CVE-2025-52376 is an authentication bypass vulnerability found in the Nexxt Solutions NCM-X1800 Mesh Router firmware versions UV1.2.7 and below. The flaw exists in the /web/um_open_telnet.cgi endpoint, which allows an attacker to remotely enable the Telnet service without any authentication. Normally, enabling Telnet would require valid credentials or administrative access, but this vulnerability bypasses those security controls entirely. Once Telnet is enabled, the attacker can connect to the router's Telnet server using hard-coded credentials embedded in the firmware. This grants administrative shell access, enabling the execution of arbitrary commands on the device. This level of access effectively compromises the router's confidentiality, integrity, and availability, as the attacker can manipulate configurations, intercept or redirect traffic, install persistent malware, or disrupt network operations. The vulnerability does not require prior authentication or user interaction, making it highly exploitable remotely over the network. Although no known exploits have been reported in the wild yet, the presence of hard-coded credentials combined with an authentication bypass significantly increases the risk of exploitation once the vulnerability becomes publicly known. No official patches or mitigations have been published at the time of disclosure, and the affected firmware versions are not precisely enumerated beyond being UV1.2.7 and below.

For European organizations, this vulnerability poses a significant risk, especially for those relying on Nexxt Solutions NCM-X1800 Mesh Routers in their network infrastructure. Compromise of these routers can lead to unauthorized access to internal networks, interception of sensitive communications, and potential lateral movement to other critical systems. This is particularly concerning for sectors with stringent data protection requirements such as finance, healthcare, and government agencies. The ability to execute arbitrary commands with administrative privileges on network devices can facilitate espionage, data exfiltration, or disruption of services. Additionally, compromised routers can be used as footholds for launching further attacks or as part of botnets. Given the remote exploitability without authentication, attackers can target these devices en masse, increasing the scale and speed of potential attacks. The lack of patches exacerbates the threat, leaving organizations exposed until firmware updates or other mitigations are available.

Organizations should immediately inventory their network devices to identify any Nexxt Solutions NCM-X1800 Mesh Routers running firmware UV1.2.7 or earlier. Until an official patch is released, administrators should disable remote management interfaces, especially Telnet and HTTP access from untrusted networks. Network segmentation should be enforced to isolate vulnerable routers from critical systems and sensitive data. Implement strict firewall rules to block inbound traffic to the /web/um_open_telnet.cgi endpoint and Telnet ports (typically TCP 23). Monitoring network traffic for unusual Telnet activity or unexpected connections to the router can help detect exploitation attempts. If possible, replace affected devices with alternative hardware that does not have this vulnerability. Additionally, change any default or hard-coded credentials on the device, if accessible, to reduce risk. Organizations should maintain close contact with Nexxt Solutions for firmware updates and apply patches promptly once available. Employing intrusion detection systems (IDS) with signatures for this vulnerability can also aid in early detection.