CVE-2025-45866 is a medium-severity buffer overflow vulnerability identified in the TOTOLINK A3002R router, specifically version 4.0.0-B20230531.1404. The vulnerability exists in the formDhcpv6s interface, where improper handling of the addrPoolEnd parameter leads to a buffer overflow condition. Buffer overflow vulnerabilities, classified under CWE-120, 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 data corruption, crashes, or execution of arbitrary code. In this case, the vulnerability does not require user interaction or privileges to exploit (AV:A/AC:L/PR:N/UI:N), indicating that an attacker with network access to the affected interface could exploit it remotely. The CVSS v3.1 score is 5.4 (medium), reflecting limited impact on confidentiality and integrity (both low), and no impact on availability. The attack vector is adjacent network, meaning the attacker must be on the same or a logically adjacent network segment. The vulnerability affects the DHCPv6 server component, which is responsible for assigning IPv6 addresses to clients. Exploiting this flaw could allow an attacker to manipulate DHCPv6 responses or cause denial of service conditions, though no known exploits are currently reported in the wild. The lack of available patches or vendor advisories at this time increases the risk for unmitigated deployments. Given the nature of the vulnerability, exploitation could lead to partial compromise of router operation or leakage of information, but not full system takeover or widespread disruption. The vulnerability was reserved in April 2025 and published in May 2025, indicating recent discovery and disclosure.

For European organizations, this vulnerability poses a moderate risk primarily to network infrastructure relying on TOTOLINK A3002R routers, particularly in environments using IPv6 with DHCPv6 enabled. Successful exploitation could allow attackers on the same network segment (e.g., internal LAN or adjacent wireless networks) to cause service disruptions or potentially manipulate DHCPv6 address assignments, impacting network reliability and security. Confidentiality and integrity impacts are limited but could facilitate further network reconnaissance or targeted attacks. Organizations with critical infrastructure or sensitive data relying on these routers could face operational disruptions or increased exposure to lateral movement by attackers. Since the attack vector requires adjacency, remote exploitation over the internet is unlikely unless the vulnerable interface is exposed. However, in shared or poorly segmented networks, the risk is higher. The absence of known exploits reduces immediate threat but does not eliminate future risk. European entities with IPv6 deployments and TOTOLINK hardware should prioritize assessment and mitigation to prevent exploitation.

1. Network Segmentation: Isolate the DHCPv6 server interface and restrict access to trusted devices only, minimizing the attack surface. 2. Disable DHCPv6 if not required: If IPv6 is not in use, or DHCPv6 services are unnecessary, disable them to eliminate the vulnerable component. 3. Monitor Network Traffic: Implement monitoring for unusual DHCPv6 traffic patterns or malformed packets that could indicate exploitation attempts. 4. Vendor Engagement: Engage with TOTOLINK or authorized distributors to obtain patches or firmware updates addressing this vulnerability as soon as they become available. 5. Access Controls: Restrict administrative and network access to the router interfaces to authorized personnel and devices only. 6. Incident Response Preparedness: Prepare to respond to potential exploitation attempts, including logs collection and forensic readiness. 7. Regular Firmware Updates: Maintain a schedule to update router firmware to the latest versions to reduce exposure to known vulnerabilities. 8. IPv6 Security Best Practices: Employ DHCPv6 guard features, RA guard, and other IPv6-specific security controls to mitigate risks associated with DHCPv6 manipulation.