FFUF (Fuzz Faster U Fool) Skill

Overview

FFUF is a fast web fuzzer written in Go, designed for discovering hidden content, directories, files, subdomains, and testing for vulnerabilities during penetration testing. It's significantly faster than traditional tools like dirb or dirbuster.

Installation

Using Go

go install github.com/ffuf/ffuf/v2@latest

Using Homebrew (macOS)

brew install ffuf

Binary download

Download from: https://github.com/ffuf/ffuf/releases/latest

Core Concepts

The FUZZ Keyword

The FUZZ keyword is used as a placeholder that gets replaced with entries from your wordlist. You can place it anywhere:

URLs: https://target.com/FUZZ
Headers: -H "Host: FUZZ"
POST data: -d "username=admin&password=FUZZ"
Multiple locations with custom keywords: -w wordlist.txt:CUSTOM then use CUSTOM instead of FUZZ

Multi-wordlist Modes

clusterbomb: Tests all combinations (default) - cartesian product
pitchfork: Iterates through wordlists in parallel (1-to-1 matching)
sniper: Tests one position at a time (for multiple FUZZ positions)

Common Use Cases

Directory and File Discovery

Basic directory fuzzing

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ

With file extensions

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -e .php,.html,.txt,.pdf

Colored and verbose output

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -c -v

With recursion (finds nested directories)

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -recursion -recursion-depth 2

Subdomain Enumeration

Virtual host discovery

ffuf -w /path/to/subdomains.txt -u https://target.com -H "Host: FUZZ.target.com" -fs 4242

Note: -fs 4242 filters out responses of size 4242 (adjust based on default response size)

Parameter Fuzzing

GET parameter names

ffuf -w /path/to/params.txt -u https://target.com/script.php?FUZZ=test_value -fs 4242

GET parameter values

ffuf -w /path/to/values.txt -u https://target.com/script.php?id=FUZZ -fc 401

Multiple parameters

ffuf -w params.txt:PARAM -w values.txt:VAL -u https://target.com/?PARAM=VAL -mode clusterbomb

POST Data Fuzzing

Basic POST fuzzing

ffuf -w /path/to/passwords.txt -X POST -d "username=admin&password=FUZZ" -u https://target.com/login.php -fc 401

JSON POST data

ffuf -w entries.txt -u https://target.com/api -X POST -H "Content-Type: application/json" -d '{"name": "FUZZ", "key": "value"}' -fr "error"

Fuzzing multiple POST fields

ffuf -w users.txt:USER -w passes.txt:PASS -X POST -d "username=USER&password=PASS" -u https://target.com/login -mode pitchfork

Header Fuzzing

Custom headers

ffuf -w /path/to/wordlist.txt -u https://target.com -H "X-Custom-Header: FUZZ"

Multiple headers

ffuf -w /path/to/wordlist.txt -u https://target.com -H "User-Agent: FUZZ" -H "X-Forwarded-For: 127.0.0.1"

Filtering and Matching

Matchers (Include Results)

-mc : Match status codes (default: 200-299,301,302,307,401,403,405,500)
-ml : Match line count
-mr : Match regex
-ms : Match response size
-mt : Match response time (e.g., >100 or <100 milliseconds)
-mw : Match word count

Filters (Exclude Results)

-fc : Filter status codes (e.g., -fc 404,403,401 )
-fl : Filter line count
-fr : Filter regex (e.g., -fr "error" )
-fs : Filter response size (e.g., -fs 42,4242 )
-ft : Filter response time
-fw : Filter word count

Auto-Calibration (USE BY DEFAULT!)

CRITICAL: Always use -ac unless you have a specific reason not to. This is especially important when having Claude analyze results, as it dramatically reduces noise and false positives.

