CVE-2017-20204
Description
DBLTek GoIP devices (models GoIP 1, 4, 8, 16, and 32) contain an undocumented vendor backdoor in the Telnet administrative interface that allows remote authentication as an undocumented user via a proprietary challenge–response scheme which is fundamentally flawed. Because the challenge response can be computed from the challenge itself, a remote attacker can authenticate without knowledge of a secret and obtain a root shell on the device. This can lead to persistent remote code execution, full device compromise, and arbitrary control of the device and any managed services. The firmware used within these devices was updated in December 2016 to make this vulnerability more complex to exploit. However, it is unknown if DBLTek has taken steps to fully mitigate.
Summary dbcve.org
DBLTek GoIP devices (models 1, 4, 8, 16, and 32) contain an undocumented vendor backdoor in their Telnet administrative interface. The authentication uses a proprietary challenge-response scheme that is fundamentally flawed—the response can be mathematically computed from the challenge alone, allowing remote attackers to authenticate as root without knowing any secret. This grants persistent remote code execution and full device compromise.
Mitigation
Isolate affected devices on restricted network segments with firewall rules blocking external Telnet access, or replace devices if vendor firmware updates are unavailable. Monitor for unauthorized Telnet connections and consider disabling Telnet entirely if not operationally required.