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 SetValue and GetValue functions within the /goform/setDhcpConfig endpoint, which processes the dhcpEn parameter. Improper validation or sanitization of this argument allows an attacker to overflow the stack buffer, potentially overwriting the return address or other control data on the stack. This can lead to arbitrary code execution or cause the device to crash, resulting in denial of service. The vulnerability is remotely exploitable over the network without requiring authentication or user interaction, making it highly dangerous. The CVSS v4.0 score of 8.7 reflects its critical impact on confidentiality, integrity, and availability, with low attack complexity and no privileges required. Although no active exploits have been observed in the wild, the public disclosure of exploit code increases the likelihood of attacks. The vulnerability affects a specific firmware version of the Tenda O3 device, a router commonly used in small to medium enterprise and home networks. Attackers could leverage this flaw to gain control over the router, intercept or manipulate network traffic, or disrupt network services. The lack of an official patch at the time of disclosure necessitates immediate mitigation through network segmentation, access controls, and monitoring.

For European organizations, this vulnerability poses a significant risk to network security and operational continuity. Exploitation could allow attackers to gain unauthorized control over affected routers, enabling interception of sensitive data, manipulation of network traffic, or pivoting to internal networks. This threatens confidentiality and integrity of communications. Additionally, successful exploitation can cause denial of service by crashing the device, impacting availability of critical network infrastructure. Organizations relying on Tenda O3 routers in their network perimeter or internal segments may face increased exposure to cyberattacks, including espionage, ransomware propagation, or disruption of services. The remote and unauthenticated nature of the exploit increases the attack surface, especially for devices exposed to the internet or poorly segmented networks. The public availability of exploit code further elevates the risk, potentially leading to widespread attacks targeting vulnerable devices across Europe.

1. Immediate network-level mitigation: Restrict access to the /goform/setDhcpConfig endpoint by implementing firewall rules or access control lists (ACLs) to block unauthorized external traffic targeting the router's management interface. 2. Network segmentation: Isolate Tenda O3 devices from critical network segments and limit administrative access to trusted internal networks only. 3. Monitoring and detection: Deploy intrusion detection/prevention systems (IDS/IPS) to monitor for suspicious traffic patterns or exploit attempts targeting the vulnerable endpoint. 4. Firmware updates: Monitor Tenda’s official channels for security patches addressing this vulnerability and apply updates promptly once available. 5. Device replacement: For environments where patching is delayed or unavailable, consider replacing affected Tenda O3 routers with devices from vendors with timely security support. 6. Disable unnecessary services: If possible, disable remote management features or services that expose the vulnerable endpoint to reduce attack surface. 7. Incident response readiness: Prepare to respond to potential exploitation attempts by establishing procedures for rapid containment and recovery.