CVE-2025-7758 is a critical buffer overflow vulnerability identified in the TOTOLINK T6 router firmware versions up to 4.1.5cu.748_B20211015. The flaw exists in the HTTP POST request handler, specifically within the setDiagnosisCfg function located in the /cgi-bin/cstecgi.cgi file. The vulnerability arises from improper handling of the 'ip' argument, which can be manipulated by an attacker to cause a buffer overflow. This type of vulnerability can lead to arbitrary code execution, denial of service, or system compromise. The attack vector is remote and does not require user interaction or prior authentication, making it highly exploitable. The CVSS v4.0 score is 8.7 (high severity), reflecting the ease of exploitation (network attack vector, low complexity), no privileges required, and no user interaction needed. The vulnerability impacts confidentiality, integrity, and availability, with a high scope of impact since successful exploitation could allow an attacker to execute arbitrary code with elevated privileges on the device. Although no public exploits are currently known to be in the wild, the disclosure of the exploit code increases the risk of active exploitation in the near future. The TOTOLINK T6 is a consumer and small office/home office (SOHO) router, and such devices are often deployed in various environments, including European households and small businesses.

For European organizations, especially small and medium-sized enterprises (SMEs) and home users relying on TOTOLINK T6 routers, this vulnerability poses a significant risk. Exploitation could lead to unauthorized access to internal networks, interception or manipulation of network traffic, and potential lateral movement to other connected systems. Given the router's role as a gateway device, compromise could undermine network security, leading to data breaches, disruption of business operations, and exposure of sensitive information. The lack of authentication requirement and remote exploitability increases the threat level, as attackers can scan for vulnerable devices and launch attacks without user involvement. In sectors with strict data protection regulations such as GDPR, a breach resulting from this vulnerability could lead to legal and financial repercussions. Additionally, the potential for denial of service could disrupt critical communications and services, impacting business continuity.

1. Immediate firmware update: TOTOLINK users should verify the availability of a patched firmware version from the vendor and apply it promptly. If no patch is currently available, users should monitor vendor communications closely. 2. Network segmentation: Isolate vulnerable TOTOLINK T6 devices from critical network segments to limit potential lateral movement in case of compromise. 3. Access control: Restrict remote management access to the router’s web interface by disabling WAN-side administration or limiting access via firewall rules to trusted IP addresses only. 4. Intrusion detection: Deploy network intrusion detection systems (NIDS) capable of detecting anomalous HTTP POST requests targeting /cgi-bin/cstecgi.cgi or unusual traffic patterns indicative of exploitation attempts. 5. Device replacement: For environments where patching is not feasible or timely, consider replacing affected devices with routers from vendors with robust security update practices. 6. User awareness: Educate users about the risks of using outdated router firmware and encourage regular updates and security hygiene.