CVE-2026-3803 is a stack-based buffer overflow vulnerability identified in the Tenda i3 router firmware version 1.0.0.6(2204). The flaw exists in the function formWifiMacFilterGet, which is accessible via the /goform/WifiMacFilterGet endpoint. The vulnerability is triggered by manipulating the 'index' parameter, which is improperly validated, leading to a stack buffer overflow condition. This overflow can be exploited remotely without requiring authentication or user interaction, making it highly accessible to attackers. Successful exploitation can result in arbitrary code execution on the device, allowing attackers to gain full control over the router. This can lead to interception or manipulation of network traffic, disruption of network services, or pivoting into internal networks. The CVSS 4.0 base score of 8.7 reflects the high impact on confidentiality, integrity, and availability, combined with low attack complexity and no privileges or user interaction required. Although no active exploitation has been reported, a public exploit is available, increasing the likelihood of future attacks. The vulnerability affects a specific firmware version of the Tenda i3 product line, commonly used in small office and home network environments. The lack of an official patch at the time of disclosure necessitates immediate mitigation efforts to reduce exposure.

The impact of CVE-2026-3803 is significant for organizations using Tenda i3 routers, especially those running the vulnerable firmware version 1.0.0.6(2204). Exploitation can lead to full compromise of the router, enabling attackers to execute arbitrary code remotely. This can result in unauthorized access to internal networks, interception and manipulation of sensitive data, disruption of network availability, and potential lateral movement to other connected systems. For enterprises, this could mean exposure of confidential information, interruption of business operations, and increased risk of further compromise. In environments where Tenda i3 devices serve as critical network gateways, the vulnerability could be leveraged to launch broader attacks or establish persistent footholds. The ease of remote exploitation without authentication amplifies the threat, making it attractive for attackers targeting home users, small businesses, and possibly larger organizations relying on these devices. The availability of a public exploit increases the risk of widespread attacks, potentially leading to botnet recruitment or ransomware deployment. Overall, the vulnerability poses a high risk to network security, data confidentiality, and operational continuity.

To mitigate CVE-2026-3803, organizations should first verify if their Tenda i3 devices are running the affected firmware version 1.0.0.6(2204). If so, they should immediately check for official patches or firmware updates from Tenda and apply them as soon as they become available. In the absence of an official patch, network administrators should restrict access to the management interface, especially blocking external internet access to the /goform/WifiMacFilterGet endpoint. Implementing network segmentation to isolate vulnerable devices from critical infrastructure can limit potential damage. Monitoring network traffic for unusual requests targeting the vulnerable endpoint can help detect exploitation attempts early. Employing intrusion detection/prevention systems (IDS/IPS) with signatures for this vulnerability or the public exploit can provide additional defense. Changing default credentials and disabling unnecessary remote management features reduces attack surface. For home users, replacing vulnerable devices with updated models or alternative vendors may be necessary if patches are not forthcoming. Regularly auditing device firmware versions and maintaining an inventory of network devices will improve preparedness against similar vulnerabilities.