What Is a Brute-Force Attack?
A brute-force attack is a tactic used by threat actors to gain unauthorized access to an account, system, or encrypted data by systematically trying every possible password, encryption key, or credential combination until the correct one is found. These attacks rely on trial-and-error and can be automated with software that rapidly tests millions of possibilities.
While simple, brute-force attacks can be effective against weak or reused passwords. Threat actors often turn to this attack after they gain credentials (emails, usernames, or passwords) from the dark web or a previous attack and need to determine what access these credentials allow.
Types of Brute-Force Attacks
A brute-force attack can take many forms, including:
1. Knowledge-Based Attack
A knowledge-based attack leverages information gathered about a user from online sources or through social engineering, allowing an attacker to combine the user’s data to guess their password.
2. Dictionary Attack
A dictionary attack relies on commonly used words and phrases to guess a user’s password.
3. Credential Stuffing
Credential stuffing takes advantage of the fact that users often recycle passwords by using stolen passwords from one site to try to gain access to another.
4. Reverse Brute-Force Attack
Instead of guessing passwords for a given username, a reverse brute-force attack starts with a common password, like “12345” or “password,” and attempts to guess the username
5. Hybrid Attack
A hybrid attack utilizes multiple brute-force methods in one attack, such as combining knowledge about the intended target and dictionary words and phrases, attackers attempt to guess user passwords. For example, if the threat actor knows the user’s birthday and partner’s name, they may combine that information to guess their password.
6. Password Spraying
A password spraying account tries a small number of common passwords (e.g., “Welcome123”, “Password1”) across many accounts, instead of many passwords against one account. This technique avoids account lockouts and can be effective at scale against large user bases.
7. Offline Brute-Force Attack (Hash Cracking)
Offline brute-force (hash cracking) occurs when a threat actor obtains password hashes (e.g., from a previous breach) and runs guesses locally against those hashes using powerful GPUs or cracking tools.
How A Brute-Force Attack Works
As shown above, there are multiple methods a threat actor can utilize during a brute-force attack. However, no matter the specifics, each attack follows the same pattern of behavior and contains the same end goal of obtaining malicious access.
The steps to a brute-force attack are:
- Choose a Target: The threat actor selects the organization, account(s), or system they want to gain access to.
- Gather Information and Context: The threat actor conducts basic research about the user or utilizes the dark web to try to obtain information, credentials, or other data that will help them gain access faster.
- Pick An Attack Method: Based on the intel gathered, the threat actor will pick a method (or multiple methods) from the list above to use as the main attack tactic.
- Automate Attempts: Brute-force attacks often rely on bots, malware, or other automated methods to conduct the attack. This allows the threat actor to try a high volume of guesses in a short amount of time.
While not an official step in the process, if a brute-force attack is successful, it’s not uncommon for a threat actor, especially initial access brokers, to then sell that access to other cybercriminals or exploit it to launch a secondary, sophisticated attack.
Why Are Brute-Force Attacks Effective?
There are many reasons why threat actors turn to brute-force attacks, the most obvious of which is that, well, users are bad at securing their credentials and utilizing complex, hacker-resistant passwords. For threat actors, brute-force attacks are often a low-tech, highly successful method to gain access.
Other reasons brute-force attacks are effective include:
- Weak passwords (e.g. use common phrases, are short, or don’t utilize a combination of letters, numbers, and symbols) are commonplace
- Users often reuse parts of, or entire passwords across accounts
- Humans tend to make predictable choices with passwords (e.g. adding 123 to the end)
- A lack of multi-factor authentication (MFA) across organizations’ environments allows threat actors to be granted access with just a single set of credentials
- Insufficient rate limiting, lockouts, or other access control methods on accounts allows threat actors to keep guessing passwords
- Absent logging or monitoring of accounts, credentials, and user behavior allows threat actors to attempt to login to accounts and make lateral movement post-access
- Offline cracking of hashes can occur without detection
- Development of botnets makes brute-force attacks possible at scale
How To Defend Against Brute-Force Attacks
There are a myriad of ways organizations and individuals can protect accounts against brute-force attacks, and a layered approach is by far the best to ensure security at multiple levels.
1. Enforce the Use of Lengthy and Complex Passwords.
The longer and more complex a password is, the more time and computing power it takes threat actors to guess it. Consider requiring passwords of 8 to 12 characters for all users. The use of upper- and lower-case letters and special characters can add additional complexity and challenges for an attacker to overcome.
2. Deploy Multi-Factor Authentication (MFA) for All Users.
If an attacker guesses a user’s login credentials, MFA can act as a backstop. The threat actor is still thwarted if the account requires that the user inputs additional information, such as a one-time password sent to their phone or email, in order to be granted access. The key factor involved with MFA is the addition of that extra layer of identification, which stops a brute-force attack before damage is done.
3. Set Account Lockout and Rate-Limiting Rules.
Brute-force attacks, especially those reliant on bots, need a high number of attempts to guess an account’s credentials. By setting lockout and rate-limiting rules, the threat actor will be unable to continually try to gain access. An additional security measure is to have alerting in place if that rate limit is reached, so security teams are informed that something may be amiss.
4. Require CAPTCHA.
Brute-force attacks often involve bots. Requiring a CAPTCHA — a challenge–response protocol to verify that a visitor to a site is human — can stop attacks. Regardless of the method of CAPTCHA deployed, adding this layer can prevent bots from running a script, forcing the human threat actor to intervene.
5. Apply IP Blacklisting and Geofencing.
This security method blocks access from certain regions or high-risk networks, preventing foreign threat actors from attempting to gain access to accounts.
6. Monitor and Alert on Login Anomalies.
Deploying detection and response software that can detect suspicious account patterns (e.g. repeated failed logins) can help organizations respond to brute-force attacks before they find success and escalate.
7. Employ a Zero Trust Strategy and Enforce Principle of Least Privilege (PoLP).
These two access control strategies require that a user be verified (zero trust), and that access is limited to what is required to complete a task or job, and nothing more (PoLP). Both of these controls limit threat actors’ abilities to gain access and/or then utilize that access to escalate attacks.
Explore identity and access management (IAM) best practices, including zero trust strategies and PoLP implementation.
8. Educate Users with Security Awareness Training.
Reducing human risk reduces the chance of a successful brute-force attack. With comprehensive training that helps users spot the signs of brute-force attacks, harden their passwords and credentials, and stop behaviors that may give threat actors an upperhand (e.g reusing passwords), organizations can reduce their overall human risk.
Learn how to solve common security awareness training challenges to reduce your organization’s human risk.
9. Utilize Endpoint Security.
Many brute-force attacks start on the endpoint, or accounts connected to an endpoint, so endpoint security offers a number of advantages in stopping these attacks. Comprehensive endpoint security should: detect repeated login attempts, apply account lockout controls, monitor for credential theft malware, stop unauthorized access tools from installation, support MFA enforcement, and provide real-time alerting and response.
Better understand how to defend against identity-related threats with the 2025 Arctic Wolf Security Operations Report.
Explore credential theft tactics, and how to defend against them.
