Dynamic-link library (DLL) side-loading occurs when Windows Side-by-Side (WinSxS) manifests are not explicit about the characteristics of DLLs being loaded by a program. In layman’s terms, DLL side-loading can allow an attacker to trick a program into loading a malicious DLL. If you are interested in learning more about how DLL side-loading works and how we see attackers using this technique, read through our whitepaper.
DLL hijacking occurs when an attacker is able to take advantage of the Windows search and load order, allowing the execution of a malicious DLL, rather than the legitimate DLL.
DLL side-loading and hijacking has been around for years; in fact, FireEye Mandiant was one of the first to discover the DLL side-loading technique along with DLL search order hijacking back in 2010. So why are we still writing a blog about it? Because it’s still a method that works and is used in real world intrusions! FireEye Mandiant still identifies and observes threat groups using DLL abuse techniques during incident response (IR) engagements. There are still plenty of signed executables vulnerable to this, and our red team has weaponized DLL abuse techniques to be part of our methodology.