ZyXEL Prestige 623, 650, and 652 HW Routers, and possibly other versions, with HTTP Remote Administration enabled, does not require a password to access rpFWUpload.html, which allows remote attackers to reset the router configuration file.
ZynOS 3.40 allows remote attackers to cause a denial of service (link restart) by sending a request for the name \M via the SMB Mail Slot Protocol.