Brute force attacks: Understanding, types, and prevention

A brute force attack is a method malicious actors use to guess at digital credentials, like usernames and passwords, to access a private system.

What is a brute force attack?

During a brute force attack, bad actors make unauthorized attempts to access systems, accounts, or data by systematically trying every conceivable combination of usernames and passwords until they find the correct one. Unlike more sophisticated attacks that exploit code or social engineering vulnerabilities, brute force attacks rely on persistence and computing power to crack authentication credentials.

To enact a brute force attack, hackers use automated tools that quickly submit thousands or even millions of login attempts until they successfully guess the right combination. 

According to the 2024 IBM Cost of a Data Breach Report, compromised credentials were the most common attack vector, responsible for nearly 16% of breaches with an average cost of $4.81 million per breach.

How brute force attacks work

Brute force attacks leverage raw computing power and automation to overcome authentication systems.

How brute force attacks typically work:

1. Target identification: Attackers target a login page, authentication API, or encryption system.
2. Information gathering: They collect any available information about username structures, password policies, or previously leaked credentials associated with the target.
3. Automated attempts: Attackers generate and test numerous credential combinations using specialized tools, submitting them automatically to the target system.
4. Account compromise and exploitation: Once attackers discover valid credentials, they gain the same level of access as the compromised account, potentially leading to data breaches, lateral movement through the network, or the establishment of persistent access.

No username/password combination is entirely hack-proof. With enough time and computing resources, attackers can eventually crack any combination through brute force. However, the more complex the credentials, the more time and resources are required, which is why strong password policies and additional, more modern security measures are essential.

Types of brute force attacks

Simple brute force attack

In a simple brute force attack, bad actors use automated tools to systematically try various character combinations based on information they might know about the target or using common password patterns. This approach relies more on human intuition and logical deduction than automated tools, making it less scalable but sometimes effective against accounts with weak or predictable passwords.

Dictionary attack

A dictionary attack is a refined form of brute force that uses a predefined list of words, phrases, and common passwords instead of trying random character combinations. Dictionary attacks test likely passwords first, significantly reducing the time to crack common credentials.

“Dictionaries” often include:

• Common passwords (like “password123” or “admin”)
• Words from actual dictionaries
• Names, dates, and common phrases
• Previously leaked passwords from data breaches

Reverse brute force attack

In a reverse brute force attack, attackers start with a known password (often obtained from data breaches) and attempt to find the username it belongs to. This method is particularly effective when attackers can access common passwords and want to see which accounts in a system use them.

Credential stuffing

Credential stuffing leverages username and password combinations leaked from previous data breaches. Attackers assume that many people reuse the same credentials across multiple sites, so they test known username/password pairs against various services. 

Hybrid brute force attack

Hybrid attacks combine elements of dictionary attacks with brute force techniques. These attack methods start with dictionary words and apply various transformations and character substitutions (like replacing 'a' with '@' or adding numbers at the end). This approach balances efficiency with thoroughness, making it particularly dangerous.

Password spraying

Unlike traditional brute force attacks that try many passwords against one account, password spraying attempts a few commonly used passwords against many accounts. This method helps attackers avoid account lockouts by limiting attempts per account while maximizing the chance of finding at least one vulnerable credential in a system.

The impact of brute force attacks

Brute force attacks can have far-reaching consequences across an organization.

10 ways to prevent brute force attacks

Protecting systems against brute force attacks requires a multi-layered security approach.

Brute force prevention strategies:

1. Implement strong password policies

Mandate complex passwords that are difficult to guess.

Effective password security includes:

• Minimum length of 12–16 characters
• A combination of upper and lowercase letters, numbers, and special characters
• No common words or predictable patterns

The National Institute of Standards and Technology (NIST) password guidelines continue to evolve, recommending longer passwords, improved usability and passwordless solutions.

2. Deploy multifactor authentication (MFA) and adaptive multifactor authentication (AMFA)

MFA is one of the more effective defenses against brute force attacks, requiring users to provide two or more verification factors:

• Something they know (password)
• Something they have (smartphone or security key)
• Something they are (fingerprints, facial recognition)

 Adaptive MFA (AMFA) enhances this protection by intelligently adjusting authentication requirements based on risk factors like device, location, and behavior patterns.

