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How Do Pass-the-hash Attacks Work?

by | Oct 12, 2021 | BLOG

Despite being something old, from the 1990s, few people know how pass-the-hash attacks work.

Keep reading the article to find out!

Where Did the Name “Pass-the-hash” Come From?

Pass-the-hash attacks occur when an attacker steals a user’s credential with a hash function.

Without “breaking” this function, the attacker reuses it to trick an authentication system into creating a new authenticated session on the same network.

For those who are not aware of it, a hash function is any algorithm that maps large, variable-sized data to small, fixed-sized data.

Hash functions are widely used in order to verify the integrity of downloads, search for elements in databases, or transmit and store passwords.

Hence the “pass-the-hash” name, which literally means this—exactly what attackers do through this attack.

How Are Pass-the-hash Attacks in Information Technology Classified?

Pass-the-hash attacks are primarily a lateral movement technique.

This means hackers are using the hash to extract additional information and credentials after they have already compromised a device.

By moving “sideways” between devices and accounts, attackers can “pass the hash” to get all the correct credentials from someone else.

With this, they can eventually “scale up” their domain privileges and access more influential systems, like an administrator account on their personal computer, without even needing their password.

Another interesting fact is that most of the movement performed during a pass-the-hash attack uses a remote software program, such as malware.

What Operating Systems Do Pass-the-hash Attacks Work On?

Typically, pass-the-hash attacks target Windows systems.

However, they can also work against other operating systems, in some cases on any authentication protocol such as Kerberos.

Windows is especially vulnerable to these attacks because of its single sign-on function.

This function allows users who, by entering the password only once, can access all the features they want.

The single sign-on function also requires users’ credentials to be cached on the system, making it easier for attackers to access.

That is one of the reasons why it is so important to know the 7 Tips to Prevent Cyberattacks While Remote Working.

How Do Pass-the-hash Attacks Work?

To perform a pass-the-hash attack, the attacker first obtains the hashes of the targeted system using any number of hash dump tools, such as fgdump and pwdump7.

The attacker then uses these tools to place the obtained hashes into a Local Security Authority Subsystem Service (LSASS).

Pass-the-hash attacks are often targeted at Windows machines due to the security vulnerability of NTLM (New Technology Local Area Network Manager) hashes once administrator privileges have been obtained.

These attacks often trick a Windows-based authentication system into “believing” that the attacker’s endpoint is the legitimate user’s endpoint.

Thus, the system automatically supplies the necessary credentials when the attacker tries to access the targeted system.

And all this can be done, as already said, without the need for the original password.

The key used by attackers to perform these types of attacks is the NTLM hash, which is nothing more than fixed-length mathematical codes derived from passwords.

NTLM hashes allow the attacker to use compromised domain accounts without extracting the password in plain text.

This is because computer operating systems such as Windows never actually send or save user passwords on their network.

Instead, these systems store passwords as encrypted NTLM hashes, which represent the password, but cannot be reverse-engineered.

NTLM hashes can still be used in place of a password to access various accounts and resources on the network.

For an attacker to be able to access LSASS, they must successfully compromise a computer to the point where the malware can run with local administrator rights.

Therefore, this is one of the biggest obstacles to pass-the-hash attacks. And knowing how to securely control your privileged accounts with PEDM is another big obstacle, too.

Once a Windows-based machine is compromised and the deployed malware is given access to local usernames and NTLM hashes, do you know what happens?

The attacker can even choose whether to get more credentials or try to access network resources using privileged user credentials.

By gathering more user credentials, an attacker can retrieve the credentials of users who have separate accounts on the Windows machine, such as a service account, or who still have remote access to the computer with an administrator login, for example.

Remote information technology (IT) administrators connecting to the compromised Windows machine will expose their NTLM username and hash to the now-integrated malware.

An attacker with IT administrator credentials can then move “sideways” across networked devices.

The “lateral movement” is an effective way to search for users with elevated privileges, such as administrative rights to protected resources.

Privilege escalation can be achieved by locating the credentials of an administrator with greater administrative access.

These elevated features can also include access to customer databases and email servers.

What Can Pass-the-hash Attacks Do to My Computer?

Because this type of attack exploits the features and capabilities of the NTLM protocol, the threat can never be completely eliminated.

Once an attacker compromises a computer, pass-the-hash becomes just one of the malicious activities that can be performed.

A 2019 study found that 95% of its 1,000 respondents experienced a direct business effect from pass-the-hash in their organizations.

About 40% of these attacks resulted in lost revenue and 70% incurred increased operational costs.

No wonder that many IT experts consider pass-the-hash attacks to be among the top cybersecurity vulnerabilities in Industry 4.0.

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How to Avoid Pass-the-hash Attacks?

Unfortunately, there are many ways for hackers to remotely compromise a computer, and they are constantly evolving.

For this reason, cybersecurity measures will never be 100% effective, which is why multiple mitigation techniques are often used at the same time.

Recognizing that even knowing how pass-the-hash attacks work cannot prevent them all, companies can try to improve their detection strategies as well as their prevention measures.

Workstation logs are one of the most common ways to reliably monitor administrative activities.

These logs can track privilege assignments as well as successful login attempts.

Target server logs and domain controller logs are useful for the same reasons.

To mitigate the threat of pass-the-hash attacks, organizations must also ensure that domain controllers can only be accessed from trusted systems without Internet access.

Two-factor authentication using tokens should also be applied, as well as the principle of least privilege — in that sense, adopting Zero Standing Privileges (ZSP) is an option.

Organizations must closely monitor hosts and traffic on their networks for suspicious activity.

Request a free demo of cybersecurity services right now and stay protected from these types of threats!



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