Google Chrome DLL Side Loading Exploit: A Deep Dive into Emerging Cyber Threats

Executive Summary

Threat actors are actively exploiting a vulnerability in Google Chrome version 133.0.6943.126 by leveraging DLL side-loading techniques to execute malicious code through a trusted subprocess. This attack vector has been commercialized on dark web forums, providing detailed implementation instructions for cybercriminals. The exploit involves replacing the legitimate chrome_elf.dll file with a malicious counterpart, enabling multi-stage attacks that include process injection, stealth mechanisms, and persistence techniques.
Alarmingly, detection rates are extremely low—with security tools identifying the malicious DLL in only 2 out of 70 scans while the legitimate Chrome executable remains undetected. The malware is built using the Nim programming language, a rare choice that allows it to bypass conventional signature-based detection mechanisms. The attack allows persistent system access even after the browser is closed, posing a severe long-term security threat.

Understanding DLL Side-Loading

DLL Side-Loading is a widely exploited technique in which a threat actor places a malicious DLL file in a directory where a legitimate application expects to find a trusted DLL. When the application loads the compromised DLL, it unknowingly executes malicious code under the guise of a trusted process.
In this case, attackers are targeting Google Chrome’s chrome_elf.dll to load their payloads stealthily, ensuring continued execution even after Chrome is seemingly terminated. The malware exploits Chrome’s GetInstallDetailsPayload function, which normally handles installation and update tasks, but in the malicious version, it leverages Windows APIs for code injection.

Technical Breakdown of the Chrome DLL Side-Loading Attack

1. Attack Execution

Target: chrome_elf.dll in Google Chrome v133.0.6943.126
Execution Method: The attack starts when the user runs a seemingly legitimate Chrome process, which loads the modified chrome_elf.dll.
Persistence: Even if Chrome is closed, the malware continues running in the background.
Process Injection: The malware launches secondary processes, replacing innocuous applications like Calculator with malicious payloads.

2. Evasion Techniques

Low Detection Rates: The manipulated chrome_elf.dll has a 2/70 detection rate, making it virtually invisible to traditional security tools.
Nim-based Malware Development: Attackers use Nim, a relatively uncommon programming language, to evade signature-based detection methods.
Anti-VM and Anti-Sandbox Techniques: The malware terminates execution if it detects a virtualized or sandboxed environment.
Debugger Detection Evasion: The injected code actively checks for debugging attempts and modifies execution behavior accordingly.

3. Malicious Code Execution

The altered chrome_elf.dll file includes several suspicious functions, particularly within FUN_339029ac0, FUN_33902c990, and FUN_339034f50, which:

Dynamically load system APIs such as GetThreadContext, HeapAlloc, and CreateThread.
Enable covert process injection for malicious code execution.
Utilize memory manipulation tactics (memcpy calls) to stealthily load and execute shellcode.
Implement anti-debugging and anti-reversing techniques by checking system flags and debugging indicators.

Mitigation Strategies

1. Hardening Chrome and System Configurations

Block Vulnerable Chrome Versions: Restrict installations of Google Chrome v133.0.6943.126 via software inventory controls.
Enable DLL Whitelisting: Configure Application Control policies to prevent unauthorized DLL loading.
Use Hash Verification: Implement integrity checks for Chrome executables and DLLs.

2. Strengthening Endpoint Security

Deploy Endpoint Detection and Response (EDR) Solutions: Advanced EDR tools can detect and block DLL Side-Loading techniques.
Use Zero Trust Security Models: Enforce strict access control policies for system processes.
Set Up Process Monitoring Alerts: Detect Chrome processes persisting in the background after the browser is closed.

3. Threat Intelligence and Awareness

Subscribe to Threat Intelligence Feeds: Stay updated on new malware strains exploiting DLL Side-Loading.
Educate Employees on Cybersecurity Risks: Raise awareness about social engineering, phishing, and unauthorized software installations.

Threat Intelligence Indicators (IOCs)

SHA256 Hashes of Malicious DLLs

9b5c56d95298d8863fe346ea99605aa4729f27ec5dd195fe7d5eda32fbf80ca4
a6205a7e4579222a0c5728f9e0bb9fa108344d970b2cf1722873d21e6fa1f802

Conclusion

The exploitation of Google Chrome DLL Side-Loading presents a severe cybersecurity threat, demonstrating how legitimate applications can be leveraged to execute stealthy, persistent malware. This case underscores the necessity for organizations to proactively monitor attack surfaces, implement advanced endpoint defenses, and stay updated with real-time threat intelligence.

ThreatMon will continue to track and analyze emerging cyber threats, providing actionable intelligence to help organizations strengthen their security posture.

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