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 ropper ROPgadget

Linux (apt):

apt install gdb binutils strace ltrace qemu-system-x86

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

Additional Resources

• 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 - 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
• 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
• 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)
• 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 - 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
• 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 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 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
• 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
• sandbox-escape.md - Custom VM exploitation, FUSE/CUSE devices, busybox/restricted shell, shell tricks, process_vm_readv sandbox bypass, named pipe file size bypass (cross-references ctf-misc/pyjails.md for Python jail techniques)
• 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 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)
• 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

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

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(). See overflow-basics.md for full exploit code.

Stack alignment: Modern glibc needs 16-byte alignment; SIGSEGV in movaps = add extra ret gadget. See overflow-basics.md.

Offset calculation: Buffer at rbp - N, return at rbp + 8, total = N + 8. See overflow-basics.md.

Input filtering: memmem() checks block certain byte sequences; assert payload doesn't contain banned strings. See overflow-basics.md.

Finding gadgets: ROPgadget --binary binary | grep "pop rdi", or use pwntools ROP() which also finds hidden gadgets in CMP immediates. See overflow-basics.md.

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.

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 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.

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 and 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 and 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 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.

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.

Raw syscall ROP: When system()/execve() crash (CET/IBT), use pop rax; ret + syscall; ret from libc. See 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.

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.

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.

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.

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.

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

ret2vdso — No-Gadget Binary Exploitation

Pattern: Statically-linked binary with minimal functions and no useful ROP gadgets. The Linux kernel maps a vDSO into every process, containing usable gadgets. Leak vDSO base from AT_SYSINFO_EHDR (auxv type 0x21) on the stack, dump the vDSO, extract gadgets for execve. vDSO is kernel-specific — always dump the remote copy. See rop-advanced.md.

Use-After-Free (UAF) Exploitation

Pattern: Menu create/delete/view where free() doesn't NULL pointer. Create -> leak -> free -> allocate same-size object to overwrite function pointer -> trigger callback. Key: both structs must be same size for tcache reuse. See advanced.md for full exploit code.

Seccomp Bypass

Alternative syscalls when seccomp blocks open()/read(): openat() (257), openat2() (437, often missed!), sendfile() (40), readv()/writev(), mmap() (9, map flag file into memory instead of read), pread64() (17).

Check rules: seccomp-tools dump ./binary

See rop-advanced.md for quick reference and advanced.md for conditional buffer address restrictions, shellcode without relocations, scmp_arg_cmp struct layout.

Stack Shellcode with Input Reversal

Pattern: Binary reverses input buffer. Pre-reverse shellcode, use partial 6-byte RIP overwrite, trampoline jmp short to NOP sled. See rop-advanced.md.

.fini_array Hijack

Writable .fini_array + arbitrary write -> overwrite with win/shellcode address. Works even with Full RELRO. See rop-advanced.md for implementation.

Path Traversal Sanitizer Bypass

Pattern: Sanitizer skips char after banned char match; double chars to bypass (e.g., ....//....//etc//passwd). Also try /proc/self/fd/3 if binary has flag fd open. See advanced.md.

Kernel Exploitation

modprobe_path overwrite (smallkirby/kernelpwn): Overwrite modprobe_path with evil script path, then execve a binary with non-printable first 4 bytes. Kernel runs the script as root. Requires AAW; blocked by CONFIG_STATIC_USERMODEHELPER. See kernel.md.

tty_struct kROP (smallkirby/kernelpwn): open("/dev/ptmx") allocates tty_struct in kmalloc-1024. Overwrite ops with fake vtable → ioctl() hijacks RIP. Build two-phase kROP within tty_struct itself via leave gadget stack pivot. See kernel.md.

userfaultfd race stabilization (smallkirby/kernelpwn): Register mmap'd region with uffd. Kernel page fault blocks the thread → deterministic race window for heap manipulation. See kernel.md.

