From https://arstechnica.com/information-technology/2017/11/how-av-can-open-you-to-attacks-that-otherwise-wouldnt-be-possible/:

Antivirus programs, in many cases, make us safer on the Internet. Other times, they open us to attacks that otherwise wouldn't be possible. On Friday, a researcher documented an example of the latter—a vulnerability he found in about a dozen name-brand AV programs that allows attackers who already have a toehold on a targeted computer to gain complete system control.