MyBooks is anebook management web server also known as Talebook. In 3.41.2 and earlier, the SignUp.post handler for POST /api/user/signup in webserver/handlers/user.py does not enforce the ALLOWREGISTER configuration flag, even though the frontend hides registration controls when the flag is false. An unauthenticated remote attacker can call the endpoint directly and create a valid account on an instance whose administrator disabled public registration. The processauthheader function in webserver/handlers/base.py also does not verify the account's active flag, so the newly created and unactivated account can authenticate immediately and access user-level API functionality. The bypass defeats the intended account-creation policy and can supply the low-privilege account required by related authorization vulnerabilities. This issue is fixed in version 3.42.0.