Auto-calibration - ALWAYS USE THIS

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -ac

Per-host auto-calibration (useful for multiple hosts)

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -ach

Custom auto-calibration string (for specific patterns)

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -acc "404NotFound"

Why -ac is essential:

Automatically detects and filters repetitive false positive responses
Removes noise from dynamic websites with random content
Makes results analysis much easier for both humans and Claude
Prevents thousands of identical 404/403 responses from cluttering output
Adapts to the target's specific behavior

When Claude analyzes your ffuf results, -ac is MANDATORY - without it, Claude will waste time sifting through thousands of false positives instead of finding the interesting anomalies.

Rate Limiting and Timing

Rate Control

Limit to 2 requests per second (stealth mode)

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -rate 2

Add delay between requests (0.1 to 2 seconds random)

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -p 0.1-2.0

Set number of concurrent threads (default: 40)

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -t 10

Time Limits

Maximum total execution time (60 seconds)

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -maxtime 60

Maximum time per job (useful with recursion)

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -maxtime-job 60 -recursion

Output Options

Output Formats

JSON output

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -o results.json

HTML output

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -of html -o results.html

CSV output

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -of csv -o results.csv

All formats

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -of all -o results

Silent mode (no progress, only results)

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -s

Pipe to file with tee

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -s | tee results.txt

Advanced Techniques

Using Raw HTTP Requests (Critical for Authenticated Fuzzing)

This is one of the most powerful features of ffuf, especially for authenticated requests with complex headers, cookies, or tokens.

Workflow:

Capture a full authenticated request (from Burp Suite, browser DevTools, etc.)
Save it to a file (e.g., req.txt )
Replace the value you want to fuzz with the FUZZ keyword
Use the --request flag

From a file containing raw HTTP request

ffuf --request req.txt -w /path/to/wordlist.txt -ac

Example req.txt file:

POST /api/v1/users/FUZZ HTTP/1.1 Host: target.com User-Agent: Mozilla/5.0 Authorization: Bearer eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9... Cookie: session=abc123xyz; csrftoken=def456 Content-Type: application/json Content-Length: 27

{"action":"view","id":"1"}

Use Cases:

Fuzzing authenticated endpoints with complex auth headers
Testing API endpoints with JWT tokens
Fuzzing with CSRF tokens, session cookies, and custom headers
Testing endpoints that require specific User-Agents or Accept headers
POST/PUT/DELETE requests with authentication

Pro Tips:

You can place FUZZ in multiple locations: URL path, headers, body
Use -request-proto https if needed (default is https)
Always use -ac to filter out authenticated "not found" or error responses
Great for IDOR testing: fuzz user IDs, document IDs, etc. in authenticated contexts

Common authenticated fuzzing patterns

ffuf --request req.txt -w user_ids.txt -ac -mc 200 -o results.json

With multiple FUZZ positions using custom keywords

ffuf --request req.txt -w endpoints.txt:ENDPOINT -w ids.txt:ID -mode pitchfork -ac

Proxy Usage

HTTP proxy (useful for Burp Suite)

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -x http://127.0.0.1:8080

SOCKS5 proxy

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -x socks5://127.0.0.1:1080

Replay matched requests through proxy

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -replay-proxy http://127.0.0.1:8080

Cookie and Authentication

Using cookies

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -b "sessionid=abc123; token=xyz789"

Client certificate authentication

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -cc client.crt -ck client.key

Encoding

URL encoding

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -enc 'FUZZ:urlencode'

Multiple encodings

ffuf -w /path/to/wordlist.txt -u https://target.com/FUZZ -enc 'FUZZ:urlencode b64encode'

Testing for Vulnerabilities

SQL injection testing

ffuf -w sqli_payloads.txt -u https://target.com/page.php?id=FUZZ -fs 1234

XSS testing

ffuf -w xss_payloads.txt -u https://target.com/search?q=FUZZ -mr "<script>"

Command injection

ffuf -w cmdi_payloads.txt -u https://target.com/execute?cmd=FUZZ -fr "error"

Batch Processing Multiple Targets

Process multiple URLs

cat targets.txt | xargs -I@ sh -c 'ffuf -w wordlist.txt -u @/FUZZ -ac'

Loop through multiple targets with results

for url in $(cat targets.txt); do ffuf -w wordlist.txt -u $url/FUZZ -ac -o "results_$(echo $url | md5sum | cut -d' ' -f1).json" done

Best Practices

ALWAYS Use Auto-Calibration

Use -ac by default for every scan. This is non-negotiable for productive pentesting:

ffuf -w wordlist.txt -u https://target.com/FUZZ -ac

Use Raw Requests for Authentication

Don't struggle with command-line flags for complex auth. Capture the full request and use --request :

1. Capture authenticated request from Burp/DevTools

2. Save to req.txt with FUZZ keyword in place

3. Run with -ac

ffuf --request req.txt -w wordlist.txt -ac -o results.json

Use Appropriate Wordlists

Directory discovery: SecLists Discovery/Web-Content (raft-large-directories.txt, directory-list-2.3-medium.txt)
Subdomains: SecLists Discovery/DNS (subdomains-top1million-5000.txt)
Parameters: SecLists Discovery/Web-Content (burp-parameter-names.txt)
Usernames: SecLists Usernames
Passwords: SecLists Passwords
Source: https://github.com/danielmiessler/SecLists

Rate Limiting for Stealth

Use -rate to avoid triggering WAF/IDS or overwhelming the server:

ffuf -w wordlist.txt -u https://target.com/FUZZ -rate 2 -t 10

Filter Strategically

Check the default response first to identify common response sizes, status codes, or patterns
Use -fs to filter by size or -fc to filter by status code
Combine filters: -fc 403,404 -fs 1234

Save Results Appropriately

Always save results to a file for later analysis:

ffuf -w wordlist.txt -u https://target.com/FUZZ -o results.json -of json

Use Interactive Mode

Press ENTER during execution to drop into interactive mode where you can:

Adjust filters on the fly
Save current results
Restart the scan
Manage the queue

Recursion Depth

Be careful with recursion depth to avoid getting stuck in infinite loops or overwhelming the server:

ffuf -w wordlist.txt -u https://target.com/FUZZ -recursion -recursion-depth 2 -maxtime-job 120

Common Patterns and One-Liners

Quick Directory Scan

ffuf -w ~/wordlists/common.txt -u https://target.com/FUZZ -mc 200,301,302,403 -ac -c -v

Comprehensive Scan with Extensions

ffuf -w ~/wordlists/raft-large-directories.txt -u https://target.com/FUZZ -e .php,.html,.txt,.bak,.old -ac -c -v -o results.json

Authenticated Fuzzing (Raw Request)

1. Save your authenticated request to req.txt with FUZZ keyword

2. Run:

ffuf --request req.txt -w ~/wordlists/api-endpoints.txt -ac -o results.json -of json

API Endpoint Discovery

ffuf -w ~/wordlists/api-endpoints.txt -u https://api.target.com/v1/FUZZ -H "Authorization: Bearer TOKEN" -mc 200,201 -ac -c

Subdomain Discovery with Auto-Calibration

ffuf -w ~/wordlists/subdomains-top5000.txt -u https://FUZZ.target.com -ac -c -v

POST Login Brute Force

ffuf -w ~/wordlists/passwords.txt -X POST -d "username=admin&password=FUZZ" -u https://target.com/login -fc 401 -rate 5 -ac

IDOR Testing with Auth

Use req.txt with authenticated headers and FUZZ in the ID parameter

ffuf --request req.txt -w numbers.txt -ac -mc 200 -fw 100-200

Configuration File

Create ~/.config/ffuf/ffufrc for default settings:

[http] headers = ["User-Agent: Mozilla/5.0"] timeout = 10

[general] colors = true threads = 40

[matcher] status = "200-299,301,302,307,401,403,405,500"

Troubleshooting

Too Many False Positives

Use -ac for auto-calibration
Check default response and filter by size with -fs
Use regex filtering with -fr

Too Slow

Increase threads: -t 100
Reduce wordlist size
Use -ignore-body if you don't need response content

Getting Blocked

Reduce rate: -rate 2
Add delays: -p 0.5-1.5
Reduce threads: -t 10
Randomize User-Agent
Use proxy rotation

Missing Results

Check if you're filtering too aggressively
Use -mc all to see all responses
Disable auto-calibration temporarily
Use verbose mode -v to see what's happening

Resources

Official GitHub: https://github.com/ffuf/ffuf
Wiki: https://github.com/ffuf/ffuf/wiki
Codingo's Guide: https://codingo.io/tools/ffuf/bounty/2020/09/17/everything-you-need-to-know-about-ffuf.html
Practice Lab: http://ffuf.me
SecLists Wordlists: https://github.com/danielmiessler/SecLists

Quick Reference Card

Task Command Template

Directory Discovery ffuf -w wordlist.txt -u https://target.com/FUZZ -ac

Subdomain Discovery ffuf -w subdomains.txt -u https://FUZZ.target.com -ac

Parameter Fuzzing ffuf -w params.txt -u https://target.com/page?FUZZ=value -ac

POST Data Fuzzing ffuf -w wordlist.txt -X POST -d "param=FUZZ" -u https://target.com/endpoint

With Extensions Add -e .php,.html,.txt

Filter Status Add -fc 404,403

Filter Size Add -fs 1234

Rate Limit Add -rate 2

Save Output Add -o results.json

Verbose Add -c -v

Recursion Add -recursion -recursion-depth 2

Through Proxy Add -x http://127.0.0.1:8080

Additional Resources

This skill includes supplementary materials in the resources/ directory:

Resource Files

WORDLISTS.md: Comprehensive guide to SecLists wordlists, recommended lists for different scenarios, file extensions, and quick reference patterns
REQUEST_TEMPLATES.md: Pre-built req.txt templates for common authentication scenarios (JWT, OAuth, session cookies, API keys, etc.) with usage examples

Helper Script

ffuf_helper.py: Python script to assist with:
Analyzing ffuf JSON results for anomalies and interesting findings
Creating req.txt template files from command-line arguments
Generating number-based wordlists for IDOR testing

Helper Script Usage:

Analyze results to find interesting anomalies

python3 ffuf_helper.py analyze results.json

Create authenticated request template

python3 ffuf_helper.py create-req -o req.txt -m POST -u "https://api.target.com/users"
-H "Authorization: Bearer TOKEN" -d '{"action":"FUZZ"}'

Generate IDOR testing wordlist

python3 ffuf_helper.py wordlist -o ids.txt -t numbers -s 1 -e 10000

When to use resources:

Users need wordlist recommendations → Reference WORDLISTS.md
Users need help with authenticated requests → Reference REQUEST_TEMPLATES.md
Users want to analyze results → Use ffuf_helper.py analyze
Users need to generate req.txt → Use ffuf_helper.py create-req
Users need number ranges for IDOR → Use ffuf_helper.py wordlist

Notes for Claude

When helping users with ffuf:

ALWAYS include -ac in every command - This is mandatory for productive pentesting and result analysis
When users mention authenticated fuzzing or provide auth tokens/cookies:
Suggest creating a req.txt file with the full HTTP request
Show them how to insert FUZZ where they want to fuzz
Use ffuf --request req.txt -w wordlist.txt -ac
Always recommend starting with -ac for auto-calibration
Suggest appropriate wordlists from SecLists based on the task
Remind users to use rate limiting (-rate ) for production targets
Encourage saving output to files for documentation: -o results.json
Suggest filtering strategies based on initial reconnaissance
Always use the FUZZ keyword (case-sensitive)
Consider stealth: lower threads, rate limiting, and delays for sensitive targets
For pentesting reports, use -of html or -of csv for client-friendly formats
When analyzing ffuf results for users:
Assume they used -ac (if not, results will be too noisy)
Focus on anomalies: different status codes, response sizes, timing
Look for interesting endpoints: admin, api, backup, config, .git, etc.
Flag potential vulnerabilities: error messages, stack traces, version info
Suggest follow-up fuzzing on interesting findings