CVE-2026-2876 is a stack-based buffer overflow vulnerability identified in the Tenda A18 router firmware version 15.13.07.13. The vulnerability resides in the parse_macfilter_rule function, specifically in the handling of the deviceList parameter submitted via the /goform/setBlackRule endpoint. This endpoint is used to configure MAC address filtering rules on the device. Due to insufficient bounds checking on the deviceList input, an attacker can craft a malicious request that overflows the stack buffer, corrupting adjacent memory. This corruption can lead to arbitrary code execution with the privileges of the router's firmware process, which typically runs with high system privileges. The vulnerability is remotely exploitable over the network without requiring authentication or user interaction, making it highly dangerous. The CVSS v4.0 score of 8.7 reflects the ease of exploitation (network attack vector, low attack complexity), lack of required privileges or user interaction, and the high impact on confidentiality, integrity, and availability. While no known exploits have been observed in the wild, the public disclosure of the vulnerability increases the likelihood of exploitation attempts. The lack of available patches at the time of disclosure means that affected users must rely on interim mitigations until firmware updates are released by Tenda.

The exploitation of CVE-2026-2876 can have severe consequences for organizations and individuals using the Tenda A18 router with the vulnerable firmware. Successful exploitation allows remote attackers to execute arbitrary code on the device with elevated privileges, potentially leading to full device compromise. This can result in unauthorized access to internal networks, interception or manipulation of network traffic, disruption of network services, and the establishment of persistent backdoors. The confidentiality of sensitive data traversing the network can be compromised, integrity of network configurations can be altered, and availability of network connectivity can be disrupted. Given the router's role as a network gateway, the impact extends beyond the device itself to all connected systems. Organizations relying on these routers for critical network infrastructure face increased risk of data breaches, operational disruption, and lateral movement by attackers. The absence of authentication requirements and user interaction for exploitation further elevates the threat level, enabling automated attacks and worm-like propagation within vulnerable environments.

To mitigate the risks posed by CVE-2026-2876, organizations should implement the following specific measures: 1) Immediately restrict remote access to the router's management interface by disabling WAN-side access or limiting it to trusted IP addresses via firewall rules. 2) Employ network segmentation to isolate vulnerable devices from critical infrastructure and sensitive data. 3) Monitor network traffic for unusual or malformed requests targeting the /goform/setBlackRule endpoint, using intrusion detection systems or network monitoring tools. 4) Apply strict input validation and filtering on network gateways where possible to block suspicious payloads attempting to exploit the deviceList parameter. 5) Regularly audit and inventory network devices to identify all instances of Tenda A18 routers running the vulnerable firmware version. 6) Stay informed about firmware updates from Tenda and apply patches promptly once released. 7) Consider deploying alternative network devices with stronger security postures if timely patching is not feasible. 8) Educate network administrators about this vulnerability and the importance of securing router management interfaces. These targeted actions go beyond generic advice by focusing on access control, monitoring, and proactive device management specific to this vulnerability.