Tenda A21 stack overflow lets attackers crash

Vendor-confirmed - CVE-2026-2871 is a high remote code execution in Tenda A21 router version 1.0.0.0 that grants an unauthenticated attacker full control of the device via a stack buffer overflow. A public exploit increases urgency; update immediately.

Overview

A critical security flaw has been identified in the Tenda A21 Wi-Fi router (version 1.0.0.0). The vulnerability is a remote stack-based buffer overflow within the device’s web management interface. This allows an attacker to send specially crafted network requests to the router, potentially leading to a complete system compromise.

Vulnerability Details

The flaw resides in the fromSetIpMacBind function, which handles IP and MAC address binding rules. This function does not properly validate the length of input data it receives. By sending an overly long argument list to the /goform/SetIpMacBind page, an attacker can overflow a buffer in the device’s memory. This type of corruption can crash the device or, more critically, allow the attacker to execute arbitrary code. The exploit for this vulnerability is publicly available, increasing the risk of active attacks.

Potential Impact

If successfully exploited, this vulnerability can have severe consequences:

• Remote Code Execution: An unauthenticated attacker on the same network could gain full control of the router.
• Denial of Service: The router could be crashed, causing a complete loss of internet connectivity for all connected devices.
• Network Compromise: A compromised router can be used to intercept or redirect traffic, steal sensitive information, and launch further attacks against other devices on the local network.

Remediation and Mitigation

Immediate action is required to protect affected networks.

Primary Solution - Firmware Update:

1. Check the official Tenda support website for a firmware update that addresses CVE-2026-2871.
2. If an update is available, install it immediately following the vendor’s instructions.
3. If no patch is available, contact Tenda support to inquire about a timeline for a fix.

Interim Mitigations:

• Restrict Access: If possible, disable remote administration (WAN access) to the router’s management interface. Ensure the admin panel is only accessible from your local area network (LAN).
• Network Segmentation: Place the router on a dedicated network segment, limiting its exposure to untrusted devices.
• Monitor for Replacement: Given the public availability of an exploit and the high severity, consider replacing the device with a model from a vendor that provides regular security updates if a patch is not promptly released.

General Best Practice: Always change the router’s default administrator password and disable any unused management services.