Windows, IE11 Zero-Day Vulnerabilities Chained In Targeted Attack

Windows, IE11 Zero-Day Vulnerabilities Chained In Targeted Attack

An advanced threat actor exploited one of the two zero-day vulnerabilities that Microsoft patched on Tuesday in a targeted attack earlier this year.

The adversary chained two flaws in Windows, both unknown at the time of the attack, in an attempt to achieve remote code execution and increase their privileges on a compromised machine.

IE – the door to Windows 10

The malicious endeavor occurred in May and targeted a South Korean company. Researchers from Kaspersky believe that this may be a DarkHotel operation, a hacker group likely operating in one form or another for more than a decade.

Dubbed “Operation PowerFall,” the attack relied on a remote code execution (RCE) vulnerability in Internet Explorer 11, now tracked as CVE-2020-1380, and a flaw in Windows GDI Print/Print Spooler API allowing privilege escalation, now identified as CVE-2020-0986.

The RCE bug is a use-after-free in the JavaScript engine in Internet Explorer starting version 9. IE 11 continues to be present on Windows 10 to support applications that rely on it for various features (e.g. Microsoft Office, to show video content embedded in documents).

Boris Larin of Kaspersky, who discovered and reported CVE-2020-1380 to Microsoft on June 8, released today proof-of-concept code to trigger the vulnerability along with a technical explanation to help understand it better.

Although the severity score by the Common Vulnerability Scoring System (CVSS) is 7.5 out of 10, Microsoft rated it as critical for Windows 10 machines.

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Actor quickly used 0day details

After getting remote access to the target machine, the threat actor used a module that created a file named “ok.exe,” which leverages CVE-2020-0986 to run malicious code with elevated privileges.

Microsoft received a report for this vulnerability in December 2019 from an anonymous source, via Trend Micro’s Zero Day Initiative (ZDI), but delayed releasing a patch until June 9.

After half a year of inaction from Microsoft, ZDI published an advisory on May 19, 2020. Larin says that the issue was exploited the very next day by the actors behind Operation PowerFall.

The attack was detected and blocked by Kaspersky technology before the payload landed on the compromised machine, which denied researchers that opportunity to analyze it and possibly link it to a known adversary.

Nevertheless, the exploits have some similarities with others analyzed in the past and suggest that DarkHotel may be involved.

While there is little data to determine the initial infection vector, Larin told BleepingComputer that “exploitation with a malicious Office document might be possible because MS Office uses IE to display web-content.”

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