Heap spray structures: tty_struct (kmalloc-1024, kbase leak), tty_file_private (kmalloc-32, kheap leak), poll_list (variable, arbitrary free via linked list), user_key_payload (variable, add_key() controlled data), seq_operations (kmalloc-32, kbase leak). See kernel.md.

ret2usr (hxp CTF 2020): When SMEP/SMAP are disabled, call prepare_kernel_cred(0) → commit_creds() directly from userland function, then swapgs; iretq to return as root. See kernel.md.

Kernel ROP chain (hxp CTF 2020): With SMEP, build ROP: pop rdi; ret → 0 → prepare_kernel_cred → mov rdi, rax → commit_creds → swapgs → iretq → userland. See kernel.md.

KPTI bypass methods (hxp CTF 2020): Four approaches: swapgs_restore_regs_and_return_to_usermode + 22 trampoline, SIGSEGV signal handler, modprobe_path overwrite via ROP, core_pattern pipe via ROP. See kernel.md.

FGKASLR bypass (hxp CTF 2020): Early .text section gadgets are unaffected. Resolve randomized functions via __ksymtab relative offsets in multi-stage exploit. See kernel.md.

Config recon: Check QEMU script for SMEP/SMAP/KASLR/KPTI. Detect FGKASLR via readelf -S vmlinux section count (30 vs 36000+). Check CONFIG_KALLSYMS_ALL via grep modprobe_path /proc/kallsyms. See kernel.md.

OOB via vulnerable lseek, heap grooming with fork(), SUID exploits. Check CONFIG_SLAB_FREELIST_RANDOM and CONFIG_SLAB_MERGE_DEFAULT. See advanced.md.

Race window extension (DiceCTF 2026): MADV_DONTNEED + mprotect() loop forces repeated page faults during kernel operations touching userland memory, extending race windows from sub-ms to tens of seconds. See kernel-techniques.md.

Cross-cache via CPU split (DiceCTF 2026): Allocate on CPU 0, free from CPU 1 — objects escape dedicated SLUB caches via partial list overflow → buddy allocator. See kernel-techniques.md.

PTE overlap file write (DiceCTF 2026): Reclaim freed page as PTE page, overlap anonymous + file-backed mappings → write through anonymous side modifies file content at physical page level. See kernel-techniques.md.

io_uring UAF with SQE Injection

Pattern: Custom slab allocator + io_uring worker thread. FLUSH frees objects (UAF), type confusion via slab fallback, craft IORING_OP_OPENAT SQE in reused memory. io_uring trusts SQE contents from userland shared memory. See advanced-exploits-2.md.

Integer Truncation Bypass (int32→int16)

Pattern: Input validated as int32 (>= 0), cast to int16_t for bounds check. Value 65534 passes int32 check, becomes -2 as int16_t → OOB array access. Use xchg rdi, rax; cld; ret gadget for dynamic fd capture in containerized ORW chains. See advanced-exploits-2.md.

Format String Quick Reference

• Leak stack: %p.%p.%p.%p.%p.%p | Leak specific: %7$p
• Write: %n (4-byte), %hn (2-byte), %hhn (1-byte), %lln (8-byte full 64-bit)
• GOT overwrite for code execution (Partial RELRO required)

See format-string.md for GOT overwrite patterns, blind pwn, filter bypass, canary+PIE leak, __free_hook overwrite, and argument retargeting.

.rela.plt / .dynsym Patching (Format String)

When to use: GOT addresses contain bad bytes (e.g., 0x0a). Patch .rela.plt symbol index + .dynsym st_value to redirect function resolution to win(). Bypasses all GOT byte restrictions. See format-string.md for full technique and code.

