IcedID Malware Suspicious Single Digit DLL Execution Via Rundll32

Status: test
Severity: high
Log source: category process_creation, product windows
Author: Nasreddine Bencherchali (Nextron Systems)
Source: github.com/SigmaHQ/sigma

Detects RunDLL32.exe executing a single digit DLL named "1.dll" with the export function "DllRegisterServer". This behaviour was often seen used by malware and especially IcedID

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
Security-Auditing	Event ID 4688: A new process has been created.

Rule body

title: IcedID Malware Suspicious Single Digit DLL Execution Via Rundll32
id: 2bd8e100-5b3b-4b6a-bbb5-b129d3ddddc5
status: test
description: Detects RunDLL32.exe executing a single digit DLL named "1.dll" with the export function "DllRegisterServer". This behaviour was often seen used by malware and especially IcedID
references:
    - https://thedfirreport.com/2023/05/22/icedid-macro-ends-in-nokoyawa-ransomware/
    - https://thedfirreport.com/2023/08/28/html-smuggling-leads-to-domain-wide-ransomware/
author: Nasreddine Bencherchali (Nextron Systems)
date: 2023-08-31
tags:
    - attack.stealth
    - attack.t1218.011
    - detection.emerging-threats
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\rundll32.exe'
        CommandLine|endswith:
            - '\1.dll, DllRegisterServer' # In case of full path exec
            - ' 1.dll, DllRegisterServer' # In case of direct exec
    condition: selection
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: `condition`

selection

Stage 1: `selection`

selection:
    Image|endswith: '\rundll32.exe'
    CommandLine|endswith:
        - '\1.dll, DllRegisterServer'
        - ' 1.dll, DllRegisterServer'

Indicators

These rows show field, operator, and value matches.

Field	Kind	Values	Search
`CommandLine`	ends_with	`1.dll, DllRegisterServer` `\1.dll, DllRegisterServer`	`field:"CommandLine" kind:ends_with`
`Image`	ends_with	`\rundll32.exe` corpus 94 (sigma 94)	`field:"Image" kind:ends_with value:"\rundll32.exe"`