CVE-2026-2873 is a stack-based buffer overflow vulnerability identified in the Tenda A21 router firmware version 1.0.0.0. The vulnerability resides in the setSchedWifi function, which is accessible via the /goform/openSchedWifi endpoint. By manipulating the schedStartTime or schedEndTime parameters, an attacker can cause a stack overflow, potentially overwriting the return address or other critical stack data. This flaw allows for remote exploitation without requiring authentication or user interaction, making it highly accessible to attackers. The overflow can lead to arbitrary code execution, enabling attackers to gain control over the device, disrupt its operation, or pivot into internal networks. The vulnerability has a CVSS v4.0 base score of 8.7, reflecting its high impact on confidentiality, integrity, and availability. Although no active exploitation has been reported, a public exploit exists, increasing the likelihood of future attacks. The affected product, Tenda A21, is a consumer and small office router, widely used in various regions, which increases the potential attack surface. The lack of available patches at the time of reporting necessitates immediate mitigation efforts to reduce risk.

The impact of CVE-2026-2873 is significant for organizations relying on Tenda A21 routers, particularly in small office and home office environments. Successful exploitation can lead to remote code execution, allowing attackers to take full control of the device. This can result in interception or manipulation of network traffic, unauthorized access to internal resources, and disruption of network availability. The compromise of such routers can serve as a foothold for lateral movement within corporate or residential networks, potentially leading to broader intrusions. Given the router's role as a network gateway, the vulnerability threatens the confidentiality, integrity, and availability of connected systems. The ease of exploitation without authentication or user interaction further elevates the risk, making automated attacks feasible. Organizations without proper network segmentation or monitoring may face increased exposure. The availability of a public exploit increases the urgency to address this vulnerability before widespread exploitation occurs.

1. Immediately restrict remote access to the /goform/openSchedWifi endpoint by implementing firewall rules or access control lists to limit exposure to trusted networks only. 2. Disable remote management features on the Tenda A21 router if not required, reducing the attack surface. 3. Employ network segmentation to isolate vulnerable devices from critical infrastructure and sensitive data. 4. Monitor network traffic for unusual requests targeting the schedStartTime or schedEndTime parameters or the /goform/openSchedWifi endpoint. 5. Apply any available firmware updates or patches from Tenda as soon as they are released. 6. If patches are not yet available, consider temporary device replacement or use of alternative secure routers. 7. Educate users and administrators about the risks and signs of exploitation related to this vulnerability. 8. Implement intrusion detection/prevention systems (IDS/IPS) with signatures targeting this specific exploit once available. 9. Regularly audit router configurations and logs for signs of compromise or attempted exploitation.