What is a Brute Force Attack?

Types of Brute Force Attack

Brute force attacks come in various forms, each targeting different aspects of a system’s security. Here are some common types:

Simple Brute Force Attack

This is the basic form of brute force attack where the attacker tries all possible combinations of characters until the correct one is found. For example, in a password brute force attack, the attacker systematically tries every possible password until the correct one is discovered.

Dictionary Attack

In this type of attack, instead of trying all possible combinations of characters, the attacker uses a predefined list (dictionary) of commonly used passwords or phrases. This list may include words from dictionaries, commonly used passwords, or previously breached passwords. Dictionary attacks are often more efficient than simple brute force attacks because they prioritize trying likely passwords first.

Hybrid Brute Force Attack

A hybrid brute force attack combines elements of dictionary attacks with traditional brute force techniques. The attacker may append or prepend numbers, symbols, or common variations to dictionary words to create new potential passwords. This approach is particularly effective against passwords that consist of dictionary words with minor modifications.

Rainbow Table Attack

Rainbow table attacks leverage precomputed tables (rainbow tables) containing the hashes of commonly used passwords and their corresponding plaintext values. Instead of hashing each attempted password individually, the attacker can compare the hash of the target password directly with entries in the rainbow table to find a match quickly. This significantly speeds up the process of password cracking, especially for systems that use weak hashing algorithms or have insufficiently long and complex passwords.

Credential Stuffing

While not strictly a brute force attack, credential stuffing involves using previously compromised username/password pairs to gain unauthorized access to other accounts. Attackers automate the process of trying these credentials across various services or platforms in the hope that users reuse passwords across multiple accounts. This method is effective because many users use the same credentials across multiple services, allowing attackers to gain access to additional accounts with minimal effort.

Each of these brute force attack types exploits different weaknesses in system security and authentication mechanisms, highlighting the importance of implementing strong password policies, multi-factor authentication, and robust security measures to defend against such threats.

The Motives Behind Brute Force Attacks

A brute force attack is usually the first point of entry for an attacker when they are looking for vulnerabilities to exploit. Due to the scattergun nature of the attack, they are likely canvassing a large number of organizations at the same time and letting the automated attacks carry out hoping to eventually get a match. Once they gain access, attackers can continue to use brute force to escalate their privileges and move laterally through the network.

Another common motive of brute force attacks is to look for hidden web pages within a website. These are live pages that are not linked from anywhere on the site. Attackers essentially use brute force attacks to guess the URLs of such pages and then attempt to exploit any security vulnerabilities they might find on half-finished ones.

How Does a Brute Force Attack Work?

A brute force attack systematically tries all possible combinations of characters until the correct password or encryption key is found. The process involves several steps:

1. Generating Combinations: The attacker first determines the character set and length of the password or encryption key to be cracked. This could include lowercase letters, uppercase letters, numbers, and special characters. Based on the defined character set and length, the attacker generates a list of all possible combinations.
2. Testing Combinations: Using automated software or scripts, the attacker begins testing each combination one by one. The software sends each combination as a login attempt or decryption attempt, depending on the target system’s nature (e.g., a login page, an encrypted file, etc.).
3. Feedback Mechanism: The attacker analyzes the response from the system after each attempt. If the attempted combination is incorrect, the system typically denies access or fails to decrypt the data. However, if the combination is correct, the system grants access or successfully decrypts the data.
4. Iterative Process: The attack continues iteratively, trying each combination until the correct one is discovered. Depending on the complexity of the password or encryption key and the computational power available to the attacker, this process could take seconds, hours, days, or even longer.
5. Optimization Techniques: To enhance efficiency, attackers may employ various optimization techniques such as parallelization, where multiple combinations are tested simultaneously using distributed computing resources or specialized hardware like GPUs. They may also prioritize certain combinations based on known patterns (e.g., dictionary words, common character substitutions) to increase the likelihood of success early in the attack.
6. Completion and Access: Once the correct password or encryption key is found, the attacker gains unauthorized access to the system or decrypts the protected data. This access can be exploited for various malicious purposes, including theft of sensitive information, unauthorized financial transactions, or further compromising the system’s security.

Brute force attacks rely on the attacker’s computational resources and the time it takes to exhaustively search through all possible combinations. Defending against brute force attacks typically involves implementing measures such as account lockouts after multiple failed login attempts, using strong and complex passwords, implementing multi-factor authentication, and employing intrusion detection systems to detect and mitigate suspicious login attempts.

Tools Used for Brute Force Attacks

Attackers have access to a variety of tools and software designed specifically for conducting brute-force attacks. These tools automate the process of generating and testing password combinations, making it easier for attackers to carry out such attacks efficiently. Some commonly used tools for brute force attacks include:

John the Ripper

This is one of the most popular and widely used password-cracking tools. John the Ripper supports various password hash types and can perform dictionary attacks, brute force attacks, and hybrid attacks. It is highly customizable and can run on multiple platforms, including Unix, Windows, and macOS.

Hashcat

Hashcat is a powerful open-source password recovery tool that supports a wide range of hashing algorithms and attack modes, including brute force, dictionary attacks, and hybrid attacks. It is known for its speed and efficiency, especially when running on GPUs (Graphics Processing Units), making it a popular choice for cracking complex passwords.

Hydra

Hydra is a versatile and fast network login cracker that supports various protocols, including HTTP, HTTPS, FTP, SSH, Telnet, and more. It can perform brute force attacks, dictionary attacks, and password guessing attacks against login interfaces, making it suitable for targeting a wide range of services and applications.

Medusa

Similar to Hydra, Medusa is a command-line password cracking tool that supports multiple protocols and services, including SSH, FTP, Telnet, HTTP, and more. It can perform brute force attacks and dictionary attacks against login interfaces and supports parallelized attacks for increased speed.

Crowbar

Crowbar is a brute force attack tool specifically designed for cracking remote authentication services, such as SSH, RDP, VNC, and others. It supports various authentication methods, including password-based, key-based, and keyboard-interactive authentication, and can perform both dictionary attacks and brute force attacks.

Aircrack-ng

Aircrack-ng is a popular suite of tools for auditing wireless networks. It includes tools for capturing packets, performing cryptographic attacks, and cracking WEP and WPA/WPA2-PSK keys. Aircrack-ng can perform brute force attacks against captured handshakes to recover Wi-Fi passwords.

How to Defend Against Brute Force Attacks

There is something in your favor when it comes to brute force attacks – time! Brute force attacks are not instant, so you have some time to spot one in action and take the correct steps to prevent it from going any further. If you can increase the amount of time it takes for an attacker to force your way into your systems, then you put yourself in a good position. Here are a few things you can do:

• Captcha: A defense against automated attacks, Captcha adds another layer of security by requiring you to essentially prove that you are human by completing a task (usually a sum or picture identification)
• Multi-factor authentication: MFA goes further than Captcha by essentially requiring the person who created the account is the logging in. Most forms of MFA include answering a personal question, but some go as far as identification through biometrics.
• Using better passwords: Ensure that your users create passwords that are complex, long and are not made up of known words. If you can make your passwords a random combination of letters, numbers and special characters (at least 10 characters in length), you make it significantly harder to crack your password through brute force.

Monitor attempted logins: If you are continuously monitoring login attempts you should be able to easily spot when there has been an unusually large number of failed logons over a small period of time. You can then take steps to disable the user account in question whilst you investigate.