Binary Protection Bypass

SKILL: Binary Protection Bypass — Expert Attack Playbook

> AI LOAD INSTRUCTION: Expert binary protection identification and bypass techniques. Covers ASLR, PIE, NX, RELRO, canary, FORTIFY_SOURCE, stack clash, CET shadow stack, and ARM MTE. Each protection is paired with its bypass methods and required primitives. Distilled from ctf-wiki mitigation sections and real-world exploitation. Base models often confuse which protections block which attacks and miss the combinatorial effect of multiple protections.

0. RELATED ROUTING

• [stack-overflow-and-rop](../stack-overflow-and-rop/SKILL.md) — ROP chains to bypass NX, ret2libc for ASLR bypass
• [format-string-exploitation](../format-string-exploitation/SKILL.md) — primary method for leaking canary, PIE, libc addresses
• [heap-exploitation](../heap-exploitation/SKILL.md) — heap attacks for RELRO bypass (when GOT is read-only)
• [arbitrary-write-to-rce](../arbitrary-write-to-rce/SKILL.md) — what to overwrite when GOT is protected by RELRO

Advanced Reference

Load [PROTECTIONBYPASSMATRIX.md](./PROTECTIONBYPASSMATRIX.md) for comprehensive protection × bypass × primitive matrix.

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1. PROTECTION IDENTIFICATION

$ checksec ./binary
[*] '/path/to/binary'
    Arch:     amd64-64-little
    RELRO:    Full RELRO          ← GOT read-only
    Stack:    Canary found        ← stack canary enabled
    NX:       NX enabled          ← stack not executable
    PIE:      PIE enabled         ← position-independent code
    FORTIFY:  Enabled             ← fortified libc functions

Quick Identification Table

| Protection | Check Command | Binary Indicator | |---|---|---| | ASLR | cat /proc/sys/kernel/randomize_va_space | OS-level (0=off, 1=partial, 2=full) | | PIE | checksec or readelf -h (Type: DYN) | Binary compiled with -pie | | NX | checksec or readelf -l (no RWE segment) | gcc -z noexecstack (default on) | | Canary | checksec or look for __stack_chk_fail@plt | gcc -fstack-protector-all | | Partial RELRO | readelf -l (GNU_RELRO segment, .got.plt writable) | gcc -Wl,-z,relro | | Full RELRO | readelf -l + .got section read-only | gcc -Wl,-z,relro,-z,now | | FORTIFY | Presence of __printf_chk, __memcpy_chk etc. | gcc -D_FORTIFY_SOURCE=2 |

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2. ASLR BYPASS

ASLR randomizes base addresses of stack, heap, libc, and mmap regions at each execution.

| Bypass Method | Required Primitive | Notes | |---|---|---| | Information leak | Any read primitive (format string, OOB read, UAF) | Leak libc/stack/heap address → calculate base | | Partial overwrite | Write primitive (limited length) | Overwrite last 1-2 bytes (page offset fixed) | | Brute force (32-bit) | Ability to reconnect/retry | ~256–4096 attempts (8-12 bits entropy) | | Return-to-PLT | Stack overflow | PLT addresses are at fixed offset from binary base (if no PIE) | | ret2dlresolve | Stack overflow + write primitive | Resolve arbitrary function without knowing libc base | | Format string leak | Format string vulnerability | %N$p for stack/libc/heap addresses | | Stack reading | Byte-by-byte (fork server) | Read stack byte-by-byte via crash oracle |

ASLR Entropy (x86-64 Linux)

| Region | Entropy (bits) | Positions | |---|---|---| | Stack | 22 | ~4M | | mmap / libc | 28 | ~256M | | Heap (brk) | 13 | ~8K | | PIE binary | 28 | ~256M |

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3. PIE BYPASS

PIE (Position Independent Executable) randomizes the binary's own code/data base address.

| Bypass Method | Required Primitive | Notes | |---|---|---| | Information leak | Read return address from stack | PIE base = leakedaddr - knownoffset | | Partial overwrite | One-byte or two-byte write | Last 12 bits of page offset are fixed | | Format string leak | Format string vulnerability | %N$p where N points to .text return address | | Relative addressing | Knowledge of binary layout | If you know relative offsets, only need one leak |

