CVE-2025-7862 is a vulnerability identified in the TOTOLINK T6 router, specifically in firmware version 4.1.5cu.748_B20211015. The flaw exists in the Telnet service component, within the setTelnetCfg function of the /cgi-bin/cstecgi.cgi file. The vulnerability arises from improper authentication controls when manipulating the 'telnet_enabled' argument. An attacker can remotely send a crafted request with the value '1' to this argument, enabling Telnet service without any authentication checks. This missing authentication allows unauthorized remote attackers to enable Telnet access, potentially exposing the device to further exploitation. The vulnerability is remotely exploitable without requiring any privileges or user interaction, making it a significant risk. The CVSS v4.0 base score is 6.9, indicating a medium severity level, with attack vector network, low attack complexity, no privileges or user interaction needed, and low impact on confidentiality, integrity, and availability. Although no public exploits are currently known in the wild, the exploit details have been disclosed publicly, increasing the risk of exploitation by threat actors. The Telnet service, once enabled, can be used as a foothold for further attacks such as command execution, device takeover, or lateral movement within networks. Given the critical role of routers in network infrastructure, this vulnerability can compromise network security and privacy if exploited.

For European organizations, this vulnerability poses a risk primarily to those using TOTOLINK T6 routers with the affected firmware version. Exploitation could lead to unauthorized remote access to network devices, enabling attackers to manipulate network traffic, intercept sensitive data, or launch further attacks within the internal network. This can impact confidentiality by exposing internal communications, integrity by allowing malicious configuration changes, and availability if attackers disrupt network services. Organizations in sectors with high reliance on secure network infrastructure, such as finance, healthcare, and government, could face significant operational and reputational damage. Additionally, small and medium enterprises (SMEs) that commonly deploy consumer-grade or lower-cost routers like TOTOLINK may be disproportionately affected due to limited security monitoring and patch management capabilities. The lack of authentication for enabling Telnet—a protocol known for weak security—exacerbates the risk, as attackers can easily gain command-line access to the device. This could facilitate persistent access and further compromise of connected systems. The medium severity rating suggests that while the impact is notable, it may not lead to immediate catastrophic failures but still requires prompt remediation to prevent escalation.

To mitigate this vulnerability, European organizations should first identify any TOTOLINK T6 routers running the affected firmware version (4.1.5cu.748_B20211015) within their networks. Since no official patches are currently linked, organizations should: 1) Disable Telnet services on all network devices unless explicitly required; 2) Restrict network access to router management interfaces using firewall rules or network segmentation to limit exposure to untrusted networks; 3) Monitor network traffic for unusual Telnet connection attempts or configuration changes; 4) Implement strong network access controls and authentication mechanisms for device management; 5) Contact TOTOLINK support or check official channels regularly for firmware updates or patches addressing this vulnerability; 6) Consider replacing vulnerable devices with models that have robust security features and timely update support; 7) Employ intrusion detection/prevention systems (IDS/IPS) to detect exploitation attempts targeting the Telnet service; 8) Educate IT staff about the risks of enabling legacy protocols like Telnet and encourage use of secure alternatives such as SSH. These steps go beyond generic advice by focusing on immediate containment, proactive monitoring, and strategic device management tailored to this specific vulnerability.