Heap Exploitation

• tcache poisoning (glibc 2.26+), fastbin dup / double free
• House of Force (old glibc), unsorted bin attack
• House of Apple 2 (glibc 2.34+): FSOP (File Stream Oriented Programming) via _IO_wfile_jumps when __free_hook/__malloc_hook removed. Fake FILE with _flags = " sh", vtable chain → system(fp). For SUID binaries: use setcontext() variant to stack pivot → setuid(0) → system() (dash drops privs when uid != euid). See heap-techniques.md.
• Classic unlink: Corrupt adjacent chunk metadata, trigger backward consolidation for write-what-where primitive. Pre-2.26 glibc only. See heap-techniques.md.
• House of Force: Corrupt top chunk size to 0xffffffffffffffff, next malloc(target - top - 2*SIZE_SZ) returns arbitrary address. Pre-2.29 glibc only. See heap-techniques.md.
• House of Einherjar: Off-by-one null clears PREV_INUSE, backward consolidation with self-pointing unlink.
• Safe-linking (glibc 2.32+): tcache fd mangled as ptr ^ (chunk_addr >> 12).
• Check glibc version: strings libc.so.6 | grep GLIBC
• Freed chunks contain libc pointers (fd/bk) -> leak via error messages or missing null-termination
• Heap feng shui: control alloc order/sizes, create holes, place targets adjacent to overflow source
• Unsafe unlink + top chunk consolidation: After unlink writes self-pointer to BSS, craft fake BSS chunk spanning to top chunk. free() consolidates, relocating heap base to BSS. Subsequent mallocs return BSS memory. See heap-techniques.md.

House of Orange: Corrupt top chunk size → large malloc forces sysmalloc → old top freed without calling free(). Chain with FSOP. See heap-techniques.md.

House of Spirit: Forge fake chunk in target area, free() it, reallocate to get write access. Requires valid size + next chunk size. See heap-techniques.md.

House of Lore: Corrupt smallbin bk → link fake chunk → second malloc returns attacker-controlled address. See heap-techniques.md.

ret2dlresolve: Forge Elf64_Sym/Rela to resolve arbitrary libc function without leak. Ret2dlresolvePayload(elf, symbol="system", args=["/bin/sh"]). Requires Partial RELRO. See advanced.md.

tcache stashing unlink (glibc 2.29+): Corrupt smallbin chunk's bk during tcache stashing → arbitrary address linked into tcache → write primitive. See heap-techniques.md.

See heap-techniques.md for House of Apple 2 FSOP chain (+ setcontext SUID variant), House of Orange/Spirit/Lore/Force, tcache stashing unlink, custom allocator exploitation (nginx pools, talloc), classic unlink, musl libc heap. See advanced.md for ret2dlresolve, heap overlap via base conversion, tree data structure stack underallocation.

GF(2) Gaussian elimination for tcache poisoning: When a deterministic XOR cipher corrupts heap metadata as a side effect, model the corruption as linear algebra over GF(2). Find a subset of cipher seeds whose combined XOR transforms tcache fd from current value to target address. See advanced-exploits-4.md.

talloc Pool Header Forgery (Boston Key Party 2016)

Pattern: talloc (hierarchical allocator in Samba/CUPS) pool header forgery. Forge fake pool header with controlled end/object_count fields to redirect next talloc() to arbitrary address. Leak GOT for libc, write __free_hook with system(). See heap-techniques.md.

JIT Compilation Exploits

Pattern: Off-by-one in instruction encoding -> misaligned machine code. Embed shellcode as operand bytes of subtraction operations, chain with 2-byte jmp instructions. See advanced.md.

BF JIT unbalanced bracket: Unbalanced ] pops tape address (RWX) from stack → write shellcode to tape with +/-, trigger ] to jump to it. See advanced.md.

Type Confusion in Interpreters

Pattern: Interpreter sets wrong type tag → struct fields reinterpreted. Unused padding bytes in one variant become active pointers/data in another. Flag bytes as type value trigger UNKNOWN_DATA dump. See advanced.md.

Off-by-One Index / Size Corruption

Pattern: Array index 0 maps to entries[-1], overlapping struct metadata (size field). Corrupted size → OOB read leaks canary/libc, then OOB write places ROP chain. See advanced.md.

Double win() Call

Pattern: win() checks if (attempts++ > 0) — needs two calls. Stack two return addresses: p64(win) + p64(win). See advanced.md.

Arbitrary Read/Write to Shell via GOT Overwrite (BSidesSF 2026)

Pattern: Binary provides explicit read/write primitives. Leak libc via GOT read, overwrite strtoll@GOT with system, next call becomes system(user_input). Choose GOT targets where the function takes a user-controlled string as first arg. See advanced-exploits-3.md.

