CVE-2026-2874 identifies a stack-based buffer overflow vulnerability in the Tenda A21 router firmware version 1.0.0.0. The vulnerability resides in the function form_fast_setting_wifi_set within the /goform/fast_setting_wifi_set endpoint, which processes the ssid parameter. Improper validation or bounds checking of this input allows an attacker to overflow the stack buffer, potentially overwriting control data such as return addresses. This flaw can be triggered remotely over the network without requiring authentication or user interaction, making it highly exploitable. The buffer overflow could enable an attacker to execute arbitrary code with elevated privileges on the device, leading to full compromise of the router. This could allow attackers to intercept or manipulate network traffic, pivot into internal networks, or disrupt network availability. The vulnerability has a CVSS 4.0 base score of 8.7, reflecting its high impact on confidentiality, integrity, and availability, combined with low attack complexity and no required privileges. Although no active exploitation has been reported, a public exploit has been released, increasing the urgency for mitigation. The lack of official patches at the time of reporting necessitates immediate defensive measures to reduce exposure. The vulnerability affects only version 1.0.0.0 of the Tenda A21 firmware, so verifying firmware versions is critical for risk assessment.

The impact of CVE-2026-2874 is significant for organizations and individuals using Tenda A21 routers running firmware version 1.0.0.0. Successful exploitation can lead to remote code execution, allowing attackers to gain full control over the affected device. This compromises the confidentiality of network traffic, as attackers could intercept or redirect data. Integrity is at risk because attackers can alter router configurations or inject malicious payloads into network communications. Availability may be disrupted through denial-of-service conditions caused by the buffer overflow or subsequent malicious activity. For organizations, compromised routers can serve as footholds for lateral movement into internal networks, risking broader enterprise infrastructure. Consumer and small business users are particularly vulnerable due to limited security monitoring and patch management capabilities. The public availability of an exploit increases the likelihood of attacks, especially from opportunistic threat actors scanning for vulnerable devices. The widespread use of Tenda routers in various regions amplifies the potential scale of impact.

1. Immediately verify if any Tenda A21 devices in your environment are running firmware version 1.0.0.0 and isolate them from critical network segments. 2. Disable remote management interfaces on affected routers to prevent external exploitation of the vulnerable endpoint. 3. Implement network segmentation to limit exposure of vulnerable devices to untrusted networks. 4. Monitor network traffic for unusual requests targeting /goform/fast_setting_wifi_set or suspicious SSID parameter patterns indicative of exploitation attempts. 5. Apply any available firmware updates from Tenda as soon as they are released; if no official patch exists, consider replacing affected devices with models not impacted by this vulnerability. 6. Employ intrusion detection/prevention systems (IDS/IPS) with signatures tuned to detect exploitation attempts of this CVE. 7. Educate users and administrators about the risks and signs of router compromise. 8. Regularly audit router configurations and firmware versions to maintain security hygiene. 9. If possible, restrict access to router management interfaces to trusted IP addresses only. 10. Maintain backups of router configurations to enable rapid recovery if compromise occurs.