Code d'attaque

name: offensive-shellcode

description: "Shellcode development reference for offensive security engagements. Use when writing custom x86/x64 shellcode, implementing position-independent code (PIC), building shellcode loaders, evading AV/EDR detection, or converting PE files to shellcode. Covers null byte avoidance, API hashing, encoder/decoder patterns, staged vs stageless payloads, Windows PEB traversal, and cross-platform shellcode techniques."

Shellcode Development Workflow

1. Define concept and target platform (x86/x64, Windows/Linux/macOS)
2. Write assembly using position-independent techniques
3. Extract binary and test in controlled environment
4. Apply null byte avoidance and optimizations
5. Encode/encrypt to evade static detection
6. Package with loader and choose delivery method

Basic Concepts

Execution Pattern (Allocate-Write-Execute)

Avoid direct PAGE_EXECUTE_READWRITE — prefer:

1. Allocate with PAGE_READWRITE
2. Write shellcode to allocated region
3. Call VirtualProtect to switch to PAGE_EXECUTE_READ

char *dest = VirtualAlloc(NULL, 0x1234, MEM_COMMIT|MEM_RESERVE, PAGE_READWRITE);
memcpy(dest, shellcode, 0x1234);
VirtualProtect(dest, 0x1234, PAGE_EXECUTE_READ, &old);
((void(*)())dest)();

Position-Independent Code (PIC) Techniques

Windows API Resolution (PEB Walk)

Identifying kernel32.dll without imports:

1. Get PEB via gs:[0x60] (x64) or fs:[0x30] (x86)
2. Walk PEB->Ldr.InMemoryOrderModuleList — order: exe → ntdll → kernel32
3. Hash-compare module names to locate kernel32
4. Parse the Export Address Table (EAT)
5. Find GetProcAddress by name hash, then resolve LoadLibraryA
6. Use LoadLibraryA to load WS2_32.dll, resolve Winsock functions

WinDbg helpers for debugging PEB walk:

dt nt!_TEB -y ProcessEnvironmentBlock @$teb
dt nt!_PEB -y Ldr <peb_addr>
dt -r _PEB_LDR_DATA <ldr_addr>
dt _LDR_DATA_TABLE_ENTRY (<init_flink_addr> - 0x10)
lm m kernel32   # verify base address
r @r8           # check register

Shellcode Loaders

Loader Responsibilities

• Environment verification / keying (sandbox detection)
• Shellcode decryption
• Safe memory allocation and injection
• Ends its duties after injecting

Recommended languages: Zig (small, no runtime), Rust (secure), Nim, Go (watch for runtime signatures)

Allocation Phase

Avoid RWX allocations — use two-step:

• VirtualAllocEx / NtAllocateVirtualMemory — allocate RW
• ZwCreateSection + NtMapViewOfSection — alternative approach
• After writing: VirtualProtectEx to switch to RX

Other options: code caves, stack/heap (with DEP disabled)

Write Phase

• WriteProcessMemory / NtWriteVirtualMemory
• memcpy to mapped section

Evasion tips:

• Prepend shellcode with dummy opcodes
• Split into chunks, write in randomized order
• Add delays between writes

Execute Phase

Most scrutinized step — EDR checks thread start address against image-backed memory:

Indirect execution resources:

• FlavorTown
• AlternativeShellcodeExec
• ThreadlessInject

PE-to-Shellcode Conversion

Open-source loaders:

• ScareCrow
• NimPackt-v1
• NullGate — indirect syscalls + junk-write sequencing
• DripLoader — chunked RW writes + direct syscalls + JMP trampoline
• ProtectMyTooling — chain multiple protections
• Direct-syscall helpers: SysWhispers3, FreshyCalls (now baseline requirements)

Shellcode Storage & Hiding