Stack Leak via __environ and memcpy Overflow (BSidesSF 2026)

Pattern: Binary with read-only primitive and memcpy(stack_buf, user_addr, user_len). Leak libc via GOT, leak stack via __environ, plant ROP addresses in input buffer, overflow memcpy to copy them over return address, send EOF to trigger return. See advanced-exploits-3.md.

JIT Sandbox Escape via uint16 Jump Truncation (BSidesSF 2026)

Pattern: JIT compiler truncates conditional jump offset to uint16, causing misalignment when code exceeds 64KB. Embed 2-byte shellcode fragments in add immediates, thread with jmp $+3 to chain execution. See advanced-exploits-3.md.

DNS Compression Pointer Stack Overflow (BSidesSF 2026)

Pattern: Custom DNS server doesn't track decompressed name length. Compression pointer chains revisit data, overflowing stack buffer. Split ROP chain across multiple DNS question entries. See advanced-exploits-3.md.

ELF Code Signing Bypass via Program Headers (BSidesSF 2026)

Pattern: Signing scheme hashes section headers/content but not program headers. Append shellcode, modify LOAD segment's p_offset to point to appended data — signature still valid, loader executes attacker code. See advanced-exploits-3.md.

Game Level Format Signed/Unsigned Coordinate Mismatch (BSidesSF 2026)

Pattern: Level editor parses signed integer coordinates but bounds-checks via unsigned comparison — negative coordinates pass the check and write block IDs (arbitrary bytes) before the level array, enabling stack return address overwrite. Leak stack address via hidden developer mode, encode shellcode as block IDs. See advanced-exploits-3.md.

File Descriptor Inheritance via Missing O_CLOEXEC (BSidesSF 2026)

Pattern: Service reads secret into memfd_create() FD without MFD_CLOEXEC, then calls system() for user commands — child inherits the FD. Bypass strstr() keyword filters with shell quote splitting (p'r'oc instead of proc) to read /proc/self/fd/N. See advanced-exploits-3.md.

Sign Extension Integer Underflow in Metadata Parsing (BSidesSF 2026)

Pattern: Metadata parser's to_int32 converts unsigned values >= 0x80000000 to negative signed integers. Used as array index/offset, this causes OOB memory access. Iterate byte-by-byte to leak flag from memory. See advanced-exploits-3.md.

ROP Chain Construction with Read-Only Primitive (BSidesSF 2026)

Pattern: Binary with only read() primitive — no write, no win function. Leak libc via GOT, then "import" arbitrary byte values onto the stack by reading from libc offsets whose content matches desired ROP gadget addresses. Read primitive doubles as write primitive. See advanced-exploits-3.md.

Esoteric Language GOT Overwrite

Pattern: Brainfuck/Pikalang interpreter with unbounded tape = arbitrary read/write relative to buffer base. Move pointer to GOT, overwrite byte-by-byte with system(). See advanced.md.

Protocol Stack Bleeding

Custom network protocols echoing data based on length field leak stack memory when length exceeds actual data (Heartbleed-style). See overflow-basics.md.

Timing Attack Flag Recovery

Validation time varies per correct character; measure elapsed time per candidate byte to recover flag character-by-character. See advanced-exploits.md.

DNS Record Buffer Overflow

Pattern: Many AAAA records overflow stack buffer in DNS response parser. Set up DNS server with excessive records, overwrite return address. See advanced.md.

ASAN Shadow Memory Exploitation

Pattern: Binary with AddressSanitizer has format string + OOB write. ASAN may use "fake stack" (50% chance). Leak PIE, detect real vs fake stack, calculate OOB write offset to overwrite return address. See advanced.md.

Format String .fini_array Loop for Multi-Stage Exploitation (Codegate 2016)

Pattern: No GOT function called after printf(). Overwrite .fini_array[0] with main() for re-execution loop. Stage 1: leak libc/stack. Stage 2: printf@GOT to system(), __stack_chk_fail@GOT to main(). Stage 3: corrupt canary to trigger __stack_chk_fail re-entry, now printf(input) is system(input). See format-string.md.

