CVE-2026-2876 identifies a critical stack-based buffer overflow vulnerability in the Tenda A18 router firmware version 15.13.07.13. The vulnerability resides in the parse_macfilter_rule function, which processes the deviceList parameter submitted to the /goform/setBlackRule endpoint. Improper input validation or bounds checking allows an attacker to supply a crafted deviceList argument that overflows the stack buffer. This overflow can corrupt the stack frame, potentially enabling arbitrary code execution or denial of service. The attack vector is remote network access to the vulnerable endpoint, requiring no authentication or user interaction, which significantly lowers the barrier to exploitation. The vulnerability has a CVSS 4.0 base score of 8.7, reflecting its high impact on confidentiality, integrity, and availability, as well as ease of exploitation. While no public exploits have been observed in the wild, the public disclosure increases the likelihood of future exploitation attempts. The affected product, Tenda A18, is a consumer-grade wireless router widely used in various regions, making this vulnerability relevant for both home users and small businesses relying on this hardware for network connectivity and security.

The exploitation of CVE-2026-2876 can have severe consequences for affected organizations and individuals. Successful exploitation may allow attackers to execute arbitrary code with elevated privileges on the router, leading to full device compromise. This can result in unauthorized network access, interception or manipulation of network traffic, disruption of internet connectivity, and potential pivoting to internal networks for further attacks. The integrity and confidentiality of data passing through the router can be compromised, and availability may be affected due to device crashes or reboots triggered by the overflow. Given the router’s role as a network gateway, the impact extends beyond the device itself to all connected systems. Organizations using Tenda A18 routers without mitigation or firmware updates are at risk of targeted attacks, especially in environments where these devices are exposed to untrusted networks or the internet.

To mitigate CVE-2026-2876, organizations should immediately verify if their Tenda A18 routers are running firmware version 15.13.07.13 and restrict access to the /goform/setBlackRule endpoint from untrusted networks. Network segmentation and firewall rules should be implemented to block external access to router management interfaces. If possible, disable remote management features or restrict them to trusted IP addresses. Monitor network traffic for unusual requests targeting the deviceList parameter or the /goform/setBlackRule endpoint. Since no official patch is currently available, consider upgrading to a newer firmware version once released by Tenda that addresses this vulnerability. As a temporary measure, replace affected devices with alternative hardware from vendors with timely security updates. Additionally, implement network intrusion detection systems (NIDS) to detect exploitation attempts and maintain regular backups of router configurations to facilitate recovery.