Zerologon Case Study: How One Vulnerability Put the World's Corporate Networks at Risk

[Cloned Boy]

Zerologon (CVE-2020-1472) is a critical vulnerability in the Windows Server Netlogon protocol discovered in 2020. It allowed hackers to compromise Active Directory (AD) domain controllers in seconds without a password.

What is Zerologon?​

Technical essence of the vulnerability​

• Where? In the Netlogon protocol (used for authentication in Windows domains).
• Problem: Cryptography error (AES-CFB8 with incorrect IV check).
• Result: It is possible to forge a request and obtain domain administrator rights.

How did it work?​

1. The hacker sent a special request to the domain controller.
2. The server did not verify the authenticity of the request due to an encryption bug.
3. The attacker gained full control over the domain (including all computers and accounts).

Who used Zerologon?​

1. Cybercriminals​

• Ransomware groups (Conti, Ryuk) hacked corporate networks and encrypted data.
• Financial predators stole logins from banking systems.

2. State hackers​

• Chinese APT groups have attacked US government networks.
• Russian hackers (such as Cozy Bear) used Zerologon for stealth access.

3. Script-kiddie​

Due to the ease of exploitation (there is a ready-made PoC in Metasploit), the vulnerability has become widespread.

How was the vulnerability discovered and fixed?​

1. Who found it?​

• Researchers from Secura (Netherlands) in August 2020.

2. Microsoft's reaction​

• August 2020: Urgent patch (but many have not updated).
• February 2021: Forced shutdown of vulnerable version of Netlogon.

3. Difficulty in correction​

• Old devices (printers, IoT) broke after the update.
• Some companies are still vulnerable (according to CISA).

Zerologon Consequences​

1. Global hacks​

• Hospitals, banks, government agencies were attacked via Zerologon.
• Losses: Tens of millions of dollars (due to ransomware).

2. Security Changes​

• Active Directory now requires strong authentication.
• Cyber insurance has become more expensive for companies with legacy systems.

3. A lesson for the industry​

• Even "innocent" protocols can be dangerous.
• Automatic update is a must.

What did this case teach us?​

1. One line of code can break all security.
2. Old systems = prime target for hackers.
3. Even Microsoft isn't always quick to fix holes.

Want another vulnerability analyzed? For example, Log4Shell — how a Java library bug shook the internet?