ctf-pwn

CTF Binary Exploitation (Pwn)

Quick reference for binary exploitation (pwn) CTF challenges. Each technique has a one-liner here; see supporting files for full details.

Prerequisites

Python packages (all platforms):

pip install "pwntools==4.15.0" "ROPgadget==7.7" "ropper==1.13.13"
# or via script: bash scripts/install_ctf_tools.sh python

uv alternative:

uv venv && uv pip install "pwntools==4.15.0" "ROPgadget==7.7" "ropper==1.13.13"

Linux (apt):

apt install gdb binutils strace ltrace qemu-system-x86

Optional cross-arch (ARM/MIPS — Debian/Ubuntu):

apt install qemu-user qemu-user-static gdb-multiarch binutils-multiarch libc6-armhf-cross libc6-arm64-cross libc6-mips-cross

macOS (Homebrew):

brew install gdb binutils qemu

Ruby gems (all platforms):

gem install one_gadget seccomp-tools

Manual install:

• pwndbg — Linux: GitHub, macOS: brew install pwndbg/tap/pwndbg-gdb
• checksec — included with pwntools (checksec --file=binary)

Additional Resources

• [overflow-basics.md](overflow-basics.md) - Stack/global buffer overflow, ret2win, canary bypass, canary byte-by-byte brute force on forking servers, struct pointer overwrite, signed integer bypass, hidden gadgets, stride-based OOB read leak, parser stack overflow via unchecked memcpy length with callee-saved register restoration
• [rop-and-shellcode.md](rop-and-shellcode.md) - Core ROP chains (ret2libc, syscall ROP, rdx control, shell interaction), ret2csu, bad character XOR bypass, exotic x86 gadgets (BEXTR/XLAT/STOSB/PEXT), stack pivot via xchg rax,esp, sprintf() gadget chaining for bad character bypass, canary XOR epilogue as RDX zeroing gadget, stub_execveat syscall as execve alternative via read() return value
• [rop-advanced.md](rop-advanced.md) - Advanced ROP techniques: double stack pivot to BSS via leave;ret, SROP (Sigreturn-Oriented Programming) with UTF-8 constraints, seccomp bypass, RETF architecture switch (x64→x32) for seccomp bypass, shellcode with input reversal, .fini_array hijack, ret2vdso, pwntools template, x32 ABI syscall aliasing for seccomp bypass, time-based blind shellcode exfiltration
• [format-string.md](format-string.md) - Format string exploitation (leaks, GOT overwrite, blind pwn, filter bypass, canary leak, __free_hook, .rela.plt patching, saved EBP overwrite for .bss pivot, argv[0] overwrite for stack smash info leak, .fini_array loop for multi-stage exploitation, __printf_chk bypass with sequential %p, single-call leak + GOT overwrite, ROT13-encoded format string exploit through input transformation)
• [advanced.md](advanced.md) - Seccomp advanced techniques, UAF, JIT, esoteric GOT, heap overlap via base conversion, tree data structure stack underallocation, ret2dlresolve, kernel exploitation (basic)
• [heap-techniques.md](heap-techniques.md) - House of Apple 2 (+ setcontext SUID variant), House of Einherjar, House of Orange/Spirit/Lore/Force, heap grooming, custom allocators (nginx, talloc), classic unlink, musl libc heap (meta pointer + atexit hijack), tcache stashing unlink attack, unsafe unlink + top chunk consolidation
• [heap-techniques-2.md](heap-techniques-2.md) - CTF-writeup heap variants: UAF vtable pointer encoding shell argument, uninitialized chunk residue pointer leak, tcache strcpy null-byte overflow + backward consolidation, adjacent-struct fn-pointer overflow for libc leak + GOT overwrite, hidden-menu tcache poisoning, tcache double-free + fake _IO_FILE vtable stdout hijack, tcache-to-fastbin promotion cross-bin attack, 6-bit index OOB + written_bytes accumulator, IS_MMAPED bit-flip for unsorted bin leak on calloc'd chunk, filename-regex-constrained fastbin via LSB-only heap pointer overwrite, custom allocator unsafe unlink to GOT
• [heap-fsop.md](heap-fsop.md) - FILE-structure (_IO_FILE) exploitation: fastbin stdout vtable two-stage hijack for PIE + Full RELRO, _IO_buf_base null-byte stdin hijack, glibc 2.24+ _IO_FILE vtable validation bypass, unsorted-bin attack on stdin _IO_buf_end, unsorted-bin corruption via mp_ structure, realloc(ptr, 0) as free() UAF, single-byte reference counter wraparound UAF
