GPEN Password Attacks and Formats — Timed 10 Questions

Question 1

Refer to the exhibit. The penetration tester is unable to crack the hash using mode 1800. What is the most likely cause of this failure?

Accepted Answer

The hash mode 1800 is incorrect for a SHA-512 crypt implementation.. The exhibit shows a SHA-512 crypt hash (indicated by the $6$ prefix). Hashcat mode 1800 targets SHA-512 based hashes, but specifically for legacy systems or custom implementations. Modern Linux SHA-512 crypt hashes require mode 1800 to be configured correctly with the specific parameters. Misidentifying the hash format leads to incorrect salt parsing and improper algorithm selection, which are critical errors when attempting to recover secrets from standard Linux password storage files.

Answer

The salt is too short for the algorithm to process.

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The round count is too high for the hardware to process.

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The hash is actually a bcrypt hash which requires mode 3200.

Question 2

Which THREE factors significantly influence the time required to crack a password hash during an offline attack?

Accepted Answer

The length and complexity of the password.. The efficiency of an offline attack is governed by the speed of the hardware, the complexity of the hash function, and the quality of the dictionary or wordlist. Modern GPUs can perform billions of hashes per second, but complex algorithms like bcrypt or Argon2 are designed to be intentionally slow. Balancing these factors is essential for planning an engagement, as it determines whether cracking a specific hash is feasible within the allotted time frame of a test.

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The number of concurrent users on the network.

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The number of open ports on the target server.

Question 3

Refer to the exhibit. Which attack method is most likely to succeed given this password policy?

Accepted Answer

Password spraying across the organization.. The policy has a very strict account lockout of only 3 failed attempts. This effectively makes brute-forcing a single account online nearly impossible. However, the lack of a history check or other limitations might suggest other weaknesses. Spraying is the only viable online option, but the testing focus should shift towards offline cracking or non-password-based techniques, as standard online brute force will trigger an immediate and persistent lockout for the target user.

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Brute-force attack on a single account.

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Dictionary attack on a single account.

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Offline hash cracking of the SAM database.

Question 4

Which hashing algorithm is currently considered the most resistant to brute-force attacks due to its design as a memory-hard function?

Accepted Answer

Argon2. Argon2 is a memory-hard function, meaning it requires significant RAM to compute, in addition to CPU cycles. This design specifically targets the hardware advantage of GPUs and ASICs, which have many cores but limited high-speed memory per core. By forcing the computation to consume large amounts of memory, Argon2 makes it prohibitively expensive to parallelize the cracking process, offering superior protection compared to older algorithms like MD5 or SHA-1.

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MD5

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SHA-1

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DES

Question 5

Refer to the exhibit. What does this hash format indicate about the password for 'user1'?

Accepted Answer

The password is empty (null).. The exhibit shows a standard Windows SAM file format. The first part is the LM hash, and the second is the NTLM hash. The specific strings 'aad3b...' and '31d6c...' are the universal indicators for an empty or null password. In a penetration testing context, identifying these null hashes is a quick win, as it reveals accounts that have no password protection, allowing for immediate access without needing to run any cracking tools.

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The password is 'password'.

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The password has been recently changed.

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The account is locked and cannot be used.

Question 6

A penetration tester has extracted a set of password hashes from a compromised Linux system's `/etc/shadow` file. The hashes are in the format `$6$rounds=5000$salt$hash`. Which TWO of the following statements are true regarding the cracking of these hashes? (Choose two.)

Accepted Answer

The hashes use SHA-512 with 5000 rounds of key stretching, which slows down brute-force attacks.. The hashes use SHA-512 crypt with a specified number of rounds (5000) and a salt. Key stretching via multiple rounds increases the computational cost per guess, slowing down brute-force attacks. The rounds parameter is configurable and can be increased beyond the default to further hinder cracking. Salted hashes are not vulnerable to generic rainbow tables. Thus, the true statements are that the hashes use SHA-512 with 5000 rounds of key stretching, and that the number of rounds can be increased to further slow cracking.

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These hashes are unsalted, making them vulnerable to precomputed hash attacks.

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The hashes can be cracked using Hashcat mode 1800 without any additional parameters.

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The salt is fixed and known, so rainbow tables can be used to crack these hashes instantly.

Question 7

A penetration tester is preparing to crack a set of NTLM hashes obtained from a Windows domain controller. The hashes are unsalted and the passwords are suspected to be of moderate complexity. Which two techniques would be most effective for rapidly identifying weak passwords while minimizing computational resources? (Choose two.)

Accepted Answer

Dictionary attack with common password lists and mangling rules.. Rainbow tables and dictionary attacks with rules are both highly efficient for unsalted NTLM hashes. Rainbow tables trade storage for speed, allowing instant lookup of precomputed hashes. Dictionary attacks with rules leverage common password patterns and are computationally cheap. Together, they quickly identify weak passwords without the enormous resource expenditure of brute-force or massive precomputation. They are the most effective and resource-conscious choices.

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Precomputed hash tables for all possible 8-character passwords.

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Hybrid attack combining a wordlist with a mask for appended digits.

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Brute-force attack using the full NTLM character set up to 12 characters.

Question 8

A penetration tester extracts a password hash from a database that starts with $2y$10$. Which statement correctly identifies the algorithm and a key characteristic?

Accepted Answer

It is a bcrypt hash, and the cost factor is 10, meaning 2^10 iterations.. The $2y$ prefix identifies the hash as bcrypt, and the following number is the cost factor (log2 of iterations). A cost of 10 means 2^10 = 1024 iterations. Bcrypt is a deliberate slow hashing algorithm used to protect passwords. Other prefixes like $6$ for SHA-512 crypt, $1$ for MD5 crypt, and $7$ for scrypt are different. Correct identification is crucial for selecting the right cracking mode and understanding the computational effort required.

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It is a SHA-512 crypt hash, and the number 10 is the salt length.

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It is an MD5 crypt hash, and the number 10 is the iteration count.

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It is a scrypt hash, and the number 10 is the memory cost parameter.

Question 9

You are performing an offline attack against a password hash stored in an NTDS.dit file. You have successfully dumped the hashes using secretsdump.py. Given the format 'Username:RID:LMHash:NTHash:::', which hash should be targeted for a modern Windows environment to maximize cracking efficiency?

Accepted Answer

The NTHash, because it is the primary hash used by NTLM authentication.. Modern Windows systems prioritize NTLM authentication, which relies on the NTHash. The LM hash is deprecated, weak, and often stored as a null value or a fixed constant in modern systems. Targeting the NTHash allows for pass-the-hash attacks or brute-force attempts that align with the underlying authentication protocol. Understanding the structure of these hashes is crucial for penetration testers to select the correct dictionary or mask attack strategies during local account auditing.

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The LMHash, because it is shorter and faster to calculate.

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The RID, because it provides the unique identifier for the account.

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The entire string, including the colons, to ensure format integrity.

Question 10

Which TWO of the following password cracking techniques are considered 'offline' attacks?

Accepted Answer

Running a dictionary attack against a SAM database file.. Offline attacks involve obtaining a copy of the password hashes and processing them on the attacker's own hardware. This is stealthy as it avoids account lockout policies and audit logging generated by failed login attempts on the target system. Understanding the distinction between online and offline attacks is vital for penetration testers to choose methods that minimize detection while maximizing the probability of successful credential recovery within a controlled and limited engagement timeframe.

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Brute-forcing an SSH service via an internet-facing portal.

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Spraying common passwords against an O365 login portal.

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Phishing users to submit credentials into a fake form.