Tenda A21 Wi-Fi Stack Buffer Overflow RCE (CVE-2026-2874)

Vendor-confirmed - CVE-2026-2874 is a high remote-code-execution vulnerability in the Tenda A21 Wi-Fi router, firmware version 1.0.0.0, that grants unauthenticated attackers full device compromise via a stack-based buffer overflow. Update your router firmware immediately to mitigate this critical risk.

Overview

A critical security flaw has been identified in the Tenda A21 Wi-Fi router, firmware version 1.0.0.0. This vulnerability allows a remote attacker to send specially crafted network requests to the device, potentially leading to a complete system compromise.

Vulnerability Details

The vulnerability exists in the router’s web management interface, specifically within the function that handles Wi-Fi network name (SSID) changes. Due to insufficient input validation, an attacker can send an overly long network name in a configuration request. This overloads a fixed-size memory buffer on the device’s stack, causing a stack-based buffer overflow. This type of flaw can crash the device (causing a denial of service) or, more critically, allow an attacker to execute arbitrary code on the router.

Impact

The impact of this vulnerability is severe. A remote, unauthenticated attacker could potentially:

• Execute arbitrary code: Gain full control of the router.
• Disrupt network service: Crash the device, causing a widespread internet outage for all connected users.
• Intercept and modify traffic: Redirect internet traffic, steal sensitive data (like login credentials), or deploy malware to devices on the network.
• Pivot to other devices: Use the compromised router as a foothold to attack computers, phones, and other equipment connected to the local network.

The public availability of an exploit increases the risk of active attacks.

Remediation and Mitigation

Primary Action: Firmware Update Immediately check for and install the latest firmware from Tenda’s official support website. As this vulnerability is specific to version 1.0.0.0, an updated version should contain a fix. If no update is available, consider the mitigations below and evaluate replacing the device.

Immediate Mitigations If a firmware patch is not available, take these steps to reduce risk:

1. Disable Remote Management: Ensure the router’s administration interface (often on port 80 or 443) is not accessible from the internet (WAN). It should only be accessible from your local network (LAN).
2. Use a Strong Admin Password: Change the router’s default administrator password to a unique, complex password.
3. Segment Your Network: Place sensitive devices on a separate network segment or VLAN if possible, limiting the attacker’s reach from a compromised router.
4. Monitor for Replacement: Proactively contact Tenda support to inquire about a security patch. If the vendor does not provide a fix, plan to replace the router with a model from a vendor with a strong security update commitment.

Note: Restarting the router does not remediate this flaw. A permanent firmware update or configuration change is required.