cross-posted from: https://programming.dev/post/10497245
Hi,
For websites I’ve always restricted
usernameto use Apostrophe'and"and some times even space. If a website necessitate special character then I prefer to create an additional DB field ~DisplayName.It’s easier to forbid the use of Apostrophe, otherwise you will have to escape also your search query to match what has been recorded in the DB.
On the topic I’ve this https://security.stackexchange.com/questions/202902/is-single-quote-filtering-nonsense
But if you have better documentation feel free to share :)
Thanks
Nope, don’t place any character restrictions on any field unless it makes sense from an application perspective. Then write tests to ensure the dangerous inputs don’t cause issues.
The only limitations I do is place an upper bound on number of bytes so I don’t get DOSed with an abnormally long field. There are zero length characters, so check based on number of bytes, not UTF codepoints. I set this high enough to not impede users, but low enough to prevent problems (e.g. 256 bytes for username and password) and a separate length limitation for UX purposes (say, 30 characters for user display names).
If you’re limiting characters for security purposes, you’re doing security wrong. Only limit it for application purposes.
That’s great if every external library and application also expects usernames that can contain every character, but mostly they won’t. If you’re very good about testing, you might catch every instance where they don’t, but that doesn’t mean you can necessarily fix them / get them fixed.
Plus, there’s just displaying them. If you have sane limits on usernames, you can have sane user management tools that do things that list users vs. storage used, or whatever. If a username might contain backspace characters or who knows what else, all those tools have to be made more complicated too.
In addition, there’s user support. If you allow usernames to contain zalgo text, you’re going to have far more users needing support because they’re having trouble entering their username. You’re also going to give your support people nightmares trying to help those users out.
“Ok, I see you entered your username as “s̶u̵g̶a̴r̴_̵i̷n̴_̵y̶o̸u̷r̸-̴t̴e̷a̴” not “s̶u̵g̵a̶r̷_̶i̴n̸_̸y̵o̴u̵r̷_̸t̵e̵a̷”, could you try re-entering that username and see if that fixes the problem?”
If your libraries aren’t using proper SQL practices (or any other DB), you should get better libraries. Something like a username should be treated as just bytes by your backend services, so there should never be an issue.
If your frontend wants to limit usernames, that’s fine. But that’s not a security issue, but a display issue.
Why are you imagining this just has to do with SQL? You have a very narrow view of the problem and as a result you’re going to cause yourself massive headaches.
For a username, your backend should only do simple CRUD:
Other than that, you should be using a backend-generated ID, like a UUID or a login token, elsewhere in your application. So for the backend, your only concern related to secure handling of a username is the proper handling of SQL queries for those operations and encoding over the wire. Wire encoding is well defined (URL-encoding or base64), and SQL injection isn’t a thing if you use a decent library correctly. Don’t try to interpret it anywhere, just pass it along as a bunch of bytes, just like a password.
So the only thing left is the frontend, where you should be sanitizing all user input anyway. If the frontend wants to sanitize input in some way, ensure the backend has the same check on creates and updates. But that has nothing to do with backend security, it’s merely a convenience to prevent bugs on the frontend.