• [advanced-exploits.md](advanced-exploits.md) - Advanced exploit techniques (part 1): VM signed comparison, BF JIT shellcode, type confusion, off-by-one index corruption, DNS overflow, ASAN shadow memory, format string with encoding constraints, custom canary preservation, signed integer bypass, canary-aware partial overflow, CSV injection, MD5 preimage gadgets, VM GC UAF slab reuse, path traversal sanitizer bypass, FSOP + seccomp bypass via openat/mmap/write
• [advanced-exploits-2.md](advanced-exploits-2.md) - Advanced exploit techniques (part 2): bytecode validator bypass via self-modification, io_uring UAF with SQE injection, integer truncation int32->int16, GC null-reference cascading corruption, leakless libc via multi-fgets stdout FILE overwrite, signed/unsigned char underflow heap overflow, XOR keystream brute-force write primitive, tcache pointer decryption heap leak, unsorted bin promotion via forged chunk size, FSOP stdout TLS leak, TLS destructor hijack via __call_tls_dtors, custom shadow stack pointer overflow bypass, signed int overflow negative OOB heap write, XSS-to-binary pwn bridge
• [advanced-exploits-4.md](advanced-exploits-4.md) - Advanced exploit techniques (part 4): Windows SEH overwrite + pushad VirtualAlloc ROP, IAT-relative resolution, detached process shell stability, SeDebugPrivilege SYSTEM escalation, ARM buffer overflow with Thumb shellcode, Forth interpreter system word exploitation, GF(2) Gaussian elimination for multi-pass tcache poisoning, single-bit-flip exploitation primitive (mprotect + iterative code patching), Game of Life shellcode evolution via still-lifes, UAF via menu-driven strdup/free ordering, Windows CFG bypass via system() as valid call target, neural network output as function pointer index OOB, shellcode unique-byte limit bypass via counter overflow
• [advanced-exploits-3.md](advanced-exploits-3.md) - Advanced exploit techniques (part 3): stack variable overlap / carry corruption OOB, 1-byte overflow via 8-bit loop counter, game AI arithmetic mean OOB read, arbitrary read/write GOT overwrite to shell, stack leak via __environ + memcpy overflow, JIT sandbox escape via uint16 jump truncation, DNS compression pointer stack overflow with multi-question ROP, ELF code signing bypass via program header manipulation, game level format signed/unsigned coordinate mismatch, file descriptor inheritance via missing O_CLOEXEC, sign extension integer underflow in metadata parsing, ROP chain construction with read-only primitive, 4-byte shellcode with timing side-channel via persistent registers, CRC oracle as arbitrary read, UTF-8 case conversion buffer overflow
• [advanced-exploits-5.md](advanced-exploits-5.md) - Advanced exploit techniques (part 5): data-interpretation exploitation — Chip-8 emulator OOB memory for ret2libc, double-precision float quicksort canary repositioning, bloom filter abs(INT_MIN) negative index OOB write
• [sandbox-escape.md](sandbox-escape.md) - Custom VM exploitation, FUSE/CUSE devices, busybox/restricted shell, shell tricks, process_vm_readv sandbox bypass, named pipe file size bypass, CPU emulator print opcode Python eval injection (cross-references ctf-misc/pyjails.md for Python jail techniques)
• [kernel.md](kernel.md) - Linux kernel exploitation fundamentals: environment setup, QEMU debug, heap spray structures (tty_struct, poll_list, user_key_payload, seq_operations), kernel stack overflow, canary leak, privilege escalation (ret2usr, kernel ROP), modprobe_path overwrite, core_pattern overwrite, kmalloc size mismatch heap overflow + struct file f_op corruption
• [kernel-techniques.md](kernel-techniques.md) - Kernel exploitation techniques: tty_struct kROP (fake vtable + stack pivot), AAW via ioctl register control, userfaultfd race stabilization, SLUB allocator internals (freelist hardening/obfuscation), leak via kernel panic, MADV_DONTNEED race window extension (DiceCTF 2026), cross-cache CPU-split attack (DiceCTF 2026), PTE overlap file write (DiceCTF 2026), addr_limit bypass via failed file open for kernel memory read/write
• [kernel-bypass.md](kernel-bypass.md) - Kernel protection bypass: KASLR/FGKASLR bypass (__ksymtab), KPTI bypass (swapgs trampoline, signal handler, modprobe_path/core_pattern via ROP), SMEP/SMAP bypass, GDB kernel module debugging, initramfs/virtio-9p workflow, exploit templates, exploit delivery
• [field-notes.md](field-notes.md) - Detailed pwn notes: heap exploitation quick reference, additional exploit notes, useful commands

