Regsvr32
Regsvr32 [T1218.010]
Information
Introduction
Regsvr32 (T1218.010) is a sub-technique within the MITRE ATT&CK framework under the broader category of "Signed Binary Proxy Execution." Attackers leverage Regsvr32, a legitimate Windows command-line utility, to execute arbitrary code, bypass application whitelisting, and evade detection by security mechanisms. Regsvr32 is primarily designed to register and unregister Object Linking and Embedding (OLE) controls, such as DLL files, in the Windows registry. However, adversaries abuse this legitimate functionality to execute malicious scripts without directly calling suspicious binaries or executables.
Deep Dive Into Technique
Regsvr32 is a legitimate Windows utility typically located at %SystemRoot%\System32\regsvr32.exe. It is designed to register and unregister DLL files and ActiveX controls into the Windows registry, enabling their use by other applications. Attackers exploit Regsvr32's built-in capability to execute scripts remotely or locally, making it a powerful tool for circumventing security controls.
Technical details include:
Execution Method:
Attackers use the
/ioption to specify a DLL or script file.The
/sswitch can be used to suppress error messages and dialogs, making execution stealthy.Regsvr32 can be instructed to download and execute scripts directly from remote URLs, allowing attackers to host malicious payloads externally.
Example Command Syntax:
Explanation of parameters:
/s: Silent mode, suppresses error messages./u: Unregisters the DLL; in combination with/i, it allows execution without actual registration./i: Specifies the script or DLL to execute.scrobj.dll: Microsoft’s script component runtime DLL, commonly used by attackers to execute scriptlets (.sct files).
Mechanisms and Real-World Procedures:
Attackers commonly host malicious COM scriptlets (.sct files) remotely to bypass local detection.
Payloads executed via Regsvr32 can include malware downloaders, reverse shells, or other malicious scripts.
The technique leverages legitimate Windows binaries ("living off the land") to evade endpoint security tools.
When this Technique is Usually Used
Attackers commonly leverage Regsvr32 (T1218.010) in various stages of the cyberattack lifecycle, including:
Initial Access and Execution:
Phishing campaigns delivering malicious scripts or documents that invoke Regsvr32 commands.
Drive-by download attacks where users inadvertently execute scripts that invoke Regsvr32.
Defense Evasion:
Bypassing application whitelisting and execution policies, as Regsvr32 is typically allowed by default.
Evading detection by leveraging legitimate Windows utilities rather than suspicious executables.
Persistence and Lateral Movement:
Attackers may use Regsvr32 commands within scheduled tasks or registry keys for persistent execution.
Leveraged during lateral movement to execute code remotely across compromised systems.
How this Technique is Usually Detected
Detecting the misuse of Regsvr32 involves monitoring and logging its execution patterns and behaviors. Effective detection methods include:
Command Line Monitoring:
Implementing endpoint detection and response (EDR) tools to monitor and analyze command-line arguments passed to
regsvr32.exe.Detecting suspicious parameters such as
/u,/i, and remote URLs in command execution.
Process Monitoring and Behavioral Analysis:
Monitoring parent-child process relationships involving
regsvr32.exe.Alerting on unusual network connections initiated by Regsvr32, especially to external IP addresses or domains.
Network Traffic Analysis:
Monitoring outbound HTTP/HTTPS connections initiated by Regsvr32 to external URLs.
Identifying downloads of scriptlets (.sct files) or DLL files from suspicious or uncategorized domains.
Indicators of Compromise (IoCs):
Suspicious command-line parameters involving remote URLs (e.g.,
/i:http://).Unusual scriptlet (.sct) files or DLLs hosted remotely.
Unexpected network requests from Regsvr32 to external IP addresses or domains.
Why it is Important to Detect This Technique
Early detection of Regsvr32 misuse is critical due to its potential impacts on systems and networks, including:
Bypassing Security Controls:
Attackers exploit trusted system utilities, circumventing traditional antivirus, application whitelisting, and endpoint security solutions.
Enabling Malware Delivery and Execution:
Allows attackers to download and execute malicious payloads remotely, facilitating further compromise, data exfiltration, or ransomware deployment.
Persistence and Stealth:
Attackers may establish persistent footholds, making detection and remediation significantly more challenging.
Abuse of legitimate binaries reduces the likelihood of detection, prolonging attacker dwell time and increasing potential damage.
Potential for Rapid Lateral Movement:
Regsvr32 abuse can facilitate lateral movement across internal networks, increasing the scope and severity of a breach.
Examples
Real-world examples of Regsvr32 misuse include:
APT32 (OceanLotus):
Utilized Regsvr32 to execute remote scriptlets hosted on attacker-controlled servers, bypassing endpoint protections.
Delivered malicious payloads to targeted organizations in Southeast Asia.
FIN7 Cybercrime Group:
Used Regsvr32 commands embedded in malicious documents or scripts to download and execute payloads, enabling initial access and subsequent lateral movement within victim environments.
PowerDuke Malware Campaign:
Leveraged Regsvr32 to execute scriptlets (.sct files) hosted remotely, enabling stealthy malware delivery and execution on targeted systems.
"Squiblydoo" Technique:
Publicly documented by security researcher Casey Smith, demonstrating how attackers could abuse Regsvr32 to execute malicious scripts remotely, bypassing application whitelisting and endpoint security solutions.
In these examples, attackers exploited legitimate Windows utilities to evade detection, execute malicious payloads, and establish persistent access within victim environments.
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