Avoiding User Enumeration

If an attacker can probe your site to test whether a username exists, it gives them a leg up in trying to hack your users’ accounts.

Risks

Prevalence
Common
Rating prevelance on a298cccc3e525887223509d0e6fe9a464d7d7f60574014de1fe402608154d354 Rating prevelance on a298cccc3e525887223509d0e6fe9a464d7d7f60574014de1fe402608154d354 Rating prevelance on a298cccc3e525887223509d0e6fe9a464d7d7f60574014de1fe402608154d354
Exploitability
Easy
Rating exploitability on 6b817c6c589f0911378579408b6cbfc6d82345849ae2da559b8d11602b9a987b Rating exploitability on 6b817c6c589f0911378579408b6cbfc6d82345849ae2da559b8d11602b9a987b Rating exploitability on 6b817c6c589f0911378579408b6cbfc6d82345849ae2da559b8d11602b9a987b
Impact
Worrying
Rating impact on 48bdb4077813afe9762f27e229e64207ec59c3891a54a3adf931c2c91a6d99bd Rating impact on 48bdb4077813afe9762f27e229e64207ec59c3891a54a3adf931c2c91a6d99bd Rating impact on 48bdb4077813afe9762f27e229e64207ec59c3891a54a3adf931c2c91a6d99bd

Allowing enumeration of usernames is not a vulnerability in itself, but in tandem with other types of vulnerabilities – like the ability to brute-force login – it will compromise the security of your users.