Rundll32
Rundll32 [T1218.011]
Information
Introduction
Rundll32 (T1218.011) is a sub-technique within the MITRE ATT&CK framework categorized under Signed Binary Proxy Execution. Attackers leverage the legitimate Windows executable "rundll32.exe" to execute malicious code or payloads. Rundll32.exe is a standard Windows utility designed to load and execute dynamic link libraries (DLLs), making it an attractive target for adversaries aiming to bypass security defenses and execute arbitrary code while appearing legitimate.
Deep Dive Into Technique
The Windows utility "rundll32.exe" is designed to execute functions exported from DLL files. Its legitimate purpose is to allow users and applications to invoke specific DLL functions directly from the command line or scripts. Attackers abuse this functionality by crafting malicious DLLs or referencing legitimate DLLs that contain exploitable or unintended functions.
Technical details include:
Command syntax typically used by attackers:
Malicious DLLs may contain exported functions specifically crafted for exploitation and payload delivery.
Attackers may also exploit legitimate system DLLs by invoking functions that can execute arbitrary code or scripts.
Rundll32 can be used to execute payloads directly from disk, memory, or remote locations, providing attackers with a flexible execution vector.
Commonly abused legitimate DLLs include:
shell32.dllurl.dlladvpack.dllieadvpack.dll
Real-world procedures include:
Execution of malicious payloads stored remotely via URL:
Execution of DLLs loaded directly from disk:
Execution of payloads stored in the registry or encoded within scripts.
When this Technique is Usually Used
Attack scenarios and stages where attackers typically leverage Rundll32 include:
Initial Access and Execution:
Delivering initial payloads after successful phishing attacks or drive-by downloads.
Executing payloads immediately following exploitation of vulnerabilities.
Defense Evasion and Persistence:
Bypassing application allowlisting, endpoint protection, and antivirus software by masquerading as legitimate system activity.
Establishing persistence through registry modifications or scheduled tasks invoking rundll32 commands.
Privilege Escalation and Lateral Movement:
Executing DLL payloads that exploit system vulnerabilities or misconfigurations to escalate privileges.
Facilitating lateral movement by executing payloads remotely on compromised hosts.
Command and Control (C2) and Exfiltration:
Executing payloads designed to establish persistent communication channels to attacker-controlled servers.
Running DLLs that facilitate data exfiltration or remote access.
How this Technique is Usually Detected
Effective detection of Rundll32 misuse involves monitoring and analyzing process execution patterns, command-line arguments, and DLL loading behaviors. Detection methods include:
Process Monitoring and Analysis:
Monitor the execution of "rundll32.exe" processes, especially those initiated from unusual parent processes, locations, or user contexts.
Analyze command-line arguments for suspicious DLL names, functions, or remote URLs.
DLL Loading Behavior:
Monitor DLL loads by rundll32.exe, particularly those from temporary directories, user directories, or unusual paths.
Track DLLs loaded from remote locations or network shares.
Endpoint Detection and Response (EDR) Tools:
Utilize EDR solutions to detect anomalous rundll32.exe behavior, including suspicious command-line parameters and unusual DLL loads.
EDR platforms such as Microsoft Defender ATP, CrowdStrike Falcon, Carbon Black, and SentinelOne provide built-in detection rules for suspicious rundll32 activity.
Security Information and Event Management (SIEM):
Aggregate and correlate logs from endpoints and network devices to identify anomalous rundll32 executions.
Create alerts and rules based on known suspicious rundll32 command-line patterns or DLL execution paths.
Indicators of Compromise (IoCs):
Unusual rundll32.exe command-line arguments referencing suspicious DLL files or URLs.
DLL files located in temporary directories, user profiles, or unusual system locations.
Registry entries or scheduled tasks invoking rundll32.exe with suspicious parameters.
Why it is Important to Detect This Technique
Detecting the misuse of rundll32.exe is critical due to its potential impact on systems and networks:
Stealth and Defense Evasion:
Attackers exploit legitimate system binaries to avoid detection by traditional antivirus and endpoint protection tools.
Rundll32 misuse can bypass application allowlisting and evade security controls, increasing the likelihood of successful compromise.
Persistence and Long-Term Access:
Misuse of rundll32.exe can enable attackers to establish persistent footholds on compromised systems, making remediation challenging.
Persistent malicious DLL execution can lead to prolonged attacker presence and continued exploitation.
Privilege Escalation and Lateral Movement:
Malicious DLL payloads executed via rundll32 can facilitate privilege escalation, lateral movement, and deeper network compromise.
Early detection prevents attackers from expanding their access and escalating privileges.
Data Theft and Exfiltration:
Payloads executed through rundll32.exe can enable attackers to exfiltrate sensitive information, intellectual property, and credentials.
Early detection and mitigation reduce the risk of significant data breaches and associated damages.
Examples
Real-world examples highlighting the misuse of rundll32.exe include:
APT29 (Cozy Bear):
Utilized rundll32.exe to execute malicious DLL payloads during the initial compromise and persistence phases.
Leveraged rundll32 commands to load DLLs from disk, enabling stealthy execution and evasion of endpoint protection.
FIN7 Cybercrime Group:
Employed rundll32.exe to execute malicious payloads downloaded from remote servers as part of targeted attacks against financial institutions and retail organizations.
Used rundll32.exe commands referencing URLs to execute DLL payloads directly from remote attacker-controlled servers.
Qbot Malware:
Frequently leverages rundll32.exe to execute malicious DLL payloads stored in user directories or temporary folders.
Executes payloads via command-line parameters referencing malicious DLL entry points, enabling persistence and data exfiltration.
TrickBot Malware:
Utilizes rundll32.exe extensively to execute malicious DLL payloads during initial infection and lateral movement phases.
Executes malicious DLLs from unusual locations, such as AppData directories, to evade detection and establish persistence.
These examples illustrate the widespread use of rundll32.exe misuse across diverse threat actors and malware families. Detecting and mitigating this technique is critical for defending against advanced persistent threats (APTs), cybercriminal groups, and malware infections.
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