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Mysterious 'AcidBox' Malware Used Turla Exploit to Target Russian Organizations

Targeted attacks delivering a new piece of malware leveraged an exploit previously associated with the Russian-linked Turla hacking group, Palo Alto Networks reveals.

Believed to be operating on behalf of the Russian Federal Security Service (FSB) and also known as Waterbug, Venomous Bear and KRYPTON, Turla was the first threat actor known to have abused a third-party device driver to disable Driver Signature Enforcement (DSE), a security feature introduced in Windows Vista to prevent the loading of unsigned drivers.

Often referred to as CVE-2008-3431, Turla’s exploit, which targeted a signed VirtualBox driver (VBoxDrv.sys v1.6.2) to deactivate DSE and load unsigned payload drivers, actually abused two vulnerabilities, but only one was addressed. A second version of the exploit targets the unknown vulnerability only.

Now, Palo Alto Networks reveals that the same unpatched security flaw is being abused by an unknown threat actor unrelated to Turla, to exploit newer versions of the VirtualBox VBoxDrv.sys driver as well.

The adversary targeted at least two different Russian organizations in 2017 by exploiting version 2.2.0 of the driver, likely because this iteration wasn’t known to be vulnerable. The attackers deployed a previously unknown malware family, which the researchers named AcidBox.

“Since no other victims have been found, we believe this is a very rare malware used in targeted attacks only,” Palo Alto Networks says.

A complex piece of malware part of a bigger toolset, AcidBox is likely associated with an advanced threat actor and might still be in use today, provided that the attacker is still active.

“However, we anticipate that it was rewritten to a certain extent. Based on the information we have, we don’t believe this unknown threat actor is tied to Turla, except for the used exploit,” Palo Alto Networks, which provides a detailed analysis of the malware, says.

Working with other security companies, the researchers identified three usermode samples of the malware (64-bit DLLs that load the main worker from the Windows registry), and a kernelmode payload driver (which is embedded in the main worker sample).

All samples feature a compilation timestamp of May 9, 2017, and were likely used in a campaign the same year. No newer samples have been found and it’s unclear whether the threat actor is still active.

AcidBox, which appends sensitive data as an overlay in icon resources, abuses the SSP interface for persistence and injection, stores its payload in the Windows registry, and doesn’t show any clear overlaps with publicly-known malware, although it shows loose similarities to Remsec.

Palo Alto Networks could not identify the toolkit that AcidBox is part of, but the company has shared two YARA rules for detection and threat hunting, along with a Python script that can help victims extract the sensitive data appended to the icon resources.

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