This vulnerability is due to hidden functionality in the /goform/setSysTools endpoint of Nexxt Solutions Nebula 300+ firmware through version 12.01.01.37. An authenticated attacker can send a crafted POST request including parameters such as telnetManageEn=true and telnetPwd to activate a Telnet service on port 23. The CVSS 4.0 score is 8.5, indicating high severity, with attack vector being adjacent network, low attack complexity, no user interaction, and requiring high privileges. The vulnerability is classified under CWE-912 (Hidden Functionality).

An authenticated attacker with high privileges can enable Telnet service remotely, potentially increasing the attack surface of the device by exposing it to Telnet-based attacks. This could lead to unauthorized access or further compromise if Telnet credentials are weak or reused. However, exploitation requires authentication and high privileges, limiting the scope to already partially trusted users.

No official patch or fix is currently documented. Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, restrict access to the device management interface to trusted administrators only and monitor for unauthorized Telnet activation. Disable Telnet service if it is not required or possible to do so manually.