32\werfault.exe"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`ParentImage`	ends_with	`\System32\dns.exe`	`field:"ParentImage" kind:ends_with value:"\System32\dns.exe"`