3. Implement account lockout policies

Limit the number of failed login attempts before temporarily locking an account to prevent attackers from making unlimited guesses.

Best practices include:

• Locking accounts after 3–5 failed attempts
• Implementing progressive delays between login attempts
• Offering secure account recovery options
   

4. Use CAPTCHA systems

CAPTCHA challenges help distinguish between human users and automated bots. Implementing CAPTCHA after failed login attempts can significantly reduce the effectiveness of automated brute force tools while minimizing disruption to legitimate users.

5. Implement IP blocking and rate limiting

Monitor and restrict suspicious access patterns:

• Block IP addresses that show brute attack patterns
• Limit the number of requests from a single IP address
• Implement geographical restrictions where appropriate
• Set rate limits on authentication endpoints
   

6. Employ secure password storage

Never store passwords in plaintext. Instead:

• Use strong, modern hashing algorithms (like bcrypt, Argon2, or PBKDF2)
• Implement salting to prevent rainbow table attacks
• Regularly update hashing methods as more robust standards emerge
   

7. Deploy threat intelligence and real-time brute force detection

Employ continuous monitoring to detect and respond to brute force attempts:

• Use security information and event management (SIEM) solutions
• Deploy intrusion detection systems specifically configured to identify brute force patterns
• Establish baseline authentication behavior and alert on deviations
• Leverage threat intelligence feeds to block known malicious IP addresses
   

8. Apply the principle of least privilege

Limit the damage from compromised accounts by ensuring users have only the minimum access privileges needed to perform their job functions. Regularly review and audit access permissions, especially for administrative accounts.
 

9. Consider passwordless authentication

Move beyond traditional passwords to more secure authentication methods:

• Biometric authentication
• Hardware security keys
• Certificate-based authentication
• Single sign-on (SSO) that integrates with strong, passwordless authentication methods 

10. Regular security training and awareness

Educate employees about:

• Creating and managing strong passwords
• Recognizing phishing attempts that try to steal credentials
• The importance of not reusing passwords across services
• How to report suspected security incidents

Recent trends in brute force attacks

Brute force attacks continue to evolve as cybersecurity defenses improve:

• AI-powered brute force attacks: Machine learning (ML) algorithms help attackers generate more intelligent password guesses based on patterns from previous breaches, user behavior analysis, and predictive modeling of password creation tendencies. 
• Brute force attacks against IoT devices: Internet of Things (IoT) devices often have weak default credentials and become prime targets.
• Cloud service attacks: Attackers increasingly target cloud service credentials as more businesses migrate to the cloud.
• API-focused attacks: Authentication APIs are becoming common targets as more applications rely on them.
• Supply chain attacks: Malicious actors target weaker security in vendor systems to access larger organizations.

Enterprise brute force protection strategies

Organizations with complex infrastructure require comprehensive protection approaches:

• Centralize authentication logging across all systems for unified monitoring
• Implement Identity governance to automatically detect and remediate excessive permissions
• Deploy Zero Trust architecture requiring continuous verification
• Establish security operation centers (SOCs) with dedicated brute force monitoring
• Conduct regular penetration testing, specifically targeting authentication systems

Brute force attack detection signs

Security teams should watch for indicators of potential brute force attempts, including:

• Unusual spike in failed login attempts
• Login attempts occurring at unusual times
• Authentication attempts from unusual geographic locations
• Multiple login attempts across different user accounts from the same IP address
• Sequential username attempts following predictable patterns
• Abnormal traffic volumes to authentication endpoints

Brute force attack FAQs

Q: What’s the difference between a brute force attack and a dictionary attack?

A: In a brute force attack, bad actors methodically try every possible combination of characters. In dictionary attacks predefined lists of likely passwords are used, making it more efficient but potentially less comprehensive.

Q: How quickly can a brute force attack crack a password?

A: The time required depends on several factors:

• Password length and complexity
• Computing power available to the attacker
• Efficiency of the cracking algorithm
• Whether the password appears in standard dictionaries

Q: Are cloud services vulnerable to brute force attacks?

A: The public accessibility of cloud services makes them visible to attackers. The high value of the data they protect makes them attractive targets. To address this, cloud providers commonly implement additional security measures like automatic lockouts, MFA, and anomaly detection to address this.

Stay ahead of brute force attacks

Get rock-solid protection from brute force attacks and other Identity-based threats with Okta.

Learn more