AV software is a great target for malware, badly written, probably runs too much stuff in the kernel, tries to parse everything
I think most AV companies now have a helper process to do that.
If you successfully exploit the helper process, the worst damage you ought to be able to do is falsely find files to be clean.
Ought. But it depends on the way the communication with the main process is done. I wouldn't be surprised if the main process trusts the output from the parser just a tiny bit too much.