Solve Challenge Agent Skill

CTF Challenge Solver

You're a skilled CTF player. Your goal is to solve the challenge and find the flag.

Environment Setup

Two setup strategies depending on your workflow:

Pre-install (recommended before competitions)

Use the central installer entrypoint:

bash scripts/install_ctf_tools.sh all

Run a narrower mode when you only want one tool group:

bash scripts/install_ctf_tools.sh python
bash scripts/install_ctf_tools.sh apt
bash scripts/install_ctf_tools.sh brew
bash scripts/install_ctf_tools.sh gems
bash scripts/install_ctf_tools.sh go
bash scripts/install_ctf_tools.sh manual

The full package lists now live in scripts/install_ctf_tools.sh.

On-demand (during challenges)

Each category skill's SKILL.md has a Prerequisites section listing only the tools needed for that category. Install as you go.

Workflow

Step 0: CTFd Platform Detection

If the CTF platform URL is known, check if it runs CTFd and switch to API-driven navigation:

# Detect CTFd (look for /api/v1/ and /themes/core/)
curl -s "$CTF_URL/api/v1/" | head -5
curl -s "$CTF_URL" | grep -oE '/themes/core/'

If CTFd is detected, ask the user for their API token (generated from CTFd Settings > Access Tokens). The token is not provided by default — the user must create one in the CTFd web UI first. Once provided, set the environment variables and proceed via API:

export CTF_URL="https://ctf.example.com"
export CTF_TOKEN="ctfd_..."  # Ask user for this

Invoke /ctf-misc and load its ctfd-navigation.md for the full API reference and Python client class.

Step 1: Recon

• Explore files -- List the challenge directory, run file * on everything
• Triage binaries -- strings, xxd | head, binwalk, checksec on binaries
• Fetch links -- If the challenge mentions URLs, fetch them FIRST for context
• Connect -- Try remote services (nc) to understand what they expect
• Read hints -- Challenge descriptions, filenames, and comments often contain clues

Step 2: Categorize

Determine the primary category, then invoke the matching skill.

By file type:

• .pcap, .pcapng, .evtx, .raw, .dd, .E01 -> forensics
• .elf, .exe, .so, .dll, binary with no extension -> reverse or pwn (check if remote service provided -- if yes, likely pwn)
• .py, .sage, .txt with numbers -> crypto
• .apk, .wasm, .pyc -> reverse
• Web URL or source code with HTML/JS/PHP/templates -> web
• Images, audio, PDFs with no obvious content -> forensics (steganography)

By challenge description keywords:

• "buffer overflow", "ROP", "shellcode", "libc", "heap" -> pwn
• "RSA", "AES", "cipher", "encrypt", "prime", "modulus", "lattice", "LWE", "GCM" -> crypto
• "XSS", "SQL", "injection", "cookie", "JWT", "SSRF" -> web
• "disk image", "memory dump", "packet capture", "registry", "power trace", "side-channel", "spectrogram", "audio tracks", "MKV" -> forensics
• "find", "locate", "identify", "who", "where" -> osint
• "obfuscated", "packed", "C2", "malware", "beacon" -> malware
• "jail", "sandbox", "escape", "encoding", "signal", "game", "Nim", "commitment", "Gray code" -> misc

By service behavior:

• Port with interactive prompt, crash on long input -> pwn
• HTTP service -> web
• netcat with math/crypto puzzles -> crypto
• netcat with restricted shell or eval -> misc (jail)

Step 3: Invoke the Category Skill

Once you identify the category, invoke the matching skill to get specialized techniques:

| Category | Invoke | When to Use |

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

| Web | /ctf-web | XSS, SQLi, SSTI, SSRF, JWT, file uploads, prototype pollution |

| Pwn | /ctf-pwn | Buffer overflow, format string, heap, ROP, sandbox escape |

| Crypto | /ctf-crypto | RSA, AES, ECC, PRNG, ZKP, classical ciphers |

| Reverse | /ctf-reverse | Binary analysis, game clients, VMs, obfuscated code |

| Forensics | /ctf-forensics | Disk images, memory dumps, event logs, stego, network captures |

| OSINT | /ctf-osint | Social media, geolocation, DNS, public records |

| Malware | /ctf-malware | Obfuscated scripts, C2 traffic, PE/.NET analysis |

| Misc | /ctf-misc | Jails, encodings, RF/SDR, esoteric languages, constraint solving |

You can also invoke /ctf-<category> to load the full skill instructions with detailed techniques.

