An issue was discovered on Brother MFC-J491DW C1806180757 devices. The printer's web-interface password hash can be retrieved without authentication, because the response header of any failed login attempt returns an incomplete authorization cookie. The value of the authorization cookie is the MD5 hash of the password in hexadecimal. An attacker can easily derive the true MD5 hash from this, and use offline cracking attacks to obtain administrative access to the device.