US-CERT has issued a Vulnerability Note (VU#950576) for some DSL routers, excerpted below, see US-CERT note for full details:
DSL routers contain hard-coded “XXXXairocon” credentials
DSL routers by ASUS, DIGICOM, Observa Telecom, Philippine Long Distance Telephone (PLDT), and ZTE contain hard-coded “XXXXairocon” credentials
CWE-798: Use of Hard-coded Credentials
DSL routers, including the ASUS DSL-N12E, DIGICOM DG-5524T, Observa Telecom RTA01N, Philippine Long Distance Telephone (PLDT) SpeedSurf 504AN, and ZTE ZXV10 W300 contain hard-coded credentials that are useable in the telnet service on the device. In the ASUS, DIGICOM, Observa Telecom, and ZTE devices, the username is “admin,” in the PLDT device, the user name is “adminpldt,” and in all affected devices, the password is “XXXXairocon” where “XXXX” is the last four characters of the device’s MAC address. The MAC address may be obtainable over SNMP with community string public. The vulnerability was previously disclosed in VU#228886 and assigned CVE-2014-0329 for ZTE ZXV10 W300, but it was not known at the time that the same vulnerability affected products published by other vendors. The Observa Telecom RTA01N was previously disclosed on the Full Disclosure mailing list.
Impact: A remote attacker may utilize these credentials to gain administrator access to the device.
Solution: The CERT/CC is currently unaware of a practical solution to this problem and recommends the following workaround: Restrict access: Enable firewall rules so the telnet service of the device is not accessible to untrusted sources. Enable firewall rules that block SNMP on the device.
Vendors impacted include: AsusTek, DIGICOM, Observa Telecom, Philippine Long Distance Telephone, and ZTE Corporation.
See CERT VU for full information: