Pierluigi Paganini March 08, 2023

North Korea-linked Lazarus APT group exploits a zero-day vulnerability in attacks aimed at a South Korean financial entity.

ASEC (AhnLab Security Emergency Response Center) observed North Korea-linked Lazarus APT group exploiting a zero-day vulnerability in an undisclosed software to breach a financial business entity in South Korea. The nation-state actors breached twice the company in one year.

The first attack was spotted in May 2022, threat actors targeted a vulnerable version of a certificate software that’s widely used by public institutions and universities in South Korea.

A second attack was observed in October 2022, when attackers exploited a zero-day vulnerability affecting the same software.

“During the infiltration in May 2022, the affected company was using a vulnerable version of a certificate program that was commonly used by public institutions and universities. After the incident, they updated all of their software to their latest versions.” reads the advisory published by the ASEC. “However, the Lazarus group used the software’s 0-Day vulnerability to carry out their infiltration this time.”

ASEC reported the zero-day to KISA, it also pointed out that the vulnerability has not been fully verified yet and a software patch has yet to be released.

The Lazarus APT exploited the zero-day flaw to conduct lateral movement, it also disabled the anti-malware software by using the technique known as Bring Your Own Vulnerable Driver (BYOVD).

This isn’t the first that the Lazarus APT used the BYOVD technique, in October 2022 the North Korea-linked group has been spotted deploying a Windows rootkit by taking advantage of an exploit in a Dell firmware driver.

ASEC also noticed that the APT employed anti-forensic techniques to hide their malicious activities, such as changing filenames before deleting them or modifying time stamps.

The researchers analyzed two PCs of the target organization and confirmed that the threat actor had performed a lateral movement attack on PC01 and PC02 using the certificate software’s vulnerability. 

The attackers created the backdoor loader (LegacyUserManager.dll) to deploy the following malicious payloads:

• C:\ProgramData\Microsoft\Crypto\Keys\Keys.dat (obtained)
• C:\ProgramData\Microsoft\Settings\Settings.vwx (obtained)

“The threat actor exploited the 0-Day vulnerability of a certificate software that is commonly used in Korea. Since these types of software are not updated automatically, they must be manually patched to the latest version or deleted if unused. ” ASEC concludes. “The affected company was re-infiltrated by the same threat actor with a similar method. Instead of taking only post-attack measures, continuous monitoring is required to prevent recurrences.”

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Pierluigi Paganini

(SecurityAffairs – hacking, Moshen Dragon)