North Korean APT37 Hackers Use VBA Self Decode Technique to Inject RokRat

A North Korean hacking group known as ScarCruft, Reaper and Group123 has been involved in targeting the South Korean government by using a VBA self-decode technique to inject RokRat.

What is RokRat?

RokRat is a Remote Access Trojan(RAT) and is a sophisticated backdoor commonly distributed as an encoded binary file, downloaded and decrypted by shellcode following the exploitation of weaponized documents. RokRat is skilled at evasion and utilizes multiple techniques to make detection difficult and time-consuming.

The Attack History

On December 7, 2020, a malicious document uploaded to Virus Total was identified. The document pretended to be a meeting request, and it is believed the intended target of the attack was the South Korean government. 23 January 2020 is the meeting date mentioned in the document and this aligns with the document compilation date of 27 January 2020. This shows that the attack had taken place a year back.

The Interesting way how RokRat Attack Works

An embedded macro is contained in the malicious file, and this uses a VBA self-decoding technique to decode itself within memory spaces of Microsoft Office without writing to the disk. Once this is done, it then embeds a variant of the RokRat to Notepad.

Researchers believed that this sample is associated with APT37, a suspected North Korean cyber espionage group, basis the injected payload.  In the past, this APT has relied on Hangul Office documents (hwp files) to target victims, as it’s software that’s commonly used in South Korea.

Spear phishing was the primary initial infection vector used by APT37. An email is sent to the target to weaponize the malicious document.

Spear Phishing is a malicious practice that execute via Email campaigns that hackers research their target audience, understand their likes and dislikes, study their day to day operations, and customize the mail to steal the sensitive data and install malware.

Usually Hwp files (Hangul Office) are used to weaponize with a self-decode macro. However, this time Microsoft Office file have been used. In the past too, the RokRat malware has targeted several high profile public figures including Donald Trump, Hillary Clinton and several others.

This attack was carried out for political purposes. In this campaign, the malware was delivered via malspam email campaigns with fake body content relating to bank frauds.

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