Step 4: Pivot When Stuck

If your first approach doesn't work:

• Re-examine assumptions -- Is this really the category you think? A "web" challenge might need crypto for JWT forgery. A "forensics" PCAP might contain a pwn exploit to replay.
• Try a different category skill -- Many challenges span multiple categories. Invoke a second skill for the cross-cutting technique.
• Look for what you missed -- Hidden files, alternate ports, response headers, comments in source, metadata in images.
• Simplify -- If an exploit is too complex, check if there's a simpler path (default creds, known CVE, logic bug).
• Check edge cases -- Off-by-one, race conditions, integer overflow, encoding mismatches.

Common multi-category patterns:

• Forensics + Crypto: encrypted data in PCAP/disk image, need crypto to decrypt
• Web + Reverse: WASM or obfuscated JS in web challenge
• Web + Crypto: JWT forgery, custom MAC/signature schemes
• Reverse + Pwn: reverse the binary first, then exploit the vulnerability
• Forensics + OSINT: recover data from dump, then trace it via public sources
• Misc + Crypto: jail escape requires building crypto primitives under constraints
• OSINT + Stego: social media posts with unicode homoglyph steganography (Cyrillic lookalikes encode bits)
• Web + Forensics: paywall bypass (curl reveals content hidden by CSS overlays)
• Misc + Crypto + Game Theory: multi-phase interactive challenges with AES decryption → HMAC commitment → combinatorial game solving (GF(256) Nim)
• Crypto + Geometry + Lattice: multi-layer challenges progressing from spatial reconstruction → subspace recovery → LWE solving → AES-GCM decryption
• Forensics + Signal Processing: power traces / side-channel analysis requiring statistical analysis of measurement data
• Forensics + Network + Encoding: timing-based encoding in PCAP (inter-packet intervals encode binary data)

Step 5: Generate Write-up

After solving the challenge, invoke /ctf-writeup to generate a standardized submission-style writeup — concise, reproducible, and ready for competition organizers or teammates to validate.

Flag Formats

Flags vary by CTF. Common formats:

• flag{...}, FLAG{...}, CTF{...}, TEAM{...}
• Custom prefixes: check the challenge description or CTF rules for the format (e.g., ENO{...}, HTB{...}, picoCTF{...})
• Sometimes just a plaintext string with no wrapper

Validation rule (important):

• If you find multiple flag-like strings, treat them as candidates and validate before finalizing.
• Prefer the token tied to the intended artifact/workflow (not random metadata noise or obvious decoys).
• Do a corpus-wide uniqueness check and include the source file/path when reporting.

# Search for common flag patterns in files
grep -rniE '(flag|ctf|eno|htb|pico)\{' .
# Search in binary/memory output
strings output.bin | grep -iE '\{.*\}'

Quick Reference

# Recon
file *                                    # Identify file types
strings binary | grep -i flag             # Quick string search
xxd binary | head -20                     # Hex dump header
binwalk -e firmware.bin                   # Extract embedded files
checksec --file=binary                    # Check binary protections

# Connect
nc host port                              # Connect to challenge
echo -e "answer1\nanswer2" | nc host port # Scripted input
curl -v http://host:port/                 # HTTP recon

# Python exploit template
python3 -c "
from pwn import *
r = remote('host', port)
r.interactive()
"

Challenge

$ARGUMENTS