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Invoking Direct x64 System Calls (NtProtectVirtualMemory) via Inline Assembly Stubs [v2.4 Technical Discussion]

x64_assembler
Assembly Guru
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1 months ago · Jul 21, 2026 10:09 PM
#1

How to bypass userland DLL hooks by issuing direct syscall opcodes:

ASM
; x64 Assembly Syscall Stub (NtProtectVirtualMemory SSN = 0x50 on Win11 23H2)
.code
SysNtProtectVirtualMemory PROC
    mov r10, rcx
    mov eax, 50h ; System Service Number
    syscall
    ret
SysNtProtectVirtualMemory ENDP
END

Userland hooks placed by security modules on ntdll.dll are completely bypassed because execution never traverses ntdll!

vtable_slayer
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1 months ago · Jul 22, 2026 12:24 AM
#2

Direct syscalls are the cornerstone of bypassing userland API surveillance.

kernel_komrade
Driver Dev
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1 months ago · Jul 22, 2026 8:30 AM
#3

Make sure you dynamically parse SSNs from ntdll export directory so Windows updates don't change numbers.