Per Bleeping Computer CVE-2021-21193 is the second of the three bugs to be actively exploited. It’s described as a use after free bug in the open source browser-rendering engine Blink and could result in arbitrary code execution, and possibly tears. Google’s not sharing much more til it gets patches out. Its other two friends are CVE-2021-21166 and CVE-2021-2114, which you probably want to look further into if you haven’t already.