---

When to Pivot

• If you do not yet understand what the binary does, switch to /ctf-reverse before trying to exploit it.
• If the service is really a restricted shell, encoding puzzle, or sandbox language challenge, switch to /ctf-misc.
• If the exploit path depends on a web endpoint, session bug, or upload primitive more than memory corruption, switch to /ctf-web.
• If the vulnerability requires breaking a cryptographic primitive before exploitation, switch to /ctf-crypto.

Quick Start Commands

# Binary analysis
checksec --file=binary
file binary
readelf -h binary

# Find gadgets
ROPgadget --binary binary | grep "pop rdi"
ropper -f binary --search "pop rdi"
one_gadget /lib/x86_64-linux-gnu/libc.so.6

# Debug
gdb -q binary -ex 'start' -ex 'checksec'

# Pattern for offset finding
python3 -c "from pwn import *; print(cyclic(200))"
python3 -c "from pwn import *; print(cyclic_find(0x61616168))"

# libc identification
./libc-database/find puts <leaked_addr_last_3_nibbles>

Source Code Red Flags

• Threading/pthread -> race conditions
• usleep()/sleep() -> timing windows
• Global variables in multiple threads -> TOCTOU

Race Condition Exploitation

bash -c '{ echo "cmd1"; echo "cmd2"; sleep 1; } | nc host port'

Common Vulnerabilities

• Buffer overflow: gets(), scanf("%s"), strcpy()
• Format string: printf(user_input)
• Integer overflow, UAF, race conditions

Protection Implications for Exploit Strategy

| Protection | Status | Implication |

|-----------|--------|-------------|

| PIE | Disabled | All addresses (GOT, PLT, functions) are fixed - direct overwrites work |

| RELRO | Partial | GOT is writable - GOT overwrite attacks possible |

| RELRO | Full | GOT is read-only - need alternative targets (hooks, vtables, return addr) |

| NX | Enabled | Can't execute shellcode on stack/heap - use ROP or ret2win |

| Canary | Present | Stack smash detected - need leak or avoid stack overflow (use heap) |

Quick decision tree:

• Partial RELRO + No PIE -> GOT overwrite (easiest, use fixed addresses)
• Full RELRO -> target __free_hook, __malloc_hook (glibc < 2.34), or return addresses
• Stack canary present -> prefer heap-based attacks or leak canary first

