Newly discovered ransomware uses BitLocker to encrypt victim data

A beforehand unknown piece of ransomware, dubbed ShrinkLocker, encrypts sufferer knowledge utilizing the BitLocker function constructed into the Home windows working system.

BitLocker is a full-volume encryptor that debuted in 2007 with the discharge of Home windows Vista. Customers make use of it to encrypt total arduous drives to forestall folks from studying or modifying knowledge within the occasion they get bodily entry to the disk. Beginning with the rollout of Windows 10, BitLocker by default has used the 128-bit and 256-bit XTS-AES encryption algorithm, giving the function further safety from assaults that depend on manipulating cipher textual content to trigger predictable adjustments in plain textual content.

Lately, researchers from safety agency Kaspersky discovered a risk actor utilizing BitLocker to encrypt knowledge on programs situated in Mexico, Indonesia, and Jordan. The researchers named the brand new ransomware ShrinkLocker, each for its use of BitLocker and since it shrinks the scale of every non-boot partition by 100 MB and splits the newly unallocated house into new main partitions of the identical measurement.

“Our incident response and malware evaluation are proof that attackers are continually refining their techniques to evade detection,” the researchers wrote Friday. “On this incident, we noticed the abuse of the native BitLocker function for unauthorized knowledge encryption.”

ShrinkLocker isn’t the primary malware to leverage BitLocker. In 2022, Microsoft reported that ransomware attackers with a nexus to Iran additionally used the device to encrypt recordsdata. That very same 12 months, the Russian agricultural enterprise Miratorg was attacked by ransomware that used BitLocker to encrypt recordsdata residing within the system storage of contaminated gadgets.

As soon as put in on a tool, ShrinkLocker runs a VisualBasic script that first invokes the Home windows Administration Instrumentation and Win32_OperatingSystem class to acquire details about the working system.

“For every object throughout the question outcomes, the script checks if the present area is totally different from the goal,” the Kaspersky researchers wrote. “Whether it is, the script finishes robotically. After that, it checks if the title of the working system accommodates ‘xp,’ ‘2000,’ ‘2003,’ or ‘vista,’ and if the Home windows model matches any certainly one of these, the script finishes robotically and deletes itself.”

The script then continues to make use of the WMI for querying details about the OS. It goes on to carry out the disk resizing operations, which may fluctuate relying on the OS model detected. The ransomware performs these operations solely on native, mounted drives. The choice to go away community drives alone is probably going motivated by the need to not set off community detection protections.

Finally, ShrinkLocker disables protections designed to safe the BitLocker encryption key and goes on to delete them. It then permits using a numerical password, each as a protector towards anybody else taking again management of BitLocker and as an encryptor for system knowledge. The rationale for deleting the default protectors is to disable key restoration options by the system proprietor. ShrinkLocker then goes on to generate a 64-character encryption key utilizing random multiplication and alternative of:

• A variable with the numbers 0–9;
• The well-known pangram, “The fast brown fox jumps over the lazy canine,” in lowercase and uppercase, which accommodates each letter of the English alphabet;
• Particular characters.

After a number of extra steps, knowledge is encrypted. The subsequent time the system reboots, the show seems to be like this:

Decrypting drives with out the attacker-supplied secret is tough and certain unattainable in lots of circumstances. Whereas it’s doable to get better among the passphrases and glued values used to generate the keys, the script makes use of variable values which are totally different on every contaminated system. These variable values aren’t straightforward to get better.

There aren’t any protections particular to ShrinkLocker for stopping profitable assaults. Kaspersky advises the next:

• Use strong, correctly configured endpoint safety to detect threats that attempt to abuse BitLocker;
• Implement Managed Detection and Response (MDR) to proactively scan for threats;
• If BitLocker is enabled, be certain that it makes use of a robust password and that the restoration keys are saved in a safe location;
• Make sure that customers have solely minimal privileges. This prevents them from enabling encryption options or altering registry keys on their very own;
• Allow community site visitors logging and monitoring. Configure the logging of each GET and POST requests. In case of an infection, the requests made to the attacker’s area could include passwords or keys;
• Monitor for occasions related to VBS execution and PowerShell, then save the logged scripts and instructions to an exterior repository storing exercise which may be deleted regionally;
• Make backups regularly, retailer them offline, and take a look at them.

Friday’s report additionally consists of indicators that organizations can use to find out if they’ve been focused by ShrinkLocker.

Itemizing picture by Getty Images