Zbtlink L3_V2_8 firmware 3.0.0.4.528, Zbtlink WE826-T2 firmware 19.1101, Zbtlink ZBT-7628 firmware 1.0.0.2.007, Zbtlink ZBT-ZBT7621 firmware 1.0.0.3.001, MoreQuick MQAC-7620, MQAC-7620A, MQAP-7620, MQAP-7620A, and MQAP-7628 firmware 1.0.0.2.000, AP522 firmware 1.0.0.2.014, AP7628 and HC5661A firmware 3.0.0.4.380, APG721B firmware 19.0809, HK300 firmware 1.0.0.2.032, and MAP-N10 firmware 1.0.0.2.044 ship a backdoor command-and-control implant (yunmgrd) reachable over an unauthenticated cleartext UDP channel to a hardcoded C2 server. A remote unauthenticated attacker on the network path can hijack the channel and execute arbitrary commands as root. The attacker can also modify DNS entries, exfiltrate PPPoE credentials, and open reverse SSH tunnels.

Multiple Zbtlink and MoreQuick router firmware versions ship with a pre-installed backdoor C2 implant called 'yunmgrd' that communicates over an unauthenticated cleartext UDP channel to a hardcoded C2 server. A remote unauthenticated attacker on the network path can hijack this channel and execute arbitrary commands as root on affected devices. The vulnerability affects a wide range of devices including Zbtlink L3_V2_8, WE826-T2, ZBT-7628, ZBT-ZBT7621, MoreQuick MQAC/MQAP series, AP522, AP7628, HC5661A, APG721B, HK300, and MAP-N10. Beyond remote code execution, the attacker can modify DNS entries, exfiltrate PPPoE credentials, and establish reverse SSH tunnels for persistent access. This is effectively a supply-chain-level backdoor shipped in production firmware, posing severe risks to network infrastructure and connected environments. The issue was reported by VulnCheck under the campaign name 'DarkLantern/SpeakingStone'.