Suspicious Rundll32 Execution With Image Extension

Status: test
Severity: high
Log source: category process_creation, product windows
Author: Hieu Tran
Source: github.com/SigmaHQ/sigma

Detects the execution of Rundll32.exe with DLL files masquerading as image files

MITRE ATT&CK coverage

Tactic	Techniques
Stealth	`T1218.011` System Binary Proxy Execution: Rundll32

Telemetry coverage

Provider	Record / event type
Sysmon	Event ID 1: Process creation

Rule body

title: Suspicious Rundll32 Execution With Image Extension
id: 4aa6040b-3f28-44e3-a769-9208e5feb5ec
related:
    - id: 089fc3d2-71e8-4763-a8a5-c97fbb0a403e
      type: similar
status: test
description: Detects the execution of Rundll32.exe with DLL files masquerading as image files
references:
    - https://www.zscaler.com/blogs/security-research/onenote-growing-threat-malware-distribution
author: Hieu Tran
date: 2023-03-13
tags:
    - attack.stealth
    - attack.t1218.011
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith: '\rundll32.exe'
        - OriginalFileName: 'RUNDLL32.exe'
    selection_cli:
        CommandLine|contains:
            - '.bmp'
            - '.cr2'
            - '.eps'
            - '.gif'
            - '.ico'
            - '.jpeg'
            - '.jpg'
            - '.nef'
            - '.orf'
            - '.png'
            - '.raw'
            - '.sr2'
            - '.tif'
            - '.tiff'
    condition: all of selection_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

all of selection_*

Stage 1: `selection_img`

selection_img:
    - Image|endswith: '\rundll32.exe'
    - OriginalFileName: 'RUNDLL32.exe'

Stage 2: `selection_cli`

selection_cli:
    CommandLine|contains:
        - '.bmp'
        - '.cr2'
        - '.eps'
        - '.gif'
        - '.ico'
        - '.jpeg'
        - '.jpg'
        - '.nef'
        - '.orf'
        - '.png'
        - '.raw'
        - '.sr2'
        - '.tif'
        - '.tiff'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	match	`.bmp` corpus 3 (sigma 2, elastic 1) `.cr2` `.eps` `.gif` corpus 9 (sigma 8, elastic 1) `.ico` `.jpeg` corpus 7 (sigma 6, elastic 1) `.jpg` corpus 8 (sigma 7, elastic 1) `.nef` `.orf` `.png` corpus 8 (sigma 7, elastic 1) `.raw` `.sr2` `.tif` `.tiff` corpus 2 (sigma 1, elastic 1)	`field:"CommandLine" kind:match`
`Image`	ends_with	`\rundll32.exe` corpus 94 (sigma 94)	`field:"Image" kind:ends_with value:"\rundll32.exe"`
`OriginalFileName`	eq	`RUNDLL32.exe` corpus 78 (sigma 35, elastic 22, splunk 21)	`field:"OriginalFileName" kind:eq value:"RUNDLL32.exe"`

Suspicious Rundll32 Execution With Image Extension

MITRE ATT&CK coverage

Telemetry coverage

Rule body

Stages and Predicates

Stage 0: condition

Stage 1: selection_img

Stage 2: selection_cli

Indicators

Stage 0: `condition`

Stage 1: `selection_img`

Stage 2: `selection_cli`