Format String with RWX .fini_array Hijack

Pattern (Encodinator): Base85-encoded input in RWX memory passed to printf(). Write shellcode to RWX region, overwrite .fini_array[0] via format string %hn writes. Use convergence loop for base85 argument numbering. See advanced.md.

Custom Canary Preservation

Pattern: Buffer overflow must preserve known canary value. Write exact canary bytes at correct offset: b'A' * 64 + b'BIRD' + b'X'. See advanced.md.

MD5 Preimage Gadget Construction

Pattern (Hashchain): Brute-force MD5 preimages with eb 0c prefix (jmp +12) to skip middle bytes; bytes 14-15 become 2-byte i386 instructions. Build syscall chains from gadgets like 31c0 (xor eax), cd80 (int 0x80). See advanced.md for C code and v2 technique.

Python Sandbox Escape

AST bypass via f-strings, audit hook bypass with b'flag.txt' (bytes vs str), MRO-based __builtins__ recovery. See sandbox-escape.md.

VM GC-Triggered UAF (Slab Reuse)

Pattern: Custom VM with NEWBUF/SLICE/GC opcodes. Slicing creates shared slab reference; dropping+GC'ing slice frees slab while parent still holds it. Allocate function object to reuse slab, leak code pointer via UAF read, overwrite with win() address. See advanced.md.

GC Null-Reference Cascading Corruption

Pattern: Mark-compact GC follows null references to heap address 0, creating fake object. During compaction, memmove cascades corruption through adjacent object headers → OOB access → libc leak → FSOP. See advanced.md.

OOB Read via Stride/Rate Leak

Pattern: String processing function with user-controlled stride skips past null terminator, leaking stack canary and return address one byte at a time. Then overflow with leaked values. See overflow-basics.md.

SROP with UTF-8 Constraints

Pattern: When payload must be valid UTF-8 (Rust binaries, JSON parsers), use SROP — only 3 gadgets needed. Multi-byte UTF-8 sequences spanning register field boundaries "fix" high bytes. See rop-advanced.md.

VM Exploitation (Custom Bytecode)

Pattern: Custom VM with OOB read/write in syscalls. Leak PIE via XOR-encoded function pointer, overflow to rewrite pointer with win() ^ KEY. See sandbox-escape.md.

FUSE/CUSE Character Device Exploitation

Look for cuse_lowlevel_main() / fuse_main(), backdoor write handlers with command parsing. Exploit to chmod /etc/passwd then modify for root access. See sandbox-escape.md.

Busybox/Restricted Shell Escalation

Find writable paths via character devices, target /etc/passwd or /etc/sudoers, modify permissions then content. See sandbox-escape.md.

process_vm_readv Sandbox Bypass (0CTF 2016)

Pattern: Sandbox validates file paths via process_vm_readv() + realpath(). Map memory with PROT_READ only at fixed address via mmap(MAP_FIXED) -- sandbox's process_vm_readv fails silently, bypassing path validation entirely. See sandbox-escape.md.

Named Pipe (mkfifo) File Size Bypass (Nuit du Hack 2016)

Pattern: Binary checks stat() file size before reading. Named pipes report st_size = 0 but deliver arbitrary data via read(). mkfifo /tmp/pipe && cat payload > /tmp/pipe & then pass pipe to binary. Combine with ln -s /flag arena.c for string reuse in ROP. See sandbox-escape.md.

Shell Tricks

exec<&3;sh>&3 for fd redirection, $0 instead of sh, ls -la /proc/self/fd to find correct fd. See sandbox-escape.md.

Double Stack Pivot to BSS via leave;ret (Midnightflag 2026)

Pattern: Small overflow (only RBP + RIP). Overwrite RBP → BSS address, RIP → leave; ret gadget. leave sets RSP = RBP (BSS). Second stage at BSS calls fgets(BSS+offset, large_size, stdin) to load full ROP chain. See rop-advanced.md.

RETF Architecture Switch for Seccomp Bypass (Midnightflag 2026)

Pattern: Seccomp blocks 64-bit syscalls (open, execve). Use retf gadget to load CS=0x23 (IA-32e compatibility mode). In 32-bit mode, int 0x80 uses different syscall numbers (open=5, read=3, write=4) not covered by the filter. Requires mprotect to make BSS executable for 32-bit shellcode. See rop-advanced.md.

