In the aftermath of the Itaewon Halloween crowd crush that killed at least 158 people, North Korea’s APT37 state-sponsored hacking group took advantage of a previously unknown Internet Explorer vulnerability to install malware on the devices of South Koreans who were trying to find out about the tragedy, according to Google’s Threat Analysis Group. The team became aware of the recent attack on October 31st after multiple South Koreans uploaded a malicious Microsoft Office document to the company’s VirusTotal tool.

APT37 took advantage of national interest in the Itaewon tragedy by referencing the event in an official-looking document. Once someone opened the doc on their device, it would download a rich text file remote template that would, in turn, render remote HTML using Internet Explorer. According to Google, this is a technique that has been widely used to distribute exploits since 2017, as it allows hackers to take advantage of vulnerabilities in Internet Explorer even if someone isn’t using IE as their default web browser.

The JavaScript vulnerability APT37 took advantage of allowed the group to execute arbitrary code. Google informed Microsoft of the zero-day on the same day it became aware of it. On November 8th, Microsoft released a software update to address the exploit. “We’d be remiss if we did not acknowledge the quick response and patching of this vulnerability by the Microsoft team,” Google said.

While the TAG team didn’t get a chance to analyze the final malware APT37 hackers attempted to deploy against their targets, it notes the group is known for using a wide variety of malicious software, including ROKRAT, BLUELIGHT and DOLPHIN. “TAG also identified other documents likely exploiting the same vulnerability and with similar targeting, which may be part of the same campaign,” the team added.

This isn’t the first time Google’s Threat Analysis Group has thwarted an attack by North Korean hackers. At the start of 2021, the team detailed a campaign that targeted security researchers. More recently, the team worked with the Chrome team to address a vulnerability that was used by two North Korean hacking cadres to execute remote code.