CVE-2025-8810 is a critical stack-based buffer overflow vulnerability identified in the Tenda AC20 router firmware version 16.03.08.05. The flaw exists in the strcpy function within the /goform/SetFirewallCfg endpoint, specifically triggered by manipulation of the 'firewallEn' argument. Since strcpy does not perform bounds checking, an attacker can supply an overly long input to overflow the stack buffer, potentially overwriting the return address or other control data. This vulnerability is remotely exploitable without authentication or user interaction, as the vulnerable endpoint is accessible over the network. Successful exploitation could allow an attacker to execute arbitrary code with elevated privileges on the device, leading to full compromise of the router. The disclosed exploit code increases the risk of active exploitation, although no confirmed in-the-wild attacks have been reported yet. The CVSS v4.0 base score is 8.7, reflecting high severity due to network attack vector, low attack complexity, no privileges or user interaction required, and high impact on confidentiality, integrity, and availability. The vulnerability affects a widely deployed consumer and small office router model, which is often used as a gateway device in home and small business networks. Given the critical nature of the flaw and the potential for remote code execution, this vulnerability poses a significant security risk to affected deployments.

For European organizations, the impact of CVE-2025-8810 can be substantial. Many small and medium enterprises (SMEs) and home offices rely on consumer-grade routers like the Tenda AC20 due to cost-effectiveness and ease of use. Compromise of these devices can lead to unauthorized network access, interception of sensitive communications, lateral movement within internal networks, and potential deployment of malware or ransomware. Confidentiality is at risk as attackers could intercept or redirect traffic. Integrity and availability could be compromised by attackers modifying firewall settings or disrupting network connectivity. Given the router's role as a network gateway, exploitation could serve as a foothold for further attacks against corporate or personal assets. Additionally, compromised routers can be co-opted into botnets, amplifying threats to broader internet infrastructure. The public disclosure of exploit code increases urgency for European organizations to assess and remediate affected devices to prevent exploitation.

1. Immediate firmware upgrade: Organizations and users should check for and apply any official firmware updates from Tenda addressing this vulnerability. If no patch is available, consider contacting Tenda support for guidance. 2. Network segmentation: Isolate vulnerable routers from critical internal networks to limit potential lateral movement if compromised. 3. Disable remote management: If remote administration features are enabled on the Tenda AC20, disable them to reduce exposure. 4. Implement firewall rules: Block external access to the /goform/SetFirewallCfg endpoint or restrict access to trusted IP addresses only. 5. Monitor network traffic: Deploy intrusion detection/prevention systems (IDS/IPS) to detect anomalous traffic patterns or exploitation attempts targeting the router. 6. Device replacement: For high-risk environments, consider replacing affected routers with models that have a stronger security track record and timely patching. 7. User awareness: Educate users about the risks of using outdated router firmware and encourage regular updates and secure configuration practices. 8. Incident response readiness: Prepare to respond to potential compromises by maintaining backups and having procedures to isolate and remediate infected devices.