Security researchers have uncovered a novel variant of a dynamic link library (DLL) search order hijacking technique that poses a potential threat to systems running Microsoft Windows 10 and Windows 11. The technique, detailed by cybersecurity firm Security Joes, leverages executables in the trusted WinSxS folder, enabling threat actors to execute malicious code without the need for elevated privileges. Unlike traditional DLL search order hijacking methods, this approach introduces a subtle and stealthy exploitation method, emphasizing the importance of monitoring activities within the WinSxS folder. Security Joes warns that this technique could introduce potentially vulnerable binaries into the attack chain, necessitating organizations to take precautions to mitigate its exploitation within their environments.
DLL search order hijacking involves manipulating the search order used to load DLLs, allowing threat actors to execute malicious payloads for defense evasion, persistence, and privilege escalation. The new variant targets files in the trusted “C:\Windows\WinSxS” folder, a critical Windows component used for OS customization and updating. Security Joes’ co-founder and CEO, Ido Naor, describes the discovery as a departure from traditional techniques, introducing a more subtle and stealthy method of exploitation. The technique involves finding vulnerable binaries in the WinSxS folder and strategically placing a custom DLL with the same name as a legitimate one into an actor-controlled directory to achieve code execution.
Executing a vulnerable file in the WinSxS folder, combined with setting the custom folder containing the rogue DLL as the current directory, triggers the execution of the DLL’s contents without copying the executable from the WinSxS folder. Security Joes recommends organizations examine parent-child relationships between processes, especially focusing on trusted binaries, and closely monitor activities performed by binaries residing in the WinSxS folder, emphasizing both network communications and file operations. The discovery underscores the need for heightened cybersecurity measures to detect and mitigate this sophisticated DLL search order hijacking variant effectively.
