Create new unbacked execution sig file

[kevross33]

Mostly moved and split out from unbacked_misc/activities (see this for more info). Just as was growing too big.

[gemini-code-assist]

Summary of Changes

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This pull request significantly enhances the detection capabilities for advanced evasion and fileless execution techniques by introducing a dedicated set of signatures. These new signatures focus on identifying various forms of malicious activity originating from dynamically allocated, unbacked memory regions, such as library loading, exception handler registration, process creation, APC queuing, and thread execution. This refactoring centralizes related detection logic, improving maintainability and clarity.

Highlights

• New Unbacked Execution Signatures: Introduced a new signature file unbacked_execution.py containing five distinct signatures to detect various forms of execution originating from dynamically allocated (unbacked) memory.
• Unbacked Library Load Detection: Added UnbackedLibraryLoad signature to identify suspicious DLL loads where the caller address is within unbacked memory regions.
• Unbacked VEH Registration Detection: Implemented UnbackedVehRegistration signature to flag Vectored Exception Handlers (VEH) that point to unbacked memory, often indicative of stealthy techniques.
• Unbacked Process Creation Detection: Included UnbackedProcessCreation signature to detect attempts to spawn child processes from code residing in unbacked memory.
• Unbacked APC Execution Detection: Developed UnbackedMemoryApcExecution signature to identify Asynchronous Procedure Calls (APCs) queued to routines located in unbacked memory.
• Unbacked Thread Creation Detection: Created ThreadUnbackedMemory signature to detect the creation of threads that execute from dynamically allocated, unbacked memory, specifically tracking RWX or RX regions.

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[gemini-code-assist]

Code Review

The pull request introduces a new file with five Cuckoo signatures to detect malicious activities related to unbacked memory. The general idea is sound, but the implementation suffers from significant code duplication across all five signature classes, which makes the code difficult to maintain. Additionally, there is a critical syntax error in one of the classes that will prevent it from running. I've provided suggestions to refactor the duplicated code and fix the syntax error.