CVE-2025-8810 is a critical stack-based buffer overflow vulnerability found in the Tenda AC20 router, specifically in firmware version 16.03.08.05. The vulnerability resides in the strcpy function within the /goform/SetFirewallCfg endpoint, which processes the 'firewallEn' argument. Due to improper input validation, an attacker can supply a crafted input that overflows the stack buffer, potentially overwriting adjacent memory regions. This flaw can be exploited remotely without authentication or user interaction, as the vulnerable function is exposed over the network. The overflow can lead to arbitrary code execution, allowing attackers to take full control of the device, disrupt network traffic, or pivot into internal networks. The CVSS 4.0 score of 8.7 (high severity) reflects the ease of exploitation (network attack vector, low complexity, no privileges or user interaction required) and the significant impact on confidentiality, integrity, and availability. Although no public exploits are currently known in the wild, the vulnerability details have been disclosed, increasing the risk of exploitation by threat actors. The lack of an official patch at the time of publication further exacerbates the risk to affected users. Given the critical role of routers in network infrastructure, successful exploitation could compromise entire organizational networks relying on Tenda AC20 devices.

For European organizations, this vulnerability poses a significant risk to network security and operational continuity. Tenda AC20 routers are commonly used in small to medium enterprises and home office environments due to their cost-effectiveness and feature set. Exploitation could lead to unauthorized access to internal networks, interception or manipulation of sensitive data, and disruption of internet connectivity. This is particularly concerning for sectors handling sensitive personal data under GDPR, such as healthcare, finance, and public administration. Compromise of these routers could facilitate lateral movement within corporate networks, enabling further attacks such as data exfiltration, ransomware deployment, or espionage. Additionally, the widespread use of these devices in residential settings increases the risk of botnet recruitment, which could indirectly affect European organizations through distributed denial-of-service (DDoS) attacks or other malicious activities. The remote and unauthenticated nature of the exploit means that attackers can target vulnerable devices at scale, increasing the potential impact across Europe.

1. Immediate network segmentation: Isolate Tenda AC20 devices from critical internal networks to limit potential lateral movement if compromised. 2. Disable remote management interfaces or restrict access to trusted IP addresses only, reducing the attack surface. 3. Monitor network traffic for unusual activity originating from or targeting Tenda AC20 devices, using IDS/IPS solutions with updated signatures. 4. Implement strict firewall rules to control inbound and outbound traffic on affected devices. 5. Regularly audit and inventory network devices to identify all Tenda AC20 routers and verify firmware versions. 6. Engage with Tenda support channels to obtain or request security patches or firmware updates addressing CVE-2025-8810. 7. If patching is not immediately available, consider replacing vulnerable devices with alternative routers from vendors with timely security support. 8. Educate IT staff on this vulnerability and ensure incident response plans include steps for potential exploitation scenarios involving network infrastructure devices.