CVE-2026-7035: Tenda FH1202 Buffer Overflow Vulnerability

CVE-2026-7035 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda FH1202 wireless router firmware version 1.2.0.14. This vulnerability exists in the fromWrlclientSet function within the /goform/WrlclientSet endpoint of the httpd component. An authenticated remote attacker can exploit this vulnerability by sending a specially crafted request with a manipulated Go argument, potentially leading to arbitrary code execution or denial of service on the affected device.

Critical Impact

Remote attackers with low privileges can exploit this stack-based buffer overflow to potentially gain full control of the affected router, compromising network security and enabling lateral movement within the network.

Affected Products

• Tenda FH1202 Firmware version 1.2.0.14(408)
• Tenda FH1202 Hardware (all revisions running vulnerable firmware)

Discovery Timeline

• 2026-04-26 - CVE-2026-7035 published to NVD
• 2026-04-30 - Last updated in NVD database

Technical Details for CVE-2026-7035

Vulnerability Analysis

This vulnerability is classified as CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The root cause lies in the fromWrlclientSet function's failure to properly validate the length of user-supplied input in the Go parameter before copying it to a fixed-size stack buffer.

When a request is sent to /goform/WrlclientSet, the httpd service processes the Go argument without adequate bounds checking. This allows an attacker to supply an overly long input value that exceeds the allocated buffer size on the stack, potentially overwriting adjacent memory regions including the return address.

The exploit has been publicly disclosed, which increases the urgency for affected organizations to apply mitigations. The network-accessible nature of this vulnerability means that any device exposed to untrusted networks is at heightened risk.

Root Cause

The vulnerability stems from improper input validation in the fromWrlclientSet function. The code fails to verify that the length of the Go parameter does not exceed the size of the destination buffer before performing a copy operation. This classic buffer overflow condition allows attackers to corrupt stack memory, potentially hijacking program execution flow.

Attack Vector

The attack can be launched remotely over the network by an authenticated attacker. The exploitation requires the attacker to send a malicious HTTP request to the /goform/WrlclientSet endpoint with an oversized Go parameter value. When the vulnerable function processes this input, the stack-based buffer overflow occurs, which can lead to:

1. Denial of Service - Crashing the httpd service
2. Remote Code Execution - Overwriting the return address to redirect execution to attacker-controlled code
3. Device Compromise - Gaining persistent access to the router

The vulnerability mechanism involves sending an HTTP POST request to the affected endpoint. When the Go parameter contains data exceeding the expected buffer size, the fromWrlclientSet function copies this data to a stack buffer without bounds checking, resulting in adjacent memory corruption. For detailed technical analysis, refer to the GitHub Vulnerability Repository.

Detection Methods for CVE-2026-7035

Indicators of Compromise

• Unexpected crashes or restarts of the httpd service on Tenda FH1202 devices
• Unusual HTTP POST requests to /goform/WrlclientSet with abnormally large Go parameter values
• Suspicious outbound network connections from the router to unknown external IP addresses
• Configuration changes on the router that were not authorized by administrators

Detection Strategies

• Monitor HTTP traffic to Tenda routers for requests to /goform/WrlclientSet with Go parameters exceeding normal expected lengths
• Implement network intrusion detection rules to flag oversized POST requests to Tenda device management interfaces
• Review web server logs on affected devices for evidence of exploitation attempts
• Deploy network segmentation to isolate IoT and router management interfaces from untrusted networks

Monitoring Recommendations

• Enable logging on network firewalls and proxies to capture traffic destined for router management interfaces
• Configure SIEM alerts for patterns consistent with buffer overflow exploitation attempts against embedded devices
• Regularly audit Tenda device firmware versions against known vulnerable releases
• Monitor for anomalous behavior from network infrastructure devices that may indicate compromise

How to Mitigate CVE-2026-7035

Immediate Actions Required

• Restrict network access to the Tenda FH1202 management interface to trusted IP addresses only
• Disable remote management features if not explicitly required
• Implement firewall rules to block external access to the /goform/ endpoints
• Consider replacing vulnerable devices with supported alternatives if no vendor patch is available

Patch Information

At the time of publication, no official patch from Tenda has been identified in the available references. Organizations should monitor the Tenda Official Website for firmware updates addressing this vulnerability. Additional technical details are available at VulDB #359615.

Workarounds

• Place vulnerable Tenda FH1202 devices behind a firewall that restricts access to management interfaces
• Use access control lists (ACLs) to limit which IP addresses can communicate with the router's web interface
• Disable the httpd web management service if alternative management methods are available
• Implement network segmentation to prevent lateral movement if a device is compromised

# Example: iptables rules to restrict management interface access (apply on upstream firewall)
# Replace 192.168.1.1 with your Tenda router IP and 192.168.1.100 with trusted admin IP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP