Buffer overflow in the Point-to-Point Protocol over Ethernet (PPPoE) module in Huawei USG2100, USG2200, USG5100, and USG5500 unified security gateways with software before V300R001C10SPC600, when CHAP authentication is configured on the server, allows remote attackers to cause a denial of service (server restart) or execute arbitrary code via crafted packets sent during authentication.