As most people know, Microsoft essentially gave up on Explorer after it failed to gain ground against its major competitors in the browser ecosystem. They started fresh, with Microsoft Edge, designed as a modern replacement.
Unfortunately, there are still legions of faithful IE users hanging on, and they are at risk. The company recently received a notification from Google's Threat Analysis Group alerting them to the presence of the flaw, which centers around the way the software's scripting engine handles objects in memory.
Worse, although the company did not provide any details, a separately published advisory on the topic made clear that this flaw has been seen in the wild and is actively being used by hackers.
The issue is so severe that Microsoft broke with its own policy and issued an emergency update to fix the flaw for IE holdout users. If, for whatever reason, you have yet to switch to some other browser, this is one security update you won't want to miss. You'll find it on the company's website indexed as CVE-2018-8653. The company has also made clear that there are no known workarounds for this issue, except to install the latest patch.
Ultimately, of course, the best solution would be to seriously consider migrating away from the use of Internet Explorer. Microsoft will likely continue to issue emergency patches as other issues are discovered. Unfortunately though, they have formally ended support for the product, so there's no guarantee. Every day you continue using the outdated browser, you put yourself at unnecessary and entirely avoidable risk.
If you haven't already got firm plans in place to migrate to some other browser, this is one more in a long list of compelling reasons to make it a priority.