Partial Overwrite Details

PIE binary loaded at: 0x555555554000 (example)
Function at offset 0x1234: 0x555555555234

Overwrite return address last 2 bytes: 0x?234 → 0x?XXX
Unknown: bits 12-15 (one nibble = 4 bits = 16 possibilities)
Success rate: 1/16 per attempt

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4. NX / DEP BYPASS

NX (No-eXecute) / DEP (Data Execution Prevention) prevents execution of code on the stack/heap.

| Bypass Method | Detail | |---|---| | ROP (Return-Oriented Programming) | Chain existing code gadgets ending in ret | | ret2libc | Call libc functions (system, execve) directly | | ret2csu | Use __libc_csu_init gadgets for controlled function calls | | ret2dlresolve | Forge dynamic linker structures to resolve arbitrary functions | | SROP | Use sigreturn to set all registers from fake signal frame | | mprotect ROP | Chain mprotect(addr, size, PROT_RWX) → make page executable → jump to shellcode | | JIT spray | In JIT environments (V8, etc.), create executable code via JIT compiler |

mprotect Chain

# Make stack executable, then jump to shellcode
rop = b'A' * offset
rop += p64(pop_rdi) + p64(stack_page)     # page-aligned address
rop += p64(pop_rsi) + p64(0x1000)         # size
rop += p64(pop_rdx) + p64(7)              # PROT_READ|PROT_WRITE|PROT_EXEC
rop += p64(mprotect_addr)
rop += p64(shellcode_addr)                 # jump to shellcode on now-executable stack

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5. RELRO BYPASS

| RELRO Level | GOT Status | Bypass | |---|---|---| | No RELRO | GOT fully writable | Direct GOT overwrite | | Partial RELRO | .got.plt writable (lazy binding) | GOT overwrite still works | | Full RELRO | All GOT entries resolved at load, GOT read-only | Cannot write GOT → target other structures |

Full RELRO Alternative Targets

| Target | When | How | |---|---|---| | __malloc_hook | glibc < 2.34 | Overwrite with one_gadget | | __free_hook | glibc < 2.34 | Overwrite with system, trigger free("/bin/sh") | | _IO_FILE vtable | Any glibc | FSOP / vtable hijack | | __exit_funcs | Any glibc | Overwrite exit handler list | | TLS_dtor_list | glibc ≥ 2.34 | Thread-local destructor list (needs pointer guard) | | .fini_array | If writable | Overwrite destructor function pointers | | Stack return address | Direct stack write | Overwrite return address for ROP |

See [arbitrary-write-to-rce](../arbitrary-write-to-rce/SKILL.md) for comprehensive target list.

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6. CANARY BYPASS

| Method | Condition | Detail | |---|---|---| | Format string leak | printf(userinput) | %N$p to read canary from stack | | Brute-force | fork() server (canary persists in child) | Byte-by-byte: 256 × (canarysize-1) attempts | | Stack reading | Partial overwrite / info leak | Overwrite canary's null byte, leak via output | | Thread canary overwrite | Overflow reaches TLS | Canary at fs:[0x28]; overflow past buffer to TLS → overwrite canary with known value | | Canary-relative overwrite | Overflow after canary but before return addr | Skip canary, only overwrite return address (rare layout) | | Heap-based | Vulnerability is on heap, not stack | Canary only protects stack | | __stackchkfail GOT overwrite | Partial RELRO | Overwrite __stack_chk_fail@GOT to point to harmless function → canary check passes |

Canary Format

x86:    0x00XXXXXX (4 bytes, leading null byte)
x86-64: 0x00XXXXXXXXXXXXXX (8 bytes, leading null byte)

The leading \x00 prevents string operations from accidentally reading the canary.

