CVE-2025-43986 is a critical security vulnerability affecting KuWFi GC111 GC111-GL-LM321_V3.0_20191211 devices. The core issue is that the TELNET service is enabled by default and exposed over the WAN interface without any authentication mechanism. TELNET is an outdated protocol that transmits data, including credentials, in plaintext, making it inherently insecure. Because the service is accessible remotely without authentication, any attacker with network access to the device can connect to the TELNET service and gain full control over the device. This vulnerability allows for complete compromise of confidentiality, integrity, and availability of the affected device. The CVSS v3.1 base score is 9.8 (critical), reflecting the ease of exploitation (no authentication or user interaction required), the network attack vector, and the high impact on all security properties. The vulnerability is categorized under CWE-200 (Exposure of Sensitive Information), indicating that sensitive device information or control is exposed to unauthorized parties. No patches or mitigations have been published yet, and no known exploits are reported in the wild as of the publication date. However, the severity and nature of the vulnerability make it a prime target for attackers once exploit code becomes available. Given that the affected devices are network hardware with WAN exposure, exploitation could lead to device takeover, network pivoting, data interception, or disruption of network services.

For European organizations, this vulnerability poses a significant risk, especially for those using KuWFi GC111 devices in their network infrastructure. Compromise of these devices could lead to unauthorized access to internal networks, interception of sensitive communications, and disruption of critical services. The lack of authentication on a WAN-exposed TELNET service means attackers can remotely execute arbitrary commands, potentially leading to lateral movement within corporate networks. This could result in data breaches, intellectual property theft, or operational downtime. Organizations in sectors such as telecommunications, manufacturing, and critical infrastructure that rely on these devices for connectivity are particularly vulnerable. Additionally, the exposure of these devices on the public internet increases the risk of automated scanning and exploitation by cybercriminal groups or state-sponsored actors. The impact extends beyond the device itself, as compromised network hardware can be used as a foothold for further attacks or as part of botnets for distributed denial-of-service (DDoS) attacks.

Immediate mitigation steps include disabling the TELNET service on all affected KuWFi GC111 devices, especially on WAN interfaces. If disabling TELNET is not feasible, network administrators should restrict access to the TELNET port using firewall rules to allow only trusted internal IP addresses. Implementing network segmentation to isolate these devices from critical network segments can reduce potential impact. Monitoring network traffic for unusual TELNET connections or attempts can help detect exploitation attempts. Since no official patches are currently available, organizations should contact KuWFi for firmware updates or advisories. As a longer-term measure, replacing devices that rely on insecure protocols like TELNET with those supporting secure management protocols such as SSH is recommended. Additionally, organizations should conduct asset inventories to identify all affected devices and ensure they are not exposed to the internet unnecessarily. Employing intrusion detection/prevention systems (IDS/IPS) with signatures for TELNET exploitation attempts can provide additional defense layers.