CVE-2025-6402 is a critical buffer overflow vulnerability identified in the TOTOLINK X15 router, specifically in version 1.0.0-B20230714.1105. The flaw exists within the HTTP POST request handler component, targeting the /boafrm/formIpv6Setup endpoint. The vulnerability arises from improper handling of the 'submit-url' argument, which can be manipulated by an attacker to cause a buffer overflow condition. 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 4.0 base score is 8.7 (high severity), reflecting the ease of exploitation (network attack vector, low attack complexity), no privileges required, and no user interaction needed. The impact metrics indicate high confidentiality, integrity, and availability impacts, meaning successful exploitation could allow an attacker to fully control the device or disrupt its operation. Although no official patch links are currently available and no known exploits have been observed in the wild, the public disclosure of the exploit code increases the risk of imminent attacks. The TOTOLINK X15 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. The vulnerability's presence in the IPv6 setup handler suggests that networks using IPv6 configurations on this device are particularly at risk. Given the critical nature of the flaw and the remote, unauthenticated attack vector, this vulnerability represents a significant threat to affected devices until mitigated.

For European organizations, especially small and medium enterprises (SMEs) and residential users relying on TOTOLINK X15 routers, this vulnerability poses a serious risk. Exploitation could lead to full compromise of the router, allowing attackers to intercept, modify, or redirect network traffic, potentially leading to data breaches, espionage, or disruption of business operations. The compromise of network infrastructure devices like routers can serve as a foothold for lateral movement within corporate networks or as a launchpad for further attacks such as man-in-the-middle (MITM) or ransomware campaigns. Given the increasing adoption of IPv6 in Europe, the vulnerability in the IPv6 setup handler increases the attack surface. Additionally, the lack of authentication and user interaction requirements means attackers can exploit this vulnerability at scale, potentially affecting large numbers of devices. The absence of patches and the public availability of exploit code further exacerbate the threat, increasing the likelihood of exploitation. Critical infrastructure and organizations with remote or distributed workforces using these routers may face elevated risks of network compromise and data loss.

Immediately identify and inventory all TOTOLINK X15 devices running version 1.0.0-B20230714.1105 within the network environment. Isolate affected devices from critical network segments to limit potential lateral movement if compromise occurs. Disable remote management and HTTP access to the router’s administrative interface, especially from untrusted networks. If feasible, disable IPv6 configuration or the specific /boafrm/formIpv6Setup functionality until a vendor patch is released. Monitor network traffic for unusual patterns indicative of exploitation attempts, such as unexpected POST requests to /boafrm/formIpv6Setup. Implement network-level protections such as Web Application Firewalls (WAFs) or Intrusion Prevention Systems (IPS) with custom rules to detect and block malformed HTTP POST requests targeting this endpoint. Engage with TOTOLINK support channels to obtain or request security patches or firmware updates addressing this vulnerability. Educate users and administrators about the risk and signs of router compromise, including unexpected device behavior or network anomalies. Plan for rapid deployment of firmware updates once available and consider replacement of affected devices if no patch is forthcoming. Regularly back up router configurations and maintain an incident response plan tailored to network infrastructure compromise.