User provided content (post using custom emojis) caused havoc when processing (doesn’t matter if on server or on client). This is lack of sanitization of user-provided-data.

100%. Always act as though user provided content is malicious.

JavaScript (TypeScript) has access to cookies (and thus JWT). This should be handled by web browser, not JS.

Uh... what? JavaScript is a client-side language (unless you're using NodeJS, which Lemmy is not). Which means JavaScript runs in the browser. And that JavaScript has access to cookies, that's just a basic part of how web browsers work. Lemmy can't do anything to prevent that.

How the attacker got those JWTs? JavaScript sent them to him? Web browser sent them to him when requesting resources form his server? This is lack of site isolation, one web page should not have access to other domains, requesting data form them or sending data to them.

Again, Lemmy can't do anything about that. Once there's a vulnerability that allows an attacker to inject arbitrary JS into the site, Lemmy can't do anything to prevent that JS from making requests.

Then, if they want to administer something, they should log-in using separate username + password into separate log-in form and display completely different web page

On the backend you'd still have a single system which kind of defeats the purpose. Unless you're proposing a completely independent backend? Because that would be a massive PITA to build and would drastically increase the system's complexity and reduce maintainability.

Oh I forgot another line of defense / basic security mitigation. If a server produces an access token (such as JWT or any other old school cookie / session ID), pair it with an IP address. So in case of cookie theft, the attacker cannot use this cookie from his computer (IP address). If the IP changes (mobile / WiFi / ADSL / whatever), the legitimate user should log-in again, now storing two auth cookies. In case of another IP change, no problemo, one of the stored cookies will work. Of course limit validity of the cookie in time (lets, say, keep it valid only for a day or for a week or so).

I'm sure kbin.social blocks lemmygrad, but in case it doesn't: you are such a dork, please learn to not be a dork in the future. Thank you.

And this is why you don’t trust tankies

What are you referring to here?

This is the dumbest possible take about the situation, my lord.

This is a ridiculous take and fairly toxic. Don't ruin any communities with unnecessary hate. It's unwanted.

Tbf, there are far more pressing reasons for distrusting Tankies... Instances getting hacked is for sure aggravating, but it isn't the gulag-backed paranoid ultra-corrupt authoritarian hellhole they so admire and wish to expand globally.