Leakless Libc via Multi-fgets stdout FILE Overwrite (Midnightflag 2026)

Pattern: No libc leak available. Chain multiple fgets(addr, 7, stdin) calls via ROP to construct fake stdout FILE struct on BSS. Set _IO_write_base to GOT entry, call fflush(stdout) → leaks GOT content → libc base. The 7-byte writes avoid null byte corruption since libc pointer MSBs are already \x00. See advanced-exploits-2.md.

Signed/Unsigned Char Underflow → Heap Overflow (Midnightflag 2026)

Pattern: Size field stored as signed char, cast to unsigned char for use. size = -112 → (unsigned char)(-112) = 144, overflowing a 127-byte buffer by 17 bytes. Combine with XOR keystream brute-force for byte-precise writes, forge chunk sizes for unsorted bin promotion (libc leak), FSOP stdout for TLS leak, and TLS destructor (__call_tls_dtors) overwrite for RCE. See advanced-exploits-2.md.

TLS Destructor Hijack via __call_tls_dtors

Pattern: Alternative to House of Apple 2 on glibc 2.34+. Forge __tls_dtor_list entries with pointer-guard-mangled function pointers: encoded = rol(target ^ pointer_guard, 0x11). Requires leaking pointer guard from TLS segment (via FSOP stdout redirection). Each node calls PTR_DEMANGLE(func)(obj) on exit. See advanced-exploits-2.md.

Signed Int Overflow → Negative OOB Heap Write (Midnight 2026)

Pattern (Canvas of Fear): Index formula y * width + x in signed 32-bit int overflows to negative value, passing bounds check and writing backward into heap metadata. Use to corrupt adjacent chunk sizes/pointers, leak libc via unsorted bin, redirect a data pointer to environ for stack leak, then write ROP chain to main's return address. When binary is behind a web API, chain XSS → Fetch API → heap exploit, and inject \n in API parameters for command stacking via sendline().

See advanced-exploits-2.md for full exploit chain, XSS bridge pattern, and RGB pixel write primitive.

Custom Shadow Stack Bypass via Pointer Overflow (Midnight 2026)

Pattern (Revenant): Userland shadow stack in .bss with unbounded pointer. Recurse to advance shadow_stack_ptr past the array into user-controlled memory (e.g., username buffer), write win() there, then overflow the hardware stack return address to match. Both checks pass.

# Iterate (target_addr - shadow_stack_base) // 8 times to overflow pointer
for i in range(512):
    io.sendlineafter(b"Survivor name:\n", fit(exe.symbols["win"]))
    io.sendlineafter(b"[0] Flee", b"4")  # recurse

See advanced-exploits-2.md for full exploit and .bss layout analysis.

Windows SEH Overwrite + VirtualAlloc ROP (RainbowTwo HTB)

Format string leak defeats ASLR. SEH (Structured Exception Handler) overwrite with stack pivot to ROP chain. pushad builds VirtualAlloc call frame for DEP (Data Execution Prevention) bypass. Detached process launcher for shell stability on thread-based servers. See advanced-exploits-4.md.

SeDebugPrivilege → SYSTEM

SeDebugPrivilege + Meterpreter migrate -N winlogon.exe -> SYSTEM. See advanced-exploits-4.md.

mmap/munmap Size Mismatch UAF (0CTF 2017)

Over-unmap via mmap(small)/munmap(large) destroys adjacent mappings. Thread stack fills gap, old buffer pointer becomes write-into-stack. Race-free UAF variant. See advanced-exploits-4.md.

strcspn Indirect Null Byte Injection (BSidesSF 2017)

strcspn(buf, "\r\n") + null write truncates strings at injected newlines. Bypasses CGI null-byte filtering for path traversal. See advanced-exploits-4.md.

Useful Commands

checksec, one_gadget, ropper, ROPgadget, seccomp-tools dump, strings libc | grep GLIBC. See rop-advanced.md for full command list and pwntools template.