youssefnoob003-SindriKit/docs/domains/injection/techniques.md

Injection Techniques

Injection operations follow the same Dependency Injection and state machine patterns used throughout SindriKit. Every technique advances a shared snd_inj_ctx_t through discrete stages and delegates all cross-process work to ctx->proc_api.

Prerequisite reading: Process primitives, Dependency Injection

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Architecture: One Context, Many Techniques

flowchart TB
    subgraph shared ["Shared (all techniques)"]
        CTX["snd_inj_ctx_t"]
        PROC["proc_api → snd_process_api_t"]
    end

    subgraph classic ["Classic technique (implemented)"]
        ENG["snd_inj_classic_* engine"]
        SH["snd_inj_classic_shell"]
        PE["snd_inj_classic_pe"]
    end

    subgraph future ["Future techniques"]
        APC["APC queue …"]
        HIJ["Thread hijack …"]
    end

    CTX --> ENG
    ENG --> SH
    ENG --> PE
    CTX -.-> APC
    CTX -.-> HIJ
    PROC --> ENG

Future techniques will add their own engine headers (e.g. injection/apc/engine.h) but continue to mutate the same snd_inj_ctx_t. Technique-specific metadata, if ever needed, lives in technique-local structures passed alongside the shared context — not in a forked injection context type.

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Shared Stage Machine (snd_inj_stage_t)

Stage	Set by	Meaning
SND_INJ_STAGE_UNINITIALIZED	—	Context created, not started
SND_INJ_STAGE_TARGET_ACQUIRED	snd_inj_classic_open_target	Handle to target process
SND_INJ_STAGE_MEMORY_ALLOCATED	snd_inj_classic_alloc_remote	RW region reserved in remote process
SND_INJ_STAGE_PAYLOAD_WRITTEN	snd_inj_classic_write_payload	Payload bytes copied remotely
SND_INJ_STAGE_PROTECTIONS_SET	snd_inj_classic_set_protections	Remote region transitioned to RX
SND_INJ_STAGE_EXECUTED	snd_inj_classic_execute	Remote thread created

Each engine function validates the current stage and returns SND_STATUS_INVALID_STAGE_SEQUENCE on mismatch. This ordering is enforced for all classic paths and will be reused by future techniques that build on the same remote write/execute primitives.

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Classic Technique: Shellcode (snd_inj_classic_shell)

The baseline Alloc → Write → Protect → Execute pattern. The payload buffer is treated as opaque shellcode — the thread starts at remote_base (allocation base), not at an PE entry point.

Pipeline

1. Open target — proc_api->open_process(target_pid, PROCESS_ALL_ACCESS, …)
2. Allocate remote — payload->size bytes, MEM_COMMIT | MEM_RESERVE, PAGE_READWRITE
3. Write payload — proc_api->write_remote copies the full shellcode buffer
4. Protect — single proc_api->protect_remote call: PAGE_READWRITE → PAGE_EXECUTE_READ over the entire allocation
5. Execute — proc_api->create_remote_thread at remote_entry_point (or remote_base if NULL), parameter NULL

OpSec notes

• Avoids allocating PAGE_EXECUTE_READWRITE directly (RW then RX is a common evasion pattern).
• The shellcode path does not parse PE structures or touch the loader domain.
• Backend choice (snd_proc_win / _nt / _sys) determines telemetry surface — see process primitives.

Example (pocs/inject_shell/main.c)

snd_inj_ctx_t inj_ctx = {0};
inj_ctx.target_pid = target_pid;
inj_ctx.payload    = &shellcode_buf;
inj_ctx.proc_api   = &snd_proc_win;  // or snd_proc_sys after syscall bootstrap

snd_status_t status = snd_inj_classic_shell(&inj_ctx);
snd_inj_cleanup(&inj_ctx);

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Classic Technique: PE (snd_inj_classic_pe)

High-level orchestrator linking a reflective loader context (snd_ldr_pe_ctx_t) with the shared injection context (snd_inj_ctx_t). The PE is parsed, mapped, relocated, and import-fixed locally, then the fixed image bytes are written into the remote process. Execution starts at the remote entry point (remote_base + AddressOfEntryPoint).

This is not a full in-remote reflective load — fixups happen in local memory using the loader engine, then the baked image is marshaled cross-process.

Interleaved pipeline

The PE chain deliberately interleaves loader and injection stages so relocations use the remote base as the execution address:

Step	Component	Action
1	Loader	snd_pe_parse(ldr_ctx->raw_source, FALSE, &ldr_ctx->pe) → SND_STAGE_PARSED
2	Loader	snd_ldr_pe_compatibility_check
3	Loader	snd_ldr_pe_allocate_and_copy_image — local RW mapping
4	Injection	inj_ctx->payload <- local mapped buffer (local_base, allocated_size)
5	Injection	snd_inj_classic_open_target
6	Injection	snd_inj_classic_alloc_remote — remote RW region sized to allocated_size
7	Loader	ldr_ctx->target.execution_base = inj_ctx->remote_base
8	Loader	snd_ldr_pe_apply_relocations — delta = remote_base − ImageBase
9	Loader	snd_ldr_pe_resolve_imports — IAT patched locally
10	Injection	snd_inj_classic_write_payload — writes baked image to remote
11	Injection	snd_inj_classic_set_protections — flat PAGE_EXECUTE_READ on remote region
12	Injection	remote_entry_point = remote_base + ep_rva; snd_inj_classic_execute

Key behaviors:

• execution_base on the loader context is set to the remote allocation address before relocations so the delta matches where the image will run.
• Per-section protections (snd_ldr_pe_apply_memory_protections) are not called — the injection path applies a single RX protection over the entire remote allocation.
• TLS callbacks are not invoked in the current PE injection chain.
• Local execution (snd_ldr_pe_execute_image) is blocked when local_base != execution_base; detach/free similarly refuse remote-prepared images.

For DLL payloads, the remote thread starts at AddressOfEntryPoint (the DLL entry symbol, typically DllMain) with NULL thread parameter — not a typed DllMain(hinst, DLL_PROCESS_ATTACH, NULL) call. Do not assume DLL_PROCESS_ATTACH semantics; this differs from local snd_ldr_pe_execute_image in chain.c.

Example (pocs/inject_pe/main.c)

snd_ldr_pe_ctx_t ldr_ctx = {0};
snd_inj_ctx_t    inj_ctx = {0};

ldr_ctx.mem_api    = &snd_mem_sys;
ldr_ctx.mod_api    = &snd_mod_nt;
ldr_ctx.raw_source = &file_buf;

inj_ctx.target_pid = target_pid;
inj_ctx.proc_api   = &snd_proc_sys;

snd_status_t status = snd_inj_classic_pe(&ldr_ctx, &inj_ctx);
snd_inj_cleanup(&inj_ctx);

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Cleanup

snd_inj_cleanup closes remote_thread and target_process via proc_api->close_handle, clears remote fields, and resets stage to UNINITIALIZED. It does not free the local loader mapping — callers manage snd_ldr_pe_free_mapped_image separately if a local snd_ldr_pe_ctx_t was used.

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Planned Techniques

Future injection techniques will reuse snd_inj_ctx_t and proc_api:

Technique	Description
APC queue	Queue user APC to an alertable thread via NtQueueApcThread
Thread hijack	Suspend thread, rewrite context, resume
Process hollowing	Replace remote image in situ (loader + injection coordination)

Each will add technique-specific engine headers under include/sindri/injection/<technique>/ without forking the shared context type.