Unusual Network Connection via RunDLL32

Last updated 6 days ago on 2025-08-12
Created 6 years ago on 2020-02-18

About

Identifies unusual instances of rundll32.exe making outbound network connections. This may indicate adversarial Command and Control activity.
Tags
Domain: EndpointOS: WindowsUse Case: Threat DetectionTactic: Defense EvasionTactic: Command and ControlData Source: Elastic DefendData Source: SysmonLanguage: eql
Severity
medium
Risk Score
47
MITRE ATT&CK™

Defense Evasion (TA0005)(opens in a new tab or window)

Command and Control (TA0011)(opens in a new tab or window)

License
Elastic License v2(opens in a new tab or window)

Definition

Rule Type
Event Correlation Rule
Integration Pack
Prebuilt Security Detection Rules
Index Patterns
winlogbeat-*logs-endpoint.events.process-*logs-endpoint.events.network-*logs-windows.sysmon_operational-*
Related Integrations

endpoint(opens in a new tab or window)

windows(opens in a new tab or window)

Query
sequence by host.id, process.entity_id with maxspan=1m
  [process where host.os.type == "windows" and event.type == "start" and process.name : "rundll32.exe" and
  (
    process.args_count == 1 and

    /* Excludes bug where a missing closing quote sets args_count to 1 despite extra args */
    not process.command_line regex~ """\".*\.exe[^\"].*"""
  )]
  [network where host.os.type == "windows" and process.name : "rundll32.exe" and
   not cidrmatch(destination.ip, "10.0.0.0/8", "127.0.0.0/8", "169.254.0.0/16", "172.16.0.0/12", "192.0.0.0/24",
       "192.0.0.0/29", "192.0.0.8/32", "192.0.0.9/32", "192.0.0.10/32", "192.0.0.170/32", "192.0.0.171/32",
       "192.0.2.0/24", "192.31.196.0/24", "192.52.193.0/24", "192.168.0.0/16", "192.88.99.0/24", "224.0.0.0/4",
       "100.64.0.0/10", "192.175.48.0/24","198.18.0.0/15", "198.51.100.0/24", "203.0.113.0/24", "240.0.0.0/4", "::1",
       "FE80::/10", "FF00::/8")]

Install detection rules in Elastic Security

Detect Unusual Network Connection via RunDLL32 in the Elastic Security detection engine by installing this rule into your Elastic Stack.

To setup this rule, check out the installation guide for Prebuilt Security Detection Rules(opens in a new tab or window).