CVE-2026-3971 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 formwrlSSIDset, located in the /goform/wifiSSIDset endpoint, which handles Wi-Fi SSID configuration requests. Specifically, improper validation and handling of the index/GO argument allows an attacker to supply crafted input that overflows the stack buffer. This overflow can overwrite critical control data on the stack, enabling remote code execution or denial of service. The vulnerability is remotely exploitable over the network without requiring authentication or user interaction, significantly increasing its risk profile. The CVSS 4.0 score of 8.7 reflects its high severity, with low attack complexity, no privileges required, and no user interaction needed. The vulnerability affects the confidentiality, integrity, and availability of the device, potentially allowing attackers to take full control of the router, intercept or manipulate network traffic, or disrupt network services. Although no confirmed exploits in the wild have been reported, the public disclosure of exploit code raises the likelihood of active exploitation attempts. The lack of an official patch at the time of disclosure necessitates immediate mitigation efforts by affected organizations. This vulnerability highlights the critical need for secure input validation in network device firmware, especially for interfaces exposed to remote attackers.

The impact of CVE-2026-3971 on organizations worldwide is significant due to the critical role routers play in network infrastructure. Successful exploitation can lead to complete compromise of the Tenda i3 router, enabling attackers to execute arbitrary code with system-level privileges. This can result in interception and manipulation of all network traffic passing through the device, leading to data breaches, credential theft, and lateral movement within corporate networks. Additionally, attackers could disrupt network availability by causing device crashes or persistent denial of service. The vulnerability's remote and unauthenticated exploitability means attackers can target exposed devices directly over the internet or internal networks without needing prior access. Organizations relying on Tenda i3 routers for home, small office, or branch office connectivity face increased risk of espionage, data loss, and operational disruption. The public availability of exploit code further elevates the threat, increasing the likelihood of automated scanning and exploitation campaigns. Without timely mitigation, this vulnerability could be leveraged by cybercriminals, hacktivists, or nation-state actors to compromise critical network infrastructure.

1. Immediately isolate affected Tenda i3 devices from untrusted networks, especially the internet, to reduce exposure. 2. Disable remote management and administration interfaces on the router to prevent external exploitation attempts. 3. Implement network segmentation to limit the impact of a compromised device and restrict access to critical network segments. 4. Monitor network traffic for unusual patterns or signs of exploitation attempts targeting the /goform/wifiSSIDset endpoint or abnormal SSID configuration requests. 5. Apply any vendor-provided firmware updates or patches as soon as they become available to remediate the vulnerability. 6. If patches are not yet available, consider replacing affected devices with alternative hardware from vendors with timely security updates. 7. Employ intrusion detection/prevention systems (IDS/IPS) with signatures tuned to detect exploitation attempts of this vulnerability. 8. Conduct regular security audits and vulnerability assessments on network infrastructure to identify and remediate similar risks proactively. 9. Educate network administrators on the risks associated with exposed management interfaces and the importance of secure configuration. 10. Maintain an incident response plan to quickly address potential compromises stemming from this vulnerability.