|Compile After Delivery
|Indicator Removal from Tools
|Dynamic API Resolution
|LNK Icon Smuggling
Adversaries may smuggle commands to download malicious payloads past content filters by hiding them within otherwise seemingly benign windows shortcut files. Windows shortcut files (.LNK) include many metadata fields, including an icon location field (also known as the
IconEnvironmentDataBlock) designed to specify the path to an icon file that is to be displayed for the LNK file within a host directory.
Adversaries may abuse this LNK metadata to download malicious payloads. For example, adversaries have been observed using LNK files as phishing payloads to deliver malware. Once invoked (e.g., Malicious File), payloads referenced via external URLs within the LNK icon location field may be downloaded. These files may also then be invoked by Command and Scripting Interpreter/System Binary Proxy Execution arguments within the target path field of the LNK.
LNK Icon Smuggling may also be utilized post compromise, such as malicious scripts executing an LNK on an infected host to download additional malicious payloads.
Use signatures or heuristics to detect malicious LNK and subsequently downloaded files.
|Behavior Prevention on Endpoint
On Windows 10, enable Attack Surface Reduction (ASR) rules to prevent execution of potentially obfuscated scripts or payloads.
Monitor for downloaded malicious files, though developing rules for the different variants, with a combination of different encoding and/or encryption schemes, may be very challenging. Consider monitoring files downloaded from the Internet, possibly by LNK Icon Smuggling, for suspicious activities. Data and events should not be viewed in isolation, but as part of a chain of behavior that could lead to other activities.
Monitor contextual data about a file that may highlight embedded malicious content, which may include information such as name, the content (ex: signature, headers, or data/media), file size, etc.; correlate with other suspicious behavior to reduce false positives.