A while back I wrote about a bunch of vulnerabilities in McAfee WebAdvisor, a component of McAfee antivirus products which is also available as a stand-alone application. Part of the fix was adding a bunch of pages to the extension which were previously hosted on siteadvisor.com, generally a good move. However, when I looked closely I noticed a Cross-Site Scripting (XSS) vulnerability in one of these pages (CVE-2019-3670).
Now an XSS vulnerability in a browser extension is usually very hard to exploit thanks to security mechanisms like Content Security Policy and sandboxing. These mechanisms were intact for McAfee WebAdvisor and I didn’t manage to circumvent them. Yet I still ended up with a proof of concept that demonstrated how attackers could gain local administrator privileges through this vulnerability, something that came as a huge surprise to me as well.