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7. FORTIFY_SOURCE BYPASS

_FORTIFY_SOURCE=2 adds buffer size checking and restricts format string operations.

| Fortified Function | Restriction | Bypass | |---|---|---| | __printf_chk | %n with positional args (%N$n) forbidden | Use non-positional %n or %hn chain | | __memcpy_chk | Destination buffer size checked | Use heap overflow instead of stack | | __strcpy_chk | Same | | | __read_chk | Read size checked against buffer | |

Format String with FORTIFY_SOURCE

# %1$n is blocked by __printf_chk
# But sequential (non-positional) %n may still work:
# Print exact byte count, then %hn — must be very precise
# Or: find unfortified printf in binary/libc via ROP

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8. CET (Control-flow Enforcement Technology)

Intel CET adds two mechanisms:

Shadow Stack

• Hardware-maintained copy of return addresses
• On ret, CPU checks shadow stack matches actual stack
• Mismatch → #CP fault (control protection exception)

| Impact | Detail | |---|---| | ROP blocked | Return address overwrite detected on ret | | JOP possible | jmp [reg] not checked by shadow stack | | COP possible | call [reg] pushes to shadow stack but target validated by IBT |

Indirect Branch Tracking (IBT)

• Indirect jmp/call must land on ENDBR64 instruction
• Non-ENDBR landing → #CP fault

Bypass:

• Data-only attacks (don't change control flow)
• Find valid ENDBR gadgets that chain into useful operations
• JOP with ENDBR-prefixed gadgets
• Target structures outside CFI scope (modprobe_path, function pointer arrays)

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9. MTE (Memory Tagging Extension, ARM)

ARM MTE assigns 4-bit tags to memory pointers and allocations. Tag mismatch = fault.

| Aspect | Detail | |---|---| | Tag bits | 4 bits in pointer (bits 56-59) = 16 possible tags | | Granule | 16 bytes (each 16-byte granule has one tag) | | Check | Load/store: pointer tag must match memory tag | | Probabilistic | Random tag → 1/16 chance attacker guesses correctly |

Bypass Approaches

| Method | Success Rate | |---|---| | Brute-force | 1/16 per attempt (6.25%) | | Tag oracle | Side-channel to determine tag (timing, error messages) | | In-bounds exploit | Stay within same tagged region (use relative offsets) | | Tag bypass gadget | Use LDGM/STGM instructions if accessible | | Speculative execution | Spectre-style bypass of tag check |

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10. DECISION TREE

Binary analysis: checksec output
├── NX disabled?
│   └── Shellcode on stack/heap (simplest path)
│
├── NX enabled (standard modern binary)?
│   ├── Need code execution → ROP/ret2libc
│   │
│   ├── Canary enabled?
│   │   ├── fork server? → byte-by-byte brute-force
│   │   ├── Format string? → leak canary via %p
│   │   ├── Heap vuln? → canary doesn't protect heap
│   │   └── Partial RELRO? → overwrite __stack_chk_fail@GOT
│   │
│   ├── PIE enabled?
│   │   ├── Format string? → leak .text address → PIE base
│   │   ├── Partial overwrite → last 12 bits fixed (1/16 brute-force)
│   │   └── OOB read? → leak code pointer
│   │
│   ├── ASLR enabled?
│   │   ├── Info leak available → leak libc base
│   │   ├── No leak → ret2dlresolve or SROP
│   │   ├── 32-bit? → brute-force feasible (~4096 attempts)
│   │   └── Return-to-PLT (no libc base needed for PLT calls)
│   │
│   ├── RELRO level?
│   │   ├── None/Partial → GOT overwrite
│   │   └── Full → alternative targets:
│   │       ├── glibc < 2.34 → __malloc_hook / __free_hook
│   │       ├── glibc ≥ 2.34 → _IO_FILE / exit_funcs / TLS_dtor_list
│   │       ├── .fini_array (if writable)
│   │       └── Stack return address
│   │
│   └── FORTIFY_SOURCE?
│       ├── Blocks positional %n → use sequential %n or heap exploit
│       └── Blocks buffer overflows in fortified functions → use unfortified paths
│
├── CET (shadow stack)?
│   ├── ROP blocked → data-only attack or JOP
│   └── ENDBR-gadget chaining
│
└── MTE (ARM)?
    ├── 1/16 brute-force
    └── Stay in-bounds for relative corruption

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: yaklang
• Source: yaklang/hack-skills
• License: MIT

Install and usage instructions live in the source repository linked above.