Stack Buffer Overflow

1. Find offset: cyclic 200 then cyclic -l <value>
2. Check protections: checksec --file=binary
3. No PIE + No canary = direct ROP
4. Canary leak via format string or partial overwrite
5. Canary brute-force byte-by-byte on forking servers (7*256 attempts max)

ret2win with magic value: Overflow -> ret (alignment) -> pop rdi; ret -> magic -> win(). Stack alignment: SIGSEGV in movaps = add extra ret gadget. Offset: buffer at rbp - N, return at rbp + 8, total = N + 8. Input filtering: assert payload avoids memmem() banned strings. Gadgets: ROPgadget --binary binary | grep "pop rdi", or pwntools ROP() for hidden gadgets in CMP immediates. See [overflow-basics.md](overflow-basics.md) for full exploit code.

Parser Stack Overflow (Unchecked memcpy)

Pattern: Custom file parser (PCAP, image, archive) allocates fixed stack buffer but input records can exceed it. memcpy copies before length validation, overflowing saved registers and return address. Must restore callee-saved registers: rbx to readable memory (BSS), loop counters to exit values, then ret gadget + win function. See [overflow-basics.md](overflow-basics.md#parser-stack-overflow-via-unchecked-memcpy-length-metactf-flash-2026).

Struct Pointer Overwrite (Heap Menu Challenges)

Pattern: Menu create/modify/delete on structs with data buffer + pointer. Overflow name into pointer field with GOT address, then write win address via modify. See [overflow-basics.md](overflow-basics.md) for full exploit and GOT target selection table.

Signed Integer Bypass

Pattern: scanf("%d") without sign check; negative quantity * price = negative total, bypasses balance check. See [overflow-basics.md](overflow-basics.md).

Canary-Aware Partial Overflow

Pattern: Overflow valid flag between buffer and canary. Use ./ as no-op path padding for precise length. See [overflow-basics.md](overflow-basics.md) and [advanced.md](advanced.md) for full exploit chain.

Global Buffer Overflow (CSV Injection)

Pattern: Adjacent global variables; overflow via extra CSV delimiters changes filename pointer. See [overflow-basics.md](overflow-basics.md) and [advanced.md](advanced.md) for full exploit.

ROP Chain Building

Leak libc via puts@PLT(puts@GOT), return to vuln, stage 2 with system("/bin/sh"). See [rop-and-shellcode.md](rop-and-shellcode.md) for full two-stage ret2libc pattern, leak parsing, and return target selection.

DynELF libc discovery: pwntools.DynELF(leak_func, pointer_in_libc) resolves libc symbols remotely without knowing the libc version. See [rop-and-shellcode.md](rop-and-shellcode.md#dynelf-automated-libc-discovery-rc3-ctf-2016).

Constrained shellcode in small buffers: When buffer is too small, use read() shellcode stub (< 20 bytes) to pull full stage-2 shellcode. See [rop-and-shellcode.md](rop-and-shellcode.md#constrained-shellcode-in-small-buffers-tum-ctf-2016).

Raw syscall ROP: When system()/execve() crash (CET/IBT), use pop rax; ret + syscall; ret from libc. See [rop-and-shellcode.md](rop-and-shellcode.md).

ret2csu: __libc_csu_init gadgets control rdx, rsi, edi and call any GOT function — universal 3-argument call without libc gadgets. See [rop-and-shellcode.md](rop-and-shellcode.md#ret2csu--__libc_csu_init-gadgets-crypto-cat).

Bad char XOR bypass: XOR payload data with key before writing to .data, then XOR back in place with ROP gadgets. Avoids null bytes, newlines, and other filtered characters. See [rop-and-shellcode.md](rop-and-shellcode.md#bad-character-bypass-via-xor-encoding-in-rop-crypto-cat).

Exotic gadgets (BEXTR/XLAT/STOSB/PEXT): When standard mov write gadgets are unavailable, chain obscure x86 instructions for byte-by-byte memory writes. See [rop-and-shellcode.md](rop-and-shellcode.md#exotic-x86-gadgets--bextrxlatstosbpext-crypto-cat).

