CVE-2026-3972: Tenda W3 Buffer Overflow Vulnerability

CVE-2026-3972 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda W3 router firmware version 1.0.0.3(2204). The vulnerability exists in the formSetCfm function within the /goform/setcfm endpoint of the HTTP Handler component. An attacker with adjacent network access can manipulate the funcpara1 argument to trigger a buffer overflow condition, potentially leading to arbitrary code execution or device compromise.

Critical Impact

This vulnerability allows attackers on the local network to exploit a stack-based buffer overflow, potentially gaining complete control over the affected Tenda W3 router. A proof-of-concept exploit has been publicly disclosed.

Affected Products

• Tenda W3 Router Firmware Version 1.0.0.3(2204)

Discovery Timeline

• March 12, 2026 - CVE-2026-3972 published to NVD
• March 12, 2026 - Last updated in NVD database

Technical Details for CVE-2026-3972

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The formSetCfm function in the Tenda W3 router's HTTP Handler fails to properly validate the length of user-supplied input passed through the funcpara1 parameter. When processing requests to the /goform/setcfm endpoint, the function copies the supplied data to a stack buffer without adequate bounds checking.

The attack requires the attacker to be on the same local network (adjacent network access) as the vulnerable device. While this limits the attack surface compared to remotely exploitable vulnerabilities, compromised devices on a home or enterprise network could be leveraged to attack vulnerable Tenda routers. The vulnerability requires no authentication and no user interaction to exploit.

Root Cause

The root cause is insufficient input validation in the formSetCfm function. The HTTP Handler component processes the funcpara1 argument without properly validating its length before copying the data into a fixed-size stack buffer. This allows an attacker to provide an oversized input that overwrites adjacent stack memory, including potentially the return address, enabling control flow hijacking.

Attack Vector

The attack is performed via crafted HTTP requests sent to the /goform/setcfm endpoint on the vulnerable router. An attacker on the local network crafts a malicious request with an oversized funcpara1 parameter value. When the router processes this request, the overflow occurs in the formSetCfm function, allowing the attacker to overwrite stack memory and potentially redirect execution to attacker-controlled code.

The vulnerability mechanism involves sending specially crafted HTTP POST requests to the /goform/setcfm endpoint with an oversized funcpara1 parameter. The formSetCfm function processes this input without proper bounds checking, resulting in a stack buffer overflow. Technical details and proof-of-concept information are available in the GitHub PoC Repository.

Detection Methods for CVE-2026-3972

Indicators of Compromise

• Unusual HTTP POST requests to /goform/setcfm endpoint with abnormally long funcpara1 parameter values
• Router crashes, unexpected reboots, or unresponsive web management interface
• Unexpected network traffic originating from the router to external destinations
• Modified router configurations or firmware without administrator action

Detection Strategies

• Implement network intrusion detection rules to identify HTTP requests with oversized parameters targeting /goform/setcfm
• Monitor router syslog output for crash events or memory corruption indicators
• Use network traffic analysis to detect anomalous patterns from IoT devices including routers
• Deploy SentinelOne Singularity for IoT to identify and protect vulnerable network devices

Monitoring Recommendations

• Enable logging on upstream network devices to capture traffic to/from the router management interface
• Implement network segmentation to isolate IoT devices and monitor cross-segment traffic
• Regularly audit network device firmware versions against known vulnerability databases
• Consider deploying dedicated IoT security monitoring solutions for continuous visibility

How to Mitigate CVE-2026-3972

Immediate Actions Required

• Restrict access to the router's web management interface to trusted hosts only
• Implement network segmentation to isolate the vulnerable router from untrusted network segments
• Monitor the Tenda Official Website for firmware updates addressing this vulnerability
• Consider replacing the device if no patch becomes available

Patch Information

No official patch information is currently available from Tenda. Organizations should monitor the vendor's official channels for security updates. Given the public disclosure of this vulnerability and available proof-of-concept, applying any released patches should be prioritized.

For additional technical details, refer to the VulDB entry tracking this vulnerability.

Workarounds

• Disable remote management access to the router's web interface if not required
• Implement strict access control lists (ACLs) to limit which hosts can communicate with the router's management interface
• Place the router behind a firewall or in a segmented network zone with restricted access
• Consider replacing the affected device with alternative hardware if critical security is required and no patch is available

# Example: Restrict access to router management interface via upstream firewall
# Block external access to router management port (adjust IP and port as needed)
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 443 -j DROP

# Allow only trusted management hosts
iptables -I FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT