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

bash

# 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

1. Directory and File Discovery

bash

# 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

2. Subdomain Enumeration

bash

# 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)

3. Parameter Fuzzing

bash

# 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

4. POST Data Fuzzing

bash

# 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

5. Header Fuzzing

bash

# 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.

bash

# 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

bash

# 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

bash

# 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

bash

# 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

bash

# From a file containing raw HTTP request
ffuf --request req.txt -w /path/to/wordlist.txt -ac

Example req.txt file:

http

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

bash

# 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

bash

# 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

bash

# 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

bash

# 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

bash

# 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

bash

# 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

1. ALWAYS Use Auto-Calibration

Use

-ac

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

bash

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

2. Use Raw Requests for Authentication

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

--request

bash

# 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

3. 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

3. Rate Limiting for Stealth

Use

-rate

to avoid triggering WAF/IDS or overwhelming the server:

bash

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

4. 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
```

5. Save Results Appropriately

Always save results to a file for later analysis:

bash

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

6. 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

7. Recursion Depth

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

bash

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

Common Patterns and One-Liners

Quick Directory Scan

bash

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

Comprehensive Scan with Extensions

bash

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)

bash

# 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

bash

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

bash

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

POST Login Brute Force

bash

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

bash

# 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:

bash

# 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

ffuf-web-fuzzing

NPX Install

SKILL.md Content

FFUF (Fuzz Faster U Fool) Skill

Overview

Installation

Core Concepts

The FUZZ Keyword

Multi-wordlist Modes

Common Use Cases

1. Directory and File Discovery

2. Subdomain Enumeration

3. Parameter Fuzzing

4. POST Data Fuzzing

5. Header Fuzzing

Filtering and Matching

Matchers (Include Results)

Filters (Exclude Results)

Auto-Calibration (USE BY DEFAULT!)

Rate Limiting and Timing

Rate Control

Time Limits

Output Options

Output Formats

Advanced Techniques

Using Raw HTTP Requests (Critical for Authenticated Fuzzing)

Proxy Usage

Cookie and Authentication

Encoding

Testing for Vulnerabilities

Batch Processing Multiple Targets

Best Practices

1. ALWAYS Use Auto-Calibration

2. Use Raw Requests for Authentication

3. Use Appropriate Wordlists

3. Rate Limiting for Stealth

4. Filter Strategically

5. Save Results Appropriately

6. Use Interactive Mode

7. Recursion Depth

Common Patterns and One-Liners

Quick Directory Scan

Comprehensive Scan with Extensions

Authenticated Fuzzing (Raw Request)

API Endpoint Discovery

Subdomain Discovery with Auto-Calibration

POST Login Brute Force

IDOR Testing with Auth

Configuration File

Troubleshooting

Too Many False Positives

Too Slow

Getting Blocked

Missing Results

Resources

Quick Reference Card

Additional Resources

Resource Files

Helper Script

Notes for Claude