NEEDS TESTING: Syscall Signature (fresh ntdll load)

[kevross33]

So this needs testing please as I don't have a current CAPE until i am back in office/have new home lab PC in a few weeks.

The logic of this is that the Windows loader should take care of NTDLL. Loading a fresh NTDLL into itself from disk likely is then to begin parsing it for syscall instruction for doing that or to bypass hooking.

Here are two samples that do this for testing each element:

1. AgentTesla https://capesandbox.com/analysis/46120/

This uses NTCreateFile on ntdll to load it and then NtReadFile to read it into memory.

2. LUMMA https://capesandbox.com/analysis/46359/

This uses NTCreateFile on ntdll to load it then maps in into its memory with NTCreateSection before changing the memory protections on it (likely to then patch it and remove hooks).

There is another possible indirect syscall detection where ntdll is in memory where it starts parsing that for the sycall bytes. If I can find a sample doing that I will try and work out how to sig it if possible.

[gemini-code-assist]

Summary of Changes

Hello @kevross33, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new Cuckoo signature designed to detect sophisticated malware techniques that involve loading a fresh copy of ntdll.dll from disk. This behavior is often a precursor to syscall unhooking or anti-EDR bypass, where malware attempts to remove security product hooks by replacing the in-memory ntdll.dll with an untampered version. The signature aims to enhance detection capabilities against such evasion tactics by monitoring specific file and memory manipulation API calls related to ntdll.dll.

Highlights

• New Signature Added: Introduced a new Cuckoo signature named Suspicious_NTDLL_DiskLoad to detect advanced anti-EDR and syscall unhooking techniques.
• Detection Logic: The signature identifies suspicious activity where ntdll.dll is loaded from disk, mapped into memory, and its memory protections are altered (e.g., to PAGE_EXECUTE_READWRITE).
• Monitored APIs: It monitors key Windows API calls including NtCreateFile, NtCreateSection, NtOpenFile, NtProtectVirtualMemory, and NtReadFile to track the lifecycle of ntdll.dll manipulation.
• MITRE ATT&CK Mapping: The signature is mapped to MITRE ATT&CK TTP T1106 (Native API) for better threat intelligence correlation.

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[gemini-code-assist]

Code Review

This pull request introduces a new Cuckoo signature to detect malware that loads a fresh copy of ntdll.dll from disk to bypass EDR hooks. The logic correctly identifies two common patterns involving NtReadFile and NtCreateSection/NtProtectVirtualMemory. However, the implementation contains several critical bugs, including syntax errors, incorrect use of operators, and unsafe handling of API arguments, which would prevent the signature from working correctly. I've provided detailed comments and suggestions to fix these issues.