CVE-2026-6135: Tenda F451 Buffer Overflow Vulnerability

CVE-2026-6135 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda F451 routers running firmware version 1.0.0.7_cn_svn7958. This critical security flaw affects the fromSetIpBind function within the /goform/SetIpBind endpoint, where improper handling of the page argument can be exploited to trigger a buffer overflow condition. The attack can be performed remotely over the network, and an exploit has been made publicly available.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially execute arbitrary code, crash the device, or gain unauthorized control over affected Tenda F451 routers. The public availability of exploit code significantly increases the risk of active exploitation.

Affected Products

• Tenda F451 Firmware Version 1.0.0.7_cn_svn7958

Discovery Timeline

• April 13, 2026 - CVE-2026-6135 published to NVD
• April 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6135

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), a fundamental memory safety issue that occurs when software performs operations on a memory buffer without proper bounds checking. In the case of CVE-2026-6135, the fromSetIpBind function fails to properly validate the length of the page argument before copying it to a stack-allocated buffer.

When an attacker sends a crafted HTTP request to the /goform/SetIpBind endpoint with an oversized page parameter, the function copies the malicious input beyond the allocated buffer space on the stack. This overwrites adjacent memory, including potentially critical values such as the saved return address. By carefully crafting the overflow payload, an attacker could redirect program execution to arbitrary code.

Root Cause

The root cause stems from unsafe string handling practices in the firmware's web interface handler. The fromSetIpBind function uses a fixed-size stack buffer to store the page argument without implementing proper length validation. This allows attackers to supply input exceeding the buffer's capacity, resulting in stack memory corruption. The absence of modern memory protection mechanisms in many embedded devices exacerbates the exploitability of this flaw.

Attack Vector

The vulnerability is exploitable over the network without requiring physical access to the device. An attacker can target the router's web management interface by sending a specially crafted HTTP POST request to the /goform/SetIpBind endpoint. The attack requires low-level privileges (authenticated access to the web interface) but no user interaction.

The exploitation workflow typically involves:

1. Gaining access to the router's web management interface (often with default or weak credentials)
2. Sending a POST request to /goform/SetIpBind with an oversized page parameter
3. The overflow corrupts stack memory, potentially allowing control-flow hijacking
4. Attacker-controlled code execution or device crash occurs

For technical details and proof-of-concept information, refer to the GitHub Issue on CVE and VulDB #356999.

Detection Methods for CVE-2026-6135

Indicators of Compromise

• Unusual HTTP POST requests to /goform/SetIpBind with abnormally large page parameter values
• Unexpected router crashes, reboots, or unresponsive behavior following web interface access
• Suspicious network traffic patterns targeting the router's management interface
• Modified router configurations or unauthorized firmware changes

Detection Strategies

• Deploy network intrusion detection systems (IDS) with rules to flag HTTP requests to /goform/SetIpBind containing oversized parameters
• Monitor web server logs on the router (if accessible) for requests with unusually long query strings or POST body parameters
• Implement anomaly detection for router behavior including unexpected reboots or configuration changes
• Use SentinelOne Singularity to monitor network traffic for exploitation attempts targeting IoT devices

Monitoring Recommendations

• Enable logging on perimeter firewalls for all traffic directed at router management interfaces
• Restrict management interface access to trusted internal networks or VPN connections only
• Establish baseline router behavior metrics to detect anomalous crashes or performance degradation
• Consider deploying network-based monitoring solutions that can inspect traffic to embedded devices

How to Mitigate CVE-2026-6135

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management if not required for operations
• Place affected Tenda F451 routers behind a properly configured firewall
• Change default credentials and implement strong authentication for the management interface
• Monitor for firmware updates from Tenda addressing this vulnerability

Patch Information

At the time of publication, no official patch from Tenda has been confirmed for this vulnerability. Administrators should regularly check the Tenda Official Website for firmware updates addressing CVE-2026-6135. Additional vulnerability intelligence can be found at VulDB Submission #792877.

Workarounds

• Implement network segmentation to isolate affected routers from untrusted networks
• Configure firewall rules to block external access to /goform/SetIpBind and other management endpoints
• Deploy a Web Application Firewall (WAF) or reverse proxy with input length validation in front of the management interface
• Consider replacing affected devices with hardware that receives regular security updates
• Use VPN connections for any required remote administration

# Example: Restrict management interface access via iptables
# Block external access to router management port (adjust IP and port as needed)
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP