CVE-2026-3973: Tenda W3 Buffer Overflow Vulnerability

CVE-2026-3973 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda W3 router firmware version 1.0.0.3(2204). The vulnerability exists within the formSetAutoPing function located in the /goform/setAutoPing endpoint of the POST Parameter Handler component. By manipulating the ping1 or ping2 arguments, an attacker can trigger a stack-based buffer overflow condition. This vulnerability can be exploited remotely over the network, and proof-of-concept exploit code has been publicly disclosed.

Critical Impact

Remote attackers with low privileges can exploit this buffer overflow vulnerability to potentially achieve code execution on affected Tenda W3 routers, compromising network infrastructure and enabling further lateral movement within the network.

Affected Products

• Tenda W3 Firmware Version 1.0.0.3(2204)

Discovery Timeline

• March 12, 2026 - CVE-2026-3973 published to NVD
• March 12, 2026 - Last updated in NVD database

Technical Details for CVE-2026-3973

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The formSetAutoPing function in Tenda W3 routers fails to properly validate the length of user-supplied input for the ping1 and ping2 POST parameters before copying them to a fixed-size stack buffer.

The vulnerability allows a network-based attacker with low-level authentication to send specially crafted POST requests to the /goform/setAutoPing endpoint. When the ping1 or ping2 parameter contains data exceeding the expected buffer size, the overflow occurs on the stack, potentially overwriting critical memory regions including the return address and saved registers.

The attack can be executed remotely without any user interaction, making it particularly dangerous for exposed router management interfaces. Successful exploitation could lead to denial of service through process crashes, or potentially remote code execution if the attacker can control the overwritten memory to redirect program flow.

Root Cause

The root cause of this vulnerability is insufficient bounds checking on user-controlled input within the formSetAutoPing function. The code processes the ping1 and ping2 POST parameters without validating their length against the destination buffer capacity. This classic buffer overflow condition allows attackers to write beyond the allocated stack buffer boundaries, corrupting adjacent memory and potentially hijacking execution flow.

The lack of proper input sanitization in embedded device firmware is a common issue, particularly when dealing with web-based management interfaces that handle user input directly in memory-constrained environments.

Attack Vector

The attack vector is network-based, requiring no user interaction to exploit. An attacker can send malicious HTTP POST requests to the vulnerable /goform/setAutoPing endpoint on the Tenda W3 router's management interface. The attack requires low-level authentication privileges to access the vulnerable function.

The exploitation process involves sending an oversized string in either the ping1 or ping2 POST parameter. When the vulnerable function processes this input, the stack buffer is overflowed, potentially allowing the attacker to:

1. Crash the web service or entire router (Denial of Service)
2. Overwrite return addresses to redirect execution flow
3. Execute arbitrary code in the context of the router's embedded system

Proof-of-concept exploits have been publicly disclosed for both vulnerable parameters. For detailed technical information, refer to the ping1 buffer overflow PoC and ping2 buffer overflow PoC repositories.

Detection Methods for CVE-2026-3973

Indicators of Compromise

• Unusual or repeated HTTP POST requests to /goform/setAutoPing endpoint with abnormally long parameter values
• Router crashes or unexpected reboots coinciding with external access attempts to the management interface
• Memory corruption errors or segmentation faults in router system logs
• Unauthorized configuration changes or new user accounts on the router

Detection Strategies

• Deploy network intrusion detection rules to identify HTTP POST requests to /goform/setAutoPing with oversized ping1 or ping2 parameters exceeding normal operational values
• Monitor for anomalous traffic patterns targeting router management interfaces on internal networks
• Implement web application firewall (WAF) rules to block requests with payload sizes exceeding expected thresholds for router configuration endpoints
• Review access logs for repeated failed or malformed requests to the vulnerable endpoint

Monitoring Recommendations

• Enable comprehensive logging on Tenda W3 router management interfaces and centralize logs for analysis
• Configure network monitoring to alert on direct access attempts to router management ports from untrusted networks
• Establish baseline traffic patterns for legitimate management interface usage to detect anomalies
• Monitor for signs of router compromise such as unexpected outbound connections or DNS configuration changes

How to Mitigate CVE-2026-3973

Immediate Actions Required

• Restrict access to the Tenda W3 router management interface to trusted IP addresses only using firewall rules
• Disable remote management access if not required for operations
• Segment network infrastructure to isolate router management interfaces from general user traffic
• Monitor for exploitation attempts using network intrusion detection systems

Patch Information

As of the last NVD update on March 12, 2026, no official patch has been released by Tenda. Users should monitor the Tenda Official Website for firmware updates addressing this vulnerability. Consider replacing affected devices with alternative hardware if patches are not made available in a timely manner, given the public availability of exploit code.

For additional vulnerability details and tracking, consult the VulDB entry #350408.

Workarounds

• Implement network-level access controls to restrict management interface access to specific trusted IP addresses or VPN-only access
• Deploy a reverse proxy or web application firewall in front of the management interface to filter oversized POST parameters
• Disable the auto-ping functionality if it is not required for router operations
• Consider network segmentation to place router management interfaces on isolated management VLANs inaccessible from general network traffic

# Example firewall configuration to restrict management interface access
# Allow management access only from trusted admin workstation
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP

# Block external access to router management interface
iptables -A INPUT -p tcp --dport 80 -i wan0 -j DROP