CVE-2026-2872 is a stack-based buffer overflow vulnerability identified in the Tenda A21 router firmware version 1.0.0.0. The flaw resides in the set_device_name function within the /goform/setBlackRule endpoint, which is responsible for MAC filtering configuration. Specifically, the vulnerability arises when the devName or mac argument is manipulated, causing the function to write beyond the bounds of a stack buffer. This overflow can corrupt the stack, potentially allowing an attacker to execute arbitrary code remotely. The vulnerability is remotely exploitable without requiring authentication or user interaction, increasing its risk profile. The CVSS 4.0 score of 8.7 reflects its high severity, with network attack vector, low attack complexity, no privileges required, and no user interaction needed. The vulnerability impacts confidentiality, integrity, and availability by enabling attackers to compromise the router, intercept or manipulate network traffic, or disrupt network services. Although no known exploits are currently active in the wild, the public disclosure of the vulnerability increases the likelihood of exploitation attempts. The absence of official patches or mitigation guidance in the provided data suggests that affected users must implement alternative protective measures until a firmware update is available. This vulnerability highlights the critical need for secure coding practices in embedded device firmware, especially for network infrastructure devices like routers.

The exploitation of CVE-2026-2872 can have severe consequences for organizations worldwide. Successful attacks can lead to full compromise of the affected Tenda A21 routers, allowing attackers to execute arbitrary code with system-level privileges. This can result in unauthorized access to internal networks, interception and manipulation of sensitive data, disruption of network services, and potential pivoting to other internal systems. For enterprises, this could mean data breaches, loss of business continuity, and reputational damage. For consumers, compromised routers can be used as part of botnets or for further malicious activities. The vulnerability’s remote exploitability without authentication or user interaction significantly increases the attack surface and risk. Given the critical role routers play in network security and traffic management, this vulnerability threatens the confidentiality, integrity, and availability of network communications. Organizations relying on Tenda A21 devices in their infrastructure must consider this a high-priority risk.

1. Immediate mitigation should focus on network-level protections such as implementing strict firewall rules to restrict access to the router’s management interface, especially blocking access from untrusted external networks. 2. Disable or restrict remote management features on the Tenda A21 router to limit exposure of the vulnerable endpoint. 3. Monitor network traffic for unusual activity that could indicate exploitation attempts targeting the /goform/setBlackRule endpoint. 4. Employ network intrusion detection/prevention systems (IDS/IPS) with signatures or heuristics capable of detecting buffer overflow attempts against this endpoint. 5. Segregate vulnerable routers on isolated network segments to minimize potential lateral movement if compromised. 6. Contact Tenda support or check official channels regularly for firmware updates or patches addressing this vulnerability and apply them promptly once available. 7. As a longer-term measure, consider replacing affected devices with models that have a proven security track record and receive timely security updates. 8. Educate network administrators about this vulnerability and the importance of minimizing exposure of router management interfaces.