A new sophisticated cyberattack method has emerged, using DLL side-loading to distribute malicious Python code. This method exploits the DLL search order in Windows to load malicious files in place of legitimate libraries. The attackers target trusted applications, making it harder for security measures to detect the malware. Once the malicious DLL is loaded, it injects Python code into memory, allowing attackers to maintain persistent access to compromised systems.
The attack starts with spear-phishing emails containing seemingly harmless attachments. When opened, the attachment executes a legitimate application, which attempts to load a DLL. The attackers place their malicious DLL higher in the search path, ensuring it gets loaded first. Once this happens, the malware takes control, injecting a Python interpreter into memory and executing the hidden payload. This method allows the malware to operate stealthily and persistently.
The attackers use a custom XOR encryption algorithm to obfuscate the embedded Python code, ensuring it goes undetected.
The Python code is loaded into the system’s memory, using legitimate Python libraries like “requests” and “pywin32.” These libraries help the malware blend into normal system activities, making it harder to identify. Additionally, much of the malicious code exists only in memory, which makes detection even more challenging.
This fileless technique helps the malware evade traditional security solutions that rely on file-based scanning.
To mitigate this threat, experts recommend organizations adopt several key strategies. Implementing application whitelisting, keeping systems updated with the latest patches, and monitoring for suspicious DLL loading patterns are essential. Configuring Windows to prioritize system directories when searching for DLLs can also reduce the risk of DLL side-loading attacks. These measures help prevent attackers from exploiting vulnerabilities and gaining unauthorized access to sensitive systems, especially in sectors like healthcare and finance.
