CVE-2025-45867 is a medium-severity buffer overflow vulnerability identified in the TOTOLINK A3002R router firmware version 4.0.0-B20230531.1404. The flaw exists in the formIpv6Setup interface, specifically through the static_dns1 parameter. Buffer overflow vulnerabilities occur when a program writes more data to a buffer than it can hold, potentially overwriting adjacent memory. This can lead to unpredictable behavior including crashes, data corruption, or arbitrary code execution. In this case, the vulnerability is classified under CWE-121 (Stack-based Buffer Overflow), indicating that the overflow occurs on the stack. The CVSS 3.1 base score is 5.4, reflecting a medium severity level. The vector string CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N indicates that the attack requires adjacent network access (AV:A), has low attack complexity (AC:L), requires no privileges (PR:N) or user interaction (UI:N), and impacts confidentiality and integrity to a limited extent, without affecting availability. No known exploits are currently reported in the wild, and no patches or vendor advisories are available at this time. The vulnerability could allow a remote attacker on the same or adjacent network segment to send specially crafted requests to the router's IPv6 setup interface, causing a buffer overflow that may lead to partial leakage or modification of sensitive data or potentially enable further exploitation depending on the router's internal protections. Given the nature of the device—a consumer or small office router—successful exploitation could compromise network traffic routing or allow attackers to pivot into internal networks.

For European organizations, this vulnerability poses a moderate risk primarily to entities using TOTOLINK A3002R routers or similar devices in their network infrastructure. The impact includes potential unauthorized disclosure or modification of network configuration data, which could degrade network security posture. While the vulnerability does not directly allow denial of service or full system compromise, attackers could leverage it as a foothold for further attacks, such as intercepting or redirecting traffic, or deploying malware within the network. Organizations relying on IPv6 configurations and adjacent network access are particularly at risk. The absence of known exploits reduces immediate risk, but the medium severity score and ease of exploitation without authentication warrant proactive mitigation. In sectors with strict data protection regulations like GDPR, even limited confidentiality breaches could have compliance implications. Additionally, small and medium enterprises (SMEs) using consumer-grade routers without robust security controls may be more vulnerable.

European organizations should first identify any deployment of TOTOLINK A3002R routers, especially version 4.0.0-B20230531.1404, within their network environments. Since no official patches are currently available, immediate mitigation steps include restricting access to the router management interfaces to trusted network segments only, preferably via VLAN segmentation or firewall rules that block access to the formIpv6Setup interface from untrusted or adjacent networks. Disabling IPv6 configuration features if not in use can reduce the attack surface. Network monitoring should be enhanced to detect anomalous traffic patterns targeting router management interfaces. Organizations should also consider replacing vulnerable devices with models from vendors providing timely security updates. Regular firmware update checks are essential once a patch is released. Additionally, applying network segmentation and zero-trust principles can limit lateral movement if exploitation occurs. Finally, maintaining up-to-date asset inventories and vulnerability management processes will help rapidly respond to emerging threats.