Password mask attacks explained: What are they & how do they work?

Credential-based attacks remain one of the most effective techniques used by cybercriminals to breach enterprise networks. In 2024 alone, 88% of web application attacks involved the use of stolen credentials, according to Verizon’s 2025 Data Breach Investigations Report. Among these techniques, mask attacks remain popular due to their efficiency in cracking password hashes using common patterns and user behavior.

In this article, we’ll explain how mask attacks work, how attackers use compromised hashes from breaches to execute them, and what organizations can do to strengthen their defenses against password-based threats.

What is password cracking?

At its core, password cracking is the process of trying to guess the original password that produced a given hash. It’s important to understand that hashes cannot be reversed — a hashing algorithm is a one-way operation. When you log into an application that uses password hashing, the system doesn’t store your actual password. Instead, it stores a hash generated by an algorithm like Argon2, bcrypt, or MD5, often combined with a salt to make attacks more difficult.

If you’ve participated in red team exercises or conducted Active Directory audits, you’ve likely encountered password dumps — for example, from LSASS or NTDS.DIT/SYSTEM files. These dumps contain hashed credentials that attackers or security professionals may attempt to crack. In Windows environments, these are typically NTLM hashes, while in Linux/Unix systems, you’re more likely to see hashes like SHA-512.

Cracking these hashes can serve multiple purposes: to evaluate how well users are following secure password practices, or in an attack context, to gain access and pivot to other systems or accounts within the network.

What is a password mask attack?

Mask attacks are a targeted brute-force technique used by bad actors to crack passwords. Traditional brute-force attacks systematically try every possible combination of letters, numbers, and symbols to guess a target password. With mask attacks, the goal is to reduce the quantity of password guesses to an approachable chunk of the total possibilities.

Attackers use information about password creation habits, like common composition patterns, to craft these password attacks.

How mask attacks improve brute-force password cracking efficiency

Attackers use several techniques for cracking password hashes, but brute-forcing every possible combination quickly becomes impractical due to the sheer size of the search space, especially as password length increases. Mask attacks offer a more efficient alternative by narrowing the scope of guesses to specific character patterns based on common password structures.

Instead of testing all possibilities, a mask attack focuses on likely formats: for example, an 8-character password that follows a pattern like Uppercase-Lowercase-Lowercase-Digit-Digit-Digit-SpecialCharacter. By targeting these known patterns, attackers significantly reduce the number of guesses needed to find valid matches. Typically, they begin with shorter, simpler patterns and gradually work toward more complex ones, since the time to crack increases exponentially with each added character.

Importantly, attackers don’t need to crack every password in a compromised dataset. Gaining access to just a handful of valid credentials — especially those tied to domain users — can provide a foothold to begin enumeration, lateral movement, and privilege escalation within the environment. These tactics align closely with techniques documented in the MITRE ATT&CK framework, which outlines common adversary behaviors used during credential access and post-exploitation.

Tips for preventing password mask attacks

While mask attacks rely on educated guessing, organizations can significantly reduce their effectiveness by improving password hygiene and implementing layered defenses. Here are a few practical ways to mitigate the risk:

1. Enforce strong password policies

Avoid passwords that follow predictable patterns. Instead:

• Require longer passwords (e.g. 20+ characters) — these take significantly more time and resources to crack
• Encourage the use of passphrases — a type of password made up of three or four random, unrelated words strung together
• Avoid enforcing composition rules that lead to predictable formats

2. Implement a banned password list

Use a banned-password list that prevents users from selecting common or compromised passwords, including those that match known patterns exploited in mask attacks.

3. Implement multi-factor authentication (MFA)

Multi-factor authentication requires users to verify their identity through a secondary method, such as a mobile app or a text message code. This adds an additional layer of security that significantly limits the impact of a compromised password, even if it’s cracked via a mask attack.

4. Salt and hash passwords securely

Always store passwords using modern hashing algorithms like bcrypt or Argon2, with a unique salt per user. This prevents attackers from using precomputed hash tables or applying the same attack across multiple accounts.

5. Educate users about password best practices

Security awareness training should include guidance on:

• Avoiding reused passwords
• Not following easy-to-guess formats (e.g. Name123!)
• Using password managers to generate and store secure passwords

Secure your Active Directory against mask attacks

Mask attacks demonstrate what a relatively unskilled attacker can do with a public breach if passwords aren’t sufficiently strong, and users are reusing passwords. By simply using longer and stronger password policies driven by Specops Password Policy, preferably combined with a breached password solution such as the optional Specops Breached Password Protection feature, organizations can significantly reduce their exposure to targeted password attacks.

The Breached Password Protection solution is updated daily, and includes over 4 billion compromised passwords, including the HaveIbeenPwned list, the latest Collection lists, as well as thousands of other known leaked lists as recommended by regulatory bodies like NIST. With this solution in place, you can remove a lot of low-hanging fruit that could lead to initial access from a bad actor.

Interested to find out how Specops Password Policy could strengthen your organization’s security? Request a free live demo today.

Frequently Asked Questions