Unusual File Modification by dns.exe

Status: test
Severity: high
Log source: category file_change, product windows
Author: Tim Rauch (Nextron Systems), Elastic (idea)
Source: github.com/SigmaHQ/sigma

Detects an unexpected file being modified by dns.exe which my indicate activity related to remote code execution or other forms of exploitation as seen in CVE-2020-1350 (SigRed)

MITRE ATT&CK coverage

Tactic	Techniques
Initial Access	`T1133` External Remote Services
Persistence	`T1133` External Remote Services

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 2: A process changed a file creation time

Rule body

title: Unusual File Modification by dns.exe
id: 9f383dc0-fdeb-4d56-acbc-9f9f4f8f20f3
related:
    - id: 8f0b1fb1-9bd4-4e74-8cdf-a8de4d2adfd0 # FileDelete version
      type: similar
status: test
description: Detects an unexpected file being modified by dns.exe which my indicate activity related to remote code execution or other forms of exploitation as seen in CVE-2020-1350 (SigRed)
references:
    - https://www.elastic.co/guide/en/security/current/unusual-file-modification-by-dns-exe.html
author: Tim Rauch (Nextron Systems), Elastic (idea)
date: 2022-09-27
tags:
    - attack.persistence
    - attack.initial-access
    - attack.t1133
logsource:
    category: file_change
    product: windows
detection:
    selection:
        Image|endswith: '\dns.exe'
    filter:
        TargetFilename|endswith: '\dns.log'
    condition: selection and not filter
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

selection and not filter

Stage 1: `selection`

selection:
    Image|endswith: '\dns.exe'

Stage 2: `not filter`

filter:
    TargetFilename|endswith: '\dns.log'

Exclusions

The rule actively suppresses these predicates.

Field	Kind	Excluded values	Search
`TargetFilename`	ends_with	`\dns.log`	`excludes:TargetFilename` `field:"TargetFilename" value:"\dns.log"`

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`Image`	ends_with	`\dns.exe` corpus 2 (sigma 2)	`field:"Image" kind:ends_with value:"\dns.exe"`