

Not necessarily. If it’s implemented well, the frontend will just show a “success” message, but the email sent will be different. This way, the owner of the account will know if they already have an account, or if it wasn’t them, that someone else tried to use their email. Meanwhile the bad actor won’t know anything new.




I would be very interested in that book. My university did not provide explicit book sources, so I can’t tell you what that is based on, but here are the relevant slides (from page 9). Server-side hashing is so ubiquitous as the standard that e.g. OWASP cheat sheet doesn’t even explicitly say it, but their recommendations hint at it.
A quick google search on the topic revealed others with the same opinion: stackoverflow stackoverflow. The second link (accepted answer in the same thread) argues that with a protocol around it, it can make sense, but never in the situation described here. There needs to be a meaningful computation on the server’s side, otherwise the described scenario can happen.
It’s a bit difficult to find papers on that because server-side hashing is standard, but here, for example, is a paper that explores client-side hashing (see the introduction with a reference to server-side hashing and section 2): Client Password Hashing paper. Very interesting is also section 3.4. Similar paper: Client-side hashing for efficient typo-tolerant password checkers. Essentially, both suggest that to avoid the described attack, both server-side and client-side hashing is necessary (but the server-side hash can be weaker), see “Authentication attacks after leaks”. Neither paper describes how the client-side hashing is done on the Chinese websites they mention.
You’ll also find that many frameworks (e.g. ASP.NET, Laravel) implement server-side hashing.
My conclusion from the little research I did after your prompt is that client-side hashing can work, but it’s dangerous if done incorrectly (e.g. when done as suggested above), due to the scenario I described.