ShrinkLocker (Ransomware) – Malware

Overview

A new ransomware variant called ShrinkLocker exploits Windows BitLocker to encrypt corporate systems by creating a new boot partition and shrinking available non-boot partitions to maximize damage. Developed in Visual Basic Scripting (VBScript), ShrinkLocker uses the diskpart utility to resize partitions, BCDEdit to reinstall boot files, and modifies registry entries to disable remote desktop connections and enable BitLocker encryption. Instead of leaving a ransom note, the attacker provides a contact email address and deletes BitLocker protectors to prevent recovery. ShrinkLocker uses a subtle email label on recovery screens, potentially indicating a motive of destruction rather than financial gain. Multiple variants of this ransomware have targeted government entities and companies. As a response, experts recommend securing backup strategies, managing BitLocker recovery keys, deploying Endpoint Protection Platforms (EPP), and enforcing strict access controls to mitigate the threat. Kaspersky dubbed the script “ShrinkLocker,” as this name highlights the critical procedure of partition resizing, which is essential for ensuring the system boots correctly with the encrypted files.

Targets

Organizations in the steel and vaccine manufacturing sectors, as well as government entities

How they operate

According to Kaspersky’s Global Emergency Response team, threat actors are using VBScript—a programming language for automating tasks on Windows computers—to create a malicious script with previously unreported features to maximize attack damage. The script’s novelty lies in its ability to check the current Windows version and enable BitLocker features accordingly, allowing it to infect both new and legacy systems back to Windows Server 2008. If the operating system version is suitable for the attack, the script alters boot settings and attempts to encrypt entire drives using BitLocker. It establishes a new boot partition, setting up a separate section on the drive containing files necessary for booting the operating system, aimed at locking the victim out. Additionally, the attackers delete protectors securing BitLocker’s encryption key, preventing recovery. The malicious script also sends information about the system and the generated encryption key to a server controlled by the threat actor. To cover its tracks, the script deletes logs and various files that could aid in investigating the attack. As a final step, the malware forces a system shutdown, facilitated by creating and reinstalling files in the separate boot partition. Upon reboot, the victim sees the BitLocker screen with the message: “There are no more BitLocker recovery options on your PC.”  

Significant Malware Campaigns

• Kaspersky has identified ransomware attacks using Microsoft’s BitLocker to attempt encryption of corporate files. The incidents with this ransomware, dubbed “ShrinkLocker,” and its variants were observed in Mexico, Indonesia, and Jordan. (May 2024)

References:

• Kaspersky uncovers new BitLocker-abusing ransomware
• ShrinkLocker: Turning BitLocker into ransomware
• New ShrinkLocker ransomware uses BitLocker to encrypt your files