CVE-2026-3803 identifies a critical stack-based buffer overflow vulnerability in the Tenda i3 router firmware version 1.0.0.6(2204). The vulnerability resides in the function formWifiMacFilterGet, specifically in the handling of the 'index' parameter passed to the /goform/WifiMacFilterGet endpoint. Improper validation or bounds checking of this argument allows an attacker to overwrite the stack memory, leading to a buffer overflow condition. This flaw can be triggered remotely over the network without requiring authentication or user interaction, making it highly exploitable. Successful exploitation could allow attackers to execute arbitrary code with elevated privileges on the device, potentially leading to full device compromise. The vulnerability has a CVSS 4.0 base score of 8.7, reflecting its high severity due to network attack vector, low attack complexity, no privileges or user interaction required, and high impact on confidentiality, integrity, and availability. Although no confirmed active exploitation has been reported, a public exploit is available, increasing the urgency for mitigation. The vulnerability affects a widely deployed consumer and small office router model, which often serves as a gateway device, amplifying the potential impact on connected networks. No official patches or updates have been linked yet, highlighting the need for interim mitigations.

The impact of CVE-2026-3803 is significant for organizations and individuals using the Tenda i3 router model 1.0.0.6(2204). Exploitation can lead to arbitrary code execution on the device, allowing attackers to take full control of the router. This control can be leveraged to intercept, manipulate, or disrupt network traffic, compromise connected devices, and establish persistent footholds within networks. The confidentiality of sensitive data passing through the router can be breached, integrity of network communications can be undermined, and availability of network services can be disrupted or denied. For enterprises and critical infrastructure relying on these routers, this vulnerability poses a risk of lateral movement, data exfiltration, and network outages. The ease of remote exploitation without authentication increases the likelihood of widespread attacks, especially given the availability of public exploits. The absence of patches further exacerbates the risk, potentially leading to targeted attacks or automated scanning and exploitation campaigns.

Given the absence of an official patch, organizations should implement several specific mitigations: 1) Immediately isolate affected Tenda i3 routers from untrusted networks, especially the internet, to reduce exposure. 2) Disable or restrict access to the /goform/WifiMacFilterGet endpoint if possible, using router configuration or firewall rules to block malicious requests targeting the vulnerable function. 3) Employ network segmentation to limit the impact of a compromised router on critical internal systems. 4) Monitor network traffic for unusual patterns indicative of exploitation attempts, such as anomalous requests to the vulnerable endpoint or unexpected device behavior. 5) Consider replacing affected devices with models from vendors with active security support and patch management. 6) Regularly update router firmware when official patches become available and subscribe to vendor security advisories. 7) Use intrusion detection/prevention systems (IDS/IPS) with signatures targeting this vulnerability to detect and block exploitation attempts. 8) Educate network administrators about the vulnerability and encourage prompt incident response readiness.