A critical vulnerability in Microsoft’s Netlogon Remote Protocol (CVE-2020-1472), widely known as “ZeroLogon,” has emerged as a key target for ransomware groups, enabling attackers to gain unauthorized control over Windows Active Directory domain controllers.
This flaw, which stems from cryptographic weaknesses in the protocol, has been exploited to escalate privileges and deploy ransomware across enterprise networks, posing severe risks to organizational security.
Exploitation Techniques
The ZeroLogon vulnerability arises from improper implementation of the AES-CFB8 cryptographic algorithm in the Netlogon protocol.
Specifically, the initialization vector (IV) is set to a fixed value of 16 zero bytes, creating a cryptographic flaw.
Attackers can exploit this by sending specially crafted authentication requests with zeroed fields, bypassing security checks.
With an average of 256 attempts, they can establish an unsecure Netlogon session and reset the domain controller’s machine account password to a blank value.
Once access is gained, attackers can escalate privileges to domain administrator levels, allowing them to manipulate security policies, disable defenses, and move laterally across the network.
This vulnerability has been weaponized by ransomware groups such as RansomHub, which use it as an entry point for deploying malicious payloads and encrypting critical data.
Ransomware Deployment
Ransomware operators leverage ZeroLogon to execute multi-stage attacks. After compromising the domain controller, they disable endpoint detection and response (EDR) tools using utilities like PCHunter or EDRKillShifter.
Subsequently, ransomware is deployed to encrypt files on local and networked drives.
In some cases, attackers exfiltrate sensitive data before encryption, threatening victims with public disclosure unless a ransom is paid.
Groups like RansomHub have exploited ZeroLogon in high-profile attacks targeting sectors such as healthcare, finance, and critical infrastructure.
The vulnerability’s ease of exploitation requiring no authentication or elevated privileges has made it a favored tactic among cybercriminals.
Microsoft released patches addressing ZeroLogon in August 2020 as part of its Patch Tuesday updates.
According to the Group-IB, the fix includes enforcing secure RPC communication for Netlogon sessions.
A second update in February 2021 mandated secure RPC connections across all devices interacting with domain controllers.
Organizations are strongly advised to apply these patches immediately to mitigate risks.
Additionally, administrators should monitor network activity for signs of exploitation.
Indicators include anomalous Netlogon traffic or event IDs such as 4742 (account changes) and 5829 (vulnerable Netlogon connections).
Tools like Microsoft Defender for Identity can detect ZeroLogon exploitation attempts in real-time.
The ZeroLogon vulnerability underscores the critical importance of timely patch management and proactive monitoring in securing enterprise networks.
As ransomware groups continue to exploit known vulnerabilities like CVE-2020-1472, organizations must prioritize patching domain controllers and implementing robust detection mechanisms to safeguard against such devastating attacks.
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