NtInitializeEnclave

Prototype

NTSTATUS NtInitializeEnclave(
  HANDLE  ProcessHandle,
  PVOID   BaseAddress,
  PVOID   EnclaveInformation,
  ULONG   EnclaveInformationLength,
  PULONG  EnclaveError
);

Arguments

Syscall IDs by Windows version

Syscall stub

4C 8B D1            mov r10, rcx
B8 07 01 00 00      mov eax, 0x107
F6 04 25 08 03 FE 7F 01   test byte ptr [0x7FFE0308], 1
75 03               jne short +3
0F 05               syscall
C3                  ret
CD 2E               int 2Eh
C3                  ret

Undocumented notes

`NtInitializeEnclave` is the **measurement-and-seal** step. By the time it is called, the host has used `NtLoadEnclaveData` to copy the enclave image (and its data pages) into the reserved VTL1 range. Initialisation does three things: (1) compute the enclave's identity hash (MRENCLAVE on SGX, image-hash on VBS), (2) verify the developer signature against the embedded `IMAGE_ENCLAVE_CONFIG` policy and — on VBS — against HVCI's allowed-enclave list, (3) flip the enclave from a *loading* state to an *executable* state. After this call, no further `NtLoadEnclaveData` is permitted on the enclave: its memory layout is frozen. The `ThreadCount` field of `ENCLAVE_INIT_INFO_VBS` reserves the maximum number of enclave threads (analogous to SGX TCS count) — this is the count of host threads that can simultaneously be inside the enclave via `NtCallEnclave`.

Common malware usage

An adversary who has reached `NtInitializeEnclave` has already passed image signing — the practical attacks happen *before* this call (planting a benign-looking enclave image), or rely on a bug *inside* a Microsoft-signed enclave that exposes a primitive callable post-init (the Recon 2023 work). The init call itself is just the trip wire that grants execution. Defenders should care that a successful return means a verified-signed enclave is now live; an attacker holding a stolen Microsoft enclave key would chain `NtCreateEnclave` → `NtLoadEnclaveData` (× N) → `NtInitializeEnclave` → `NtCallEnclave` to bootstrap an unauditable VTL1 payload. No commodity malware is publicly known to do this end-to-end today.

Detection opportunities

ETW `Microsoft-Windows-Kernel-Memory` event 6 (VBS enclave activity) and the `Microsoft-Windows-Hyper-V-Worker/Operational` log both record a successful initialisation. Cross-reference with the `Microsoft-Windows-Security-Mitigations` log to confirm the enclave's image hash. Any init coming from a process whose loaded modules do *not* contain a Microsoft-rooted `IMAGE_ENCLAVE_CONFIG.EnclaveFlags = ENCLAVE_FLAG_PRIMARY_IMAGE` and an MS-issued signer is high signal — almost certainly a research tool, a Microsoft Insider build component, or an attacker with a stolen key. Pair the syscall with the host's full process tree for context: legitimate enclave hosts (LsaIso, vmms, vmcompute) have a stable launch ancestry.

Direct syscall examples

// After CreateEnclave + LoadEnclaveData (the enclave DLL is now mapped into VTL1),
// initialise to lock layout and verify the signature against HVCI's allowlist.
#include <windows.h>

typedef struct _ENCLAVE_INIT_INFO_VBS {
    ULONG Length;
    ULONG ThreadCount;
} ENCLAVE_INIT_INFO_VBS;

BOOL FinalizeVbsEnclave(PVOID enclaveBase) {
    ENCLAVE_INIT_INFO_VBS init = {0};
    init.Length = sizeof(init);
    init.ThreadCount = 4;             // max concurrent host->enclave calls
    DWORD enclaveError = 0;
    if (!InitializeEnclave(
            GetCurrentProcess(),
            enclaveBase,
            &init, sizeof(init),
            &enclaveError)) {
        // STATUS_ENCLAVE_NOT_TERMINATED / STATUS_INVALID_SIGNATURE / etc.
        return FALSE;
    }
    return TRUE;
}

; Direct syscall stub for NtInitializeEnclave (SSN 0x107 on Win11 24H2 / Server 2025)
NtInitializeEnclave PROC
    mov  r10, rcx          ; ProcessHandle
    mov  eax, 107h         ; SSN
    syscall
    ret
NtInitializeEnclave ENDP

MITRE ATT&CK mappings

• T1620Reflective Code Loadingmitre ↗
• T1574Hijack Execution Flowmitre ↗
• T1106Native APImitre ↗