There is one malicious thing they can do, they can end your connection, or degrade it. Two. That's two malicious things

If we are thinking about the "CIA" model, the confidentiality and integrity of the system are maintained, but surely the availability of the system is still at risk?

Yes, DoS attacks being the common example... Perhaps the problem is more when an attacker can compromise your availability, whereas in this case, there is no attacker, the lack of availability is fully within your control.

Isn't availability considered one of the pillars of security?

@Michael while that's true, it looks like this won't force corporate proxies to change, they will still be able to use local, see third paragraph: chromium.org/Home/chromium-security/root-ca-policy

My question from 3 years ago, which I was never satisfied with, is very related: security.stackexchange.com/questions/165706/…

@fraxinus I can't think of anything the plumber will gain by making your water heater leak.

How much of this can be mitigated by locking your computer?

Just give your password a +2 shield and that should just about cancel out the advan- oh sorry wrong stack...

Free overtime is giving yourself a bad deal. Why do you think because OP has one very small part of their job to do security-related things, that they would want to change their entire career path based on it?

To read about one man's attempt: wired.com/2009/11/ff-vanish2

Many of you are thinking from the perspective of validating passwords for yourself. But that is not the only time you need to validate passwords - you may have to validate passwords for others, for instance users of your site, or of your organisation. In retrospect I should have made that more clear from my question that that was my case. Oh well it is too late now.

This answer seems to best sum up what I have learned from the answers and comments on this question. Thanks Kristopher