Stack pivot (xchg rax,esp): Swap stack pointer to attacker-controlled heap/buffer when overflow is too small for full ROP chain. Requires pop rax; ret to load pivot address first. See [rop-and-shellcode.md](rop-and-shellcode.md#stack-pivot-via-xchg-raxesp-crypto-cat).

rdx control: After puts(), rdx is clobbered to 1. Use pop rdx; pop rbx; ret from libc, or re-enter binary's read setup + stack pivot. See [rop-and-shellcode.md](rop-and-shellcode.md).

Canary XOR epilogue as rdx zeroing gadget: When no pop rdx; ret exists, jump into the canary check epilogue xor rdx, fs:28h -- it zeros RDX when the canary is intact. See [rop-and-shellcode.md](rop-and-shellcode.md#stack-canary-xor-epilogue-as-rdx-zeroing-gadget-volgactf-2017).

stub_execveat as execve alternative: When no pop rax; ret exists, use stub_execveat (syscall 322/0x142) instead of execve -- send exactly 0x142 bytes so read() return value sets rax. See [rop-and-shellcode.md](rop-and-shellcode.md#stub_execveat-syscall-as-execve-alternative-asis-ctf-2018).

Shell interaction: After execve, sleep(1) then sendline(b'cat /flag*'). See [rop-and-shellcode.md](rop-and-shellcode.md).

Format String Through Input Transformation

ROT13-encoded format string: When input is ROT13/Caesar-transformed before reaching printf, pre-encode the format string payload with the inverse transform so it arrives intact. See [format-string.md](format-string.md#format-string-exploit-through-rot13-encoding-sunshinectf-2018).

Kernel Exploitation

addr_limit bypass via failed file open: When a kernel module sets addr_limit = KERNEL_DS but fails to restore it on error paths, force the error (e.g., make target file a directory) to retain kernel memory access from userspace read()/write(). See [kernel-techniques.md](kernel-techniques.md#kernel-addr_limit-bypass-via-failed-file-open-midnight-sun-ctf-2018).

Sandbox and Emulator Escape

CPU emulator eval injection: When an emulator's print opcode uses eval('"' + buf + '"') for escape sequences, build "+__import__("os").system("cmd")# in emulator memory via ADD opcodes to escape the string and execute Python. See [sandbox-escape.md](sandbox-escape.md#cpu-emulator-print-opcode-python-eval-injection-midnight-sun-ctf-2018).

Advanced Exploit Primitives

Neural network function pointer OOB: When a binary uses NN output as an index into a function pointer array without bounds checking, retrain weights/biases to produce an out-of-bounds index that reads a target address from the biases array. See [advanced-exploits-4.md](advanced-exploits-4.md#neural-network-output-as-function-pointer-index-oob-swampctf-2018).

Shellcode unique-byte limit bypass via counter overflow: When shellcode is limited to N unique bytes, spray the stack to corrupt the seen[256] counter, then re-execute main (skipping memset) so the overflowed counter allows arbitrary bytes on the second run. See [advanced-exploits-4.md](advanced-exploits-4.md#shellcode-unique-byte-limit-bypass-via-counter-overflow-blaze-ctf-2018).

Deep-Dive Notes

Use [field-notes.md](field-notes.md) once you have confirmed the challenge is truly exploitation-heavy.

• Heap and allocator notes: House of Apple, tcache, unsafe unlink, talloc, UAF, FSOP
• Advanced exploit notes: seccomp bypass, ret2vdso, io_uring, integer truncation, ASAN, timing oracles
• Sandbox and hybrid notes: pyjail crossover, busybox escapes, custom VMs, shell tricks, path sanitizers
• Kernel and Windows notes: kernel playbooks, SEH, CFG bypass, privilege escalation
• Historical case notes: older but still reusable CTF exploit patterns