On April 14-15, 2021, Kaspersky technologies detected a wave of highly targeted attacks against multiple companies. Closer analysis revealed that all these attacks exploited a chain of Google Chrome and Microsoft Windows zero-day exploits. While we were not able to retrieve the exploit used for remote code execution (RCE) in the Chrome web browser, we were able to find and analyze an elevation of privilege (EoP) exploit that was used to escape the sandbox and obtain system privileges.
The elevation of privilege exploit was fine-tuned to work against the latest and most prominent builds of Windows 10 (17763 – RS5, 18362 – 19H1, 18363 – 19H2, 19041 – 20H1, 19042 – 20H2) and it exploits two distinct vulnerabilities in the Microsoft Windows OS kernel. On April 20, 2021, we reported these vulnerabilities to Microsoft and they assigned CVE-2021-31955 to the information disclosure vulnerability and CVE-2021-31956 to the elevation of privilege vulnerability. Both vulnerabilities were patched on June 8, 2021, as a part of the June Patch Tuesday.
Remote code execution exploit
All of the observed attacks were conducted through Chrome browser. Unfortunately, we were unable to retrieve the JavaScript with full exploit code, but the timeframe of attacks and events preceding it led us to suspect one particular vulnerability.
On April 6-8, 2021 the Pwn2Own competition took place. This is a computer hacking contest where the Google Chrome web browser was one of the targets. According to the ZDI (Zero Day Initiative, the organizer of Pwn2Own) website, one participating team was able to demonstrate a successful exploitation of the Chrome renderer process using a Typer Mismatch bug.
On April 12, 2021, the developers of Chromium committed two (issue 1196683, issue puzzlemaker threat group attacks chrome exploit chain
