CVE-2025-12209 is a stack-based buffer overflow vulnerability identified in the Tenda O3 router firmware version 1.0.0.10(2478). The flaw resides in the handling of the dhcpEn parameter within the SetValue and GetValue functions of the /goform/setDhcpConfig endpoint. An attacker can remotely send crafted requests manipulating this parameter to overflow the stack buffer, potentially overwriting control data such as return addresses. This can lead to arbitrary code execution or cause the device to crash, resulting in denial of service. The vulnerability requires no authentication or user interaction, making it highly exploitable over the network. The CVSS v4.0 score of 8.7 reflects the high impact on confidentiality, integrity, and availability, combined with the ease of remote exploitation. Although no active exploits have been reported in the wild, the public disclosure of exploit code increases the risk of imminent attacks. The affected device, Tenda O3, is a widely used consumer and small business router, often deployed in home and office networks. The lack of an official patch or update at the time of disclosure necessitates immediate mitigation efforts to reduce exposure. Attackers exploiting this vulnerability could gain control over the router, intercept or manipulate network traffic, and pivot to internal networks, posing a significant threat to organizational security.

For European organizations, exploitation of CVE-2025-12209 could lead to severe operational disruptions and data breaches. Compromise of Tenda O3 routers may allow attackers to execute arbitrary code, potentially gaining persistent control over network gateways. This jeopardizes confidentiality by enabling interception or modification of sensitive communications, integrity by altering network configurations or data flows, and availability by causing device crashes or network outages. Small and medium enterprises, as well as home office setups relying on Tenda O3 devices, are particularly vulnerable due to limited security monitoring and patch management capabilities. Critical infrastructure sectors using these routers as part of their network perimeter could face escalated risks, including lateral movement by threat actors. The remote and unauthenticated nature of the exploit increases the attack surface, allowing attackers to target exposed devices over the internet or compromised internal networks. Given the public availability of exploit code, the likelihood of targeted attacks against European entities is elevated, especially in countries with higher Tenda market penetration or geopolitical tensions that motivate cyber espionage or sabotage.

1. Immediately isolate Tenda O3 devices running firmware version 1.0.0.10(2478) from untrusted networks, especially the internet, by disabling remote management interfaces or restricting access via firewall rules. 2. Monitor network traffic for unusual requests to the /goform/setDhcpConfig endpoint, particularly those manipulating the dhcpEn parameter, using intrusion detection systems or custom signatures. 3. Implement network segmentation to limit the impact of a compromised router, ensuring critical systems are not directly reachable through vulnerable devices. 4. Engage with Tenda support or vendor channels to obtain firmware updates or patches addressing this vulnerability; if unavailable, consider replacing affected devices with more secure alternatives. 5. Conduct regular vulnerability scans and penetration tests focusing on network infrastructure to detect exploitation attempts. 6. Educate IT staff on the specific characteristics of this vulnerability to improve incident response readiness. 7. Employ endpoint detection and response tools on connected systems to identify lateral movement or unusual activity stemming from router compromise. 8. If feasible, disable or limit DHCP configuration changes remotely to reduce attack vectors. 9. Maintain up-to-date asset inventories to quickly identify and remediate vulnerable devices across the organization.