Table of contents
- What is a brute force attack
- How a brute force attack works
- How to prevent a brute force attack
- How to react after a brute force attack
In the increasingly complex world of cyber security, one of the most common yet underestimated threats is the brute force attack. This technique is used by cybercriminals to gain unauthorized access to digital systems by systematically trying every possible combination of credentials until they find the right one.
In this article, we will take an in-depth look at what a brute force attack is, how it works, what risks it poses, and most importantly, how to prevent it and deal with its consequences.
What is a brute force attack
A brute force attack is a hacking technique that aims to crack a login system by trying every possible combination of usernames and passwords until the correct credentials are found.
It is one of the simplest and most direct attack methods but can be extremely effective if no proper security measures are in place.
The term itself refers to the “brute” nature of the approach: no subtlety, no social engineering, just pure computing power trying millions of combinations in rapid succession. Cyber attackers often automate this process using specific tools such as Hydra, John the Ripper, Aircrack-ng, or Hashcat, capable of testing thousands of password combinations per second.
The most common targets of brute force attacks include email accounts, website administration panels, FTP servers, databases, banking platforms, and social media logins.
How a brute force attack works
A brute force attack always follows the same core logic: attempting countless combinations of credentials until the correct one is found.
However, the methodology and tools used can vary depending on the attacker’s goal, resources, and the target system’s security level. Let’s explore the main types of brute force attacks and how they are carried out.
Direct online attack
The online brute force attack is the most basic and noisy form of this technique. The attacker uses automated software to continuously send login requests to a website, an FTP service, an admin panel, or any system requiring authentication.
Each request contains a different username and password combination, usually sourced from lists of common credentials or generated in real-time.
This type of attack is easily detectable because it results in hundreds or thousands of failed login attempts in a short period, creating abnormal traffic patterns and filling the access logs.
Esempio
A hacker targets the login page of a WordPress website. They use a script with the Hydra tool to automatically test thousands of password combinations against wp-login.php, trying popular passwords like “123456”, “password”, “qwerty”, or “admin2024”. If the website lacks protections like login attempt limits, the attack has a high chance of success.
Offline attack
The offline brute force attack is more sophisticated and stealthy. In this scenario, the attacker does not attempt to log in directly to the target system. Instead, they acquire a database of password hashes—possibly obtained from a previous data breach—and attempt to crack them locally, without being constrained by rate limits or detection systems.
Using tools like John the Ripper or Hashcat, the attacker can launch large-scale computational attacks on their own hardware or via cloud infrastructures, testing millions of password combinations per second, especially with modern GPU support.
Example
A cybercriminal manages to access a Linux server’s shadow file, which contains encrypted (hashed) user passwords. They use Hashcat to compare these hashes against a massive password dictionary containing over 1 million entries, looking for a match.
Dictionary attack
A variant of the brute force attack is the dictionary attack. Here, instead of trying every possible combination, the attacker tests a list of known or commonly used passwords, statistically increasing their chances of success.
These dictionaries are often built from passwords leaked in previous data breaches, or they contain predictable choices like “welcome”, “password123”, “admin2024”, birthdays, or pet names.
Example
A hacker, wanting to attack a corporate email account, prepares a dictionary of passwords that include the name of the company followed by numbers (e.g. “Company2024!”, “Company123”), combining them with common words such as “work”, “office”, “login”.
Combinatorial attack
The combinatorial attack is an evolution of the dictionary attack. Instead of testing only predefined words, the attacker combines two or more words from the dictionary, adding numbers or special characters, reducing the time needed to crack the password while increasing the chances of success.
Example
Suppose the attacker knows that the target user often uses personal information in their passwords, such as their pet’s name or year of birth. They will build a dictionary with keywords like “Charlie”, “1990”, “Rome” and generate combinations like “Charlie1990!”, “RomeCharlie!”, or “1990Rome@”.
Code snippet demonstration
To better understand the logic behind a brute force online attack, here’s a simple demonstration in Python (for educational purposes only):
import requests
url = "https://www.example.com/login"
username = "admin"
password_list = ["123456", "password", "admin123", "qwerty"]
for password in password_list:
data = {"username": username, "password": password}
response = requests.post(url, data=data)
if "Welcome" in response.text:
print(f"[+] Password found: {password}")
break
else:
print(f"[-] Failed attempt with password: {password}")This script automates the process of sending POST requests to a login form, trying different passwords from a predefined list. Obviously, using such a script without explicit authorization is a serious cyber crime.
Attack speed and limits
The speed and effectiveness of a brute force attack depend on several factors:
- Computational power
CPU, GPU, or server clusters. - Password complexity
Length, character variety, and unpredictability. - Maximum number of allowed attempts
Many systems block users after a few failed attempts. - Active defenses
Rate limiting, CAPTCHA, two-factor authentication.
To give a concrete idea, an 8-character password composed only of lowercase letters can be cracked in minutes using a common PC. A 12-character password containing symbols, numbers, and mixed case letters could require years to break, even with powerful hardware.
How to prevent a brute force attack
Protecting yourself from a brute force attack requires a mix of good security practices, smart configuration, and technological tools.
The first line of defense is to use strong and unique passwords. A good password should be long, include uppercase and lowercase letters, numbers, and special characters, and avoid using real words or obvious sequences.
Two-factor authentication (2FA) is another essential protection layer. It adds an extra verification step beyond the password, such as a one-time code or confirmation on a mobile device.
Limiting the number of login attempts is equally important. Temporarily blocking an account after several failed attempts makes a brute force attack much less effective. The use of CAPTCHA systems and anti-bot mechanisms also helps prevent automated login attempts.
Finally, it is crucial to constantly monitor login logs and set up intrusion detection systems (IDS) to detect suspicious activity in real time and take immediate action.
How to react after a brute force attack
If you suspect that you have been the target of a brute force attack, it is essential to act quickly to contain the damage and restore system security.
The first step is to analyze the access logs and identify any unusual login attempts from unfamiliar IP addresses or an excessive number of failed logins. Next, you should immediately reset all potentially compromised passwords, replacing them with new, strong credentials.
Blocking suspicious IP addresses through firewall rules or security software will help prevent further attacks. It’s also important to conduct a system integrity check to ensure no unauthorized changes have been made.
Lastly, you should inform any affected users if their accounts were compromised and review your security policies. Consider implementing additional protection measures such as multi-factor authentication, stricter password policies, and regular software updates.
Questions and answers
- What is a brute force attack?
A brute force attack is a hacking method where attackers try every possible combination of login credentials until they succeed. - What are the most common targets of brute force attacks?
Email accounts, website admin panels, FTP servers, databases, online banking platforms, and social media logins. - Can you detect a brute force attack?
Yes, these attacks often result in a large number of failed login attempts visible in system logs. - How can you prevent a brute force attack?
By using strong passwords, enabling two-factor authentication, limiting login attempts, and monitoring login logs. - Can any system be compromised by brute force?
Any system without adequate protection can be vulnerable, especially if weak passwords are used. - How long does a brute force attack take?
It depends on password complexity and computing power. It can range from seconds to years. - What happens if a brute force attack succeeds?
The attacker gains unauthorized access, potentially leading to data theft, financial loss, or privacy breaches. - Is a long password enough to stop brute force attacks?
A long password helps, but it should also be complex and supported by additional security measures. - What’s the difference between a brute force attack and phishing?
Phishing tricks users into revealing credentials, while brute force attacks try to guess them without user interaction. - What should you do after a brute force attack?
Analyze logs, reset passwords, block suspicious IPs, restore system integrity, and notify affected users.
