User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/84.0.4147.105 Safari/537.36

Steps to reproduce:

Hi Team,

Over the last 1-2 weeks we have been chasing down a malvertising campaign that is running via native ads on high profile publishers.

Once victims land on the malicious landing page, they are presented with a tech support scam.

The landing page itself contains a "browlock" mechanism that will crash or significantly stall recent versions of most modern browsers including Chrome, FireFox, Opera, and Brave.

Attached is a screenshot of the malicious landing page for context, along with a distilled POC that produces the browlock.

We've found that this tactic produces a significant slow down of browser responsiveness within 5-30 seconds, often leading to a complete freeze that requires killing the browser process in order to unlock.

In conjunction with the infinite pushState loop, this attacker also hides the pointer in a nested pointerlock loop which effectively buys some time for the browlock to go into full effect.

Given the persistence and broad reach of these malvertisers, this browlock is likely impacting a pretty large swath of users.

Hopefully this can somehow be mitigated in a future release of Firefox.

Best,
Eliya Stein