Signed Binary Proxy Execution

Overview

Signed Binary Proxy Execution is a technique where adversaries leverage digitally signed, trusted binaries to execute malicious code indirectly. This approach allows attackers to bypass security controls by using legitimate system or third-party signed executables as proxies, facilitating stealthy execution during various stages of an attack.

Attack Objective

• Evade detection and maintain stealth during code execution
• Supports multiple stages including Execution, Persistence, Privilege Escalation, and Defense Evasion
• Advances attacker position by exploiting trusted binaries to run unauthorized code without triggering security alerts

How the Technique Works

Adversaries identify signed binaries that are permitted to execute on a system and use them as intermediaries to run malicious payloads. These signed binaries act as proxies, invoking or loading attacker-controlled code in a manner that appears legitimate to security mechanisms, thereby circumventing application whitelisting, endpoint detection, and other defenses.

Common Methods & Variations

• Utilizing signed system utilities or third-party applications with proxy execution capabilities
• Variants observed on endpoints, cloud environments, and identity platforms where signed binaries are present
• Predominantly living-off-the-land techniques leveraging existing signed binaries rather than deploying custom malware

Indicators of Compromise (IOCs)

• Unusual invocation of signed binaries with uncommon command-line arguments or parent-child process relationships
• Execution of signed binaries from non-standard directories or by unexpected users
• Endpoint logs showing anomalous process spawning involving trusted signed executables

Detection Strategies

• Monitoring process creation events and command-line arguments through endpoint detection and response (EDR) telemetry
• Behavioral detection focusing on anomalous use of signed binaries rather than relying solely on signature-based methods
• Correlation of process lineage and user activity to identify deviations from normal patterns

Mitigation & Prevention

• Implement application control policies restricting execution of signed binaries to known and necessary use cases
• Enforce least privilege principles to limit user ability to invoke proxy binaries
• Regularly audit and update allowlists to exclude signed binaries that can be abused for proxy execution

Response Considerations

• Contain affected systems by terminating suspicious processes involving signed binaries
• Investigate process trees and command-line arguments to determine scope and impact
• Harden environment by reviewing and tightening execution policies and monitoring for recurrence

Related Techniques

• Living off the Land Binaries (LOLBins)
• Process Injection
• Bypass User Account Control (UAC)
• Signed Script Proxy Execution

Mapping & References

• MITRE ATT&CK: T1218 – Signed Binary Proxy Execution
• Public research on LOLBins and proxy execution techniques from cybersecurity vendors and incident reports