CVE-2026-2886: Tenda A21 Buffer Overflow Vulnerability

CVE-2026-2886 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda A21 router firmware version 1.0.0.0. This critical security flaw affects the set_device_name function within the /goform/SetOnlineDevName file. By manipulating the devName argument, an attacker can trigger a stack-based buffer overflow condition. The vulnerability is remotely exploitable over the network and an exploit has been made publicly available, increasing the risk of active exploitation attempts against affected devices.

Critical Impact

Remote attackers with low privileges can exploit this buffer overflow to potentially achieve code execution on vulnerable Tenda A21 routers, compromising network security and enabling further attacks on connected devices.

Affected Products

• Tenda A21 Firmware version 1.0.0.0
• Tenda A21 Hardware Device
• Network environments utilizing Tenda A21 routers

Discovery Timeline

• 2026-02-21 - CVE-2026-2886 published to NVD
• 2026-02-23 - Last updated in NVD database

Technical Details for CVE-2026-2886

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw exists in the set_device_name function, which processes device name inputs through the /goform/SetOnlineDevName endpoint on Tenda A21 routers.

When a user submits a device name via the devName parameter, the function fails to properly validate the length of the input before copying it to a fixed-size stack buffer. This lack of boundary checking allows an attacker to supply an overly long string that overwrites adjacent memory on the stack, including potentially the return address.

The network-accessible nature of this vulnerability means attackers can craft malicious HTTP requests from any device on the network—or potentially from the internet if the router's management interface is exposed—to trigger the overflow condition.

Root Cause

The root cause of this vulnerability is insufficient input validation in the set_device_name function. The function accepts user-controlled data through the devName parameter without verifying that the input length does not exceed the allocated buffer size on the stack. This classic buffer overflow pattern allows attackers to write beyond the intended memory boundaries, corrupting stack data structures and potentially hijacking program execution flow.

Attack Vector

The attack is conducted remotely over the network. An authenticated attacker with low privileges can send a specially crafted HTTP POST request to the /goform/SetOnlineDevName endpoint containing an oversized devName parameter value. The excessive data overflows the stack buffer, enabling the attacker to potentially:

1. Crash the device (denial of service)
2. Overwrite the return address to redirect execution
3. Execute arbitrary code in the context of the web server process

The vulnerability requires network access to the router's management interface but can be exploited without user interaction once authenticated. For detailed technical analysis, refer to the GitHub Issue Discussion and the VulDB Entry #347180.

Detection Methods for CVE-2026-2886

Indicators of Compromise

• Unexpected router crashes or reboots that may indicate exploitation attempts
• Unusual HTTP POST requests to /goform/SetOnlineDevName with abnormally long devName parameters
• Anomalous network traffic patterns originating from the router's IP address
• Unauthorized configuration changes on the Tenda A21 device

Detection Strategies

• Monitor web server access logs for requests to /goform/SetOnlineDevName with payloads exceeding normal device name lengths
• Implement network intrusion detection rules to identify buffer overflow attack patterns targeting Tenda devices
• Deploy honeypot routers running vulnerable firmware to detect active exploitation campaigns
• Utilize SentinelOne Singularity to detect anomalous process behavior on network segments containing vulnerable IoT devices

Monitoring Recommendations

• Enable logging on network firewalls to capture all traffic to/from Tenda router management interfaces
• Implement alerting for HTTP requests containing unusually large parameter values to router endpoints
• Regularly audit connected device lists and configurations on Tenda A21 routers for unauthorized modifications
• Monitor for firmware update availability from the Tenda Official Website

How to Mitigate CVE-2026-2886

Immediate Actions Required

• Restrict access to the router's web management interface to trusted networks only
• Implement firewall rules to block external access to the router's administrative endpoints
• Disable remote management features if not required for operations
• Consider network segmentation to isolate vulnerable IoT devices from critical infrastructure
• Monitor the Tenda Official Website for firmware security updates

Patch Information

At the time of publication, no official patch has been released by Tenda to address this vulnerability. Administrators should monitor vendor communications and the Tenda Official Website for security updates. Once a patch becomes available, apply it immediately following proper change management procedures.

Additional technical details can be found in the VulDB CTI Information #347180 and the VulDB Submission #754640.

Workarounds

• Configure access control lists (ACLs) to limit management interface access to specific trusted IP addresses only
• Place the Tenda A21 router behind a properly configured firewall that filters malicious requests
• If feasible, replace the vulnerable device with a router from a vendor with a more responsive security update process
• Implement network monitoring to detect and alert on potential exploitation attempts

# Example firewall rule to restrict management access (iptables)
# Block external access to router management interface
iptables -A INPUT -p tcp --dport 80 -s ! 192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s ! 192.168.1.0/24 -j DROP