DLL

What the technique is

Adversaries may abuse dynamic-link library files (DLLs) in order to achieve persistence, escalate privileges, and evade defenses. DLLs are libraries that contain code and data that can be simultaneously utilized by multiple programs. While DLLs are not malicious by nature, they can be abused through mechanisms such as side-loading, hijacking search order, and phantom DLL hijacking. Specific ways DLLs are abused by adversaries include: DLL Sideloading Adversaries may execute their own malicious payloads by side-loading DLLs. Side-loading involves hijacking which DLL a program loads by planting and then invoking a legitimate application that executes their payload(s). Side-loading positions both the victim application and malicious payload(s) alongside each other. Adversaries likely use side-loading as a means of masking actions they perform under a legitimate, trusted, and potentially elevated system or software process. Benign executables used to side-load payloads may not be flagged during delivery and/or execution. Adversary payloads may also be encrypted/packed or otherwise obfuscated until loaded into the memory of the trusted process. Adversaries may also side-load other packages, such as BPLs (Borland Package Library). Adversaries may chain DLL sideloading multiple times to fragment functionality hindering analysis. […]

What MITRE says you would watch

• AN0577

  DLL hijacking behaviors including unexpected DLL loads from non-standard directories, replacement of DLLs, phantom DLL insertion, redirection file creation, and substitution of legitimate DLLs. Defender correlates file system modifications, registry changes, and module load telemetry to detect abnormal DLL behavior in trusted processes.