See this pastebin[1] for the function I believe is determining the url of the active tab and if it has a valid hostname.
There's also this one[2] that seems to be extracting the hostname of a given url also using the URL API.
Both these pastebins contain minimized code that I've cleaned up.
0: https://developer.mozilla.org/en-US/docs/Web/API/URL
LastPass (on Chrome) will auto-fill information on a detected site, which a malicious site can read immediately.
1Password (on Chromium nightly) requires me to hit the 1Password Mini button and select a site/account to log in with. If 1Password had a similar vulnerability, a malicious site as described would merely wind up showing me accounts for the wrong site in the dropdown. Clicking one could wind up submitting/leaking my credentials to the attacker, though.
This is actually how I use 1Password most often. Global hotkey of cmd+opt+\, type a site name, hit enter: 1Password opens the site and logs in.
I think an official word holds more clout and is more valuable than any one person confirming for themselves in one version of one browser on one version of one OS.
I understand that, as a user of 1Password's browser extension(s), you may well feel some concern that a similar vulnerability exists, and I don't think it's unreasonable to want reassurance on that score.
But I think your phrasing and framing of the question feels a lot more like a "gotcha" than anything else, and it's that feeling which motivated my prior comment - I'm not an AgileBits dev myself, but if I were, I'd feel strongly inclined to shy away from that question rather than trying to frame an answer that doesn't leave me open to a potentially hostile followup.
Presumably that's the job of a professional security developer that might reasonably be expected to have checked their own similar product for this vulnerability...
