CVE-2025-63153 is a stack-based buffer overflow vulnerability identified in the TOTOLink A7000R router firmware version V9.1.0u.6115_B20201022. The vulnerability arises from improper handling of the ssid parameter within the urldecode function, which fails to adequately validate input length or content before processing. An attacker can exploit this by sending a crafted HTTP request containing a maliciously crafted ssid parameter that overflows the stack buffer, leading to memory corruption. The immediate consequence of this overflow is a denial of service (DoS) condition, causing the router to crash or reboot, thereby disrupting network availability. The CVSS v3.1 base score is 7.5, reflecting high severity due to the network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), and impact limited to availability (A:H) without affecting confidentiality or integrity. The vulnerability is classified under CWE-121 (Stack-based Buffer Overflow). Currently, there are no known exploits in the wild and no official patches released by the vendor. However, the vulnerability poses a significant risk to network stability, especially in environments relying on this router model for critical connectivity. Attackers could leverage this flaw to cause repeated outages or disrupt services remotely without authentication, making it a potent denial of service vector.

For European organizations, the primary impact of CVE-2025-63153 is the disruption of network availability due to router crashes induced by the stack overflow. This can lead to temporary loss of internet connectivity, interruption of business operations, and potential cascading effects on dependent services such as VoIP, VPNs, and cloud access. Organizations relying on TOTOLink A7000R routers in their network infrastructure—particularly in small to medium enterprises or branch offices—may experience operational downtime. Critical sectors such as finance, healthcare, and public services could face heightened risks if these routers are part of their network perimeter or internal segmentation. Additionally, repeated exploitation attempts could degrade network performance or require costly incident response and hardware replacement. Although the vulnerability does not expose sensitive data or allow code execution, the denial of service impact alone can have significant operational and reputational consequences.

1. Immediately isolate affected TOTOLink A7000R routers from critical network segments to limit exposure until a patch is available. 2. Implement strict network segmentation and firewall rules to restrict access to router management interfaces and HTTP services, especially blocking unsolicited external traffic targeting the ssid parameter. 3. Deploy intrusion detection/prevention systems (IDS/IPS) with custom signatures to detect and block malformed HTTP requests containing suspicious ssid parameter payloads indicative of exploitation attempts. 4. Monitor router logs and network traffic for anomalies or repeated crashes that may signal exploitation attempts. 5. Engage with TOTOLink support channels to obtain firmware updates or security advisories and apply patches promptly once released. 6. Consider replacing vulnerable devices with alternative models from vendors with stronger security track records if patching is delayed. 7. Educate network administrators on this vulnerability and enforce strict change management to avoid unauthorized configuration changes that could increase risk.