Junos OS: When a user with the name ftp or anonymous is configured unauthenticated filesystem access is allowed

An Authentication Bypass by Primary Weakness in the FTP server of Juniper Networks Junos OS allows an unauthenticated, network-based attacker to get limited read-write access to files on the device. When the FTP server is enabled and a user named "ftp" or "anonymous" is configured, that user can login without providing the configured password and then has read-write access to their home directory. This issue affects Junos OS:  * all versions before 22.4R3-S8, * 23.2 versions before 23.2R2-S3, * 23.4 versions before 23.4R2.