CVE-2026-6135: Tenda F451 Buffer Overflow Vulnerability

CVE-2026-6135 Overview

CVE-2026-6135 is a stack-based buffer overflow vulnerability in the Tenda F451 router running firmware version 1.0.0.7_cn_svn7958. The flaw resides in the fromSetIpBind function within the /goform/SetIpBind endpoint. Attackers can trigger the overflow by manipulating the page argument over the network. Public exploit details are available, increasing the risk of opportunistic attacks against exposed devices. The vulnerability is categorized under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Critical Impact

Remote authenticated attackers can corrupt stack memory on Tenda F451 routers, potentially leading to arbitrary code execution or device crash.

Affected Products

• Tenda F451 router (hardware)
• Tenda F451 Firmware version 1.0.0.7_cn_svn7958
• Devices exposing the /goform/SetIpBind web management endpoint

Discovery Timeline

• 2026-04-13 - CVE-2026-6135 published to NVD
• 2026-04-30 - Last updated in NVD database

Technical Details for CVE-2026-6135

Vulnerability Analysis

The vulnerability exists in the fromSetIpBind handler that processes requests to /goform/SetIpBind on the Tenda F451 router's web management interface. The handler reads the page HTTP parameter and copies it into a fixed-size stack buffer without performing length validation. Sending an oversized page value overflows the buffer and corrupts adjacent stack data, including the saved return address. An attacker with network access to the management interface can use this primitive to crash the device or hijack control flow. The Tenda F451 is a small-business VPN router, so exposed instances directly impact perimeter network availability and trust boundaries.

Root Cause

The root cause is the use of an unbounded string copy operation against attacker-controlled HTTP form data. The fromSetIpBind function does not enforce a maximum length on the page argument before storing it on the stack. This pattern is common across Tenda's httpd/goform request handlers, which traditionally rely on strcpy or sprintf without length checks.

Attack Vector

Exploitation requires network reachability to the router's HTTP management interface and a valid session, since the /goform/SetIpBind endpoint sits behind authentication. An attacker submits a crafted POST request to /goform/SetIpBind with an overlong page parameter. The malformed input triggers the stack overflow inside fromSetIpBind, allowing the attacker to overwrite the saved return address and pivot execution to attacker-controlled data. On MIPS-based Tenda firmware, this typically results in ROP-based payload execution against the device's httpd process.

No verified proof-of-concept code is reproduced here. Technical details are available through the GitHub issue tracker and the VulDB entry #356999.

Detection Methods for CVE-2026-6135

Indicators of Compromise

• HTTP POST requests to /goform/SetIpBind containing abnormally long page parameter values, typically exceeding several hundred bytes.
• Unexpected reboots, httpd crashes, or loss of web management access on Tenda F451 devices.
• Outbound connections from the router to unfamiliar hosts following suspicious management traffic.

Detection Strategies

• Inspect web server and reverse-proxy logs for requests targeting /goform/SetIpBind with non-printable bytes or excessive parameter lengths.
• Deploy network intrusion detection rules that flag oversized form parameters sent to Tenda goform endpoints.
• Correlate router crash telemetry with preceding HTTP administrative requests from non-administrative source addresses.

Monitoring Recommendations

• Restrict and monitor management-plane access by allowlisting administrative source IP addresses.
• Forward router syslog data to a centralized SIEM and alert on repeated httpd restart events.
• Track authentication events on the router's admin interface and investigate logins from unexpected geographies or after hours.

How to Mitigate CVE-2026-6135

Immediate Actions Required

• Remove the Tenda F451 web management interface from any internet-facing interface and confine access to trusted internal networks.
• Rotate administrative credentials on all Tenda F451 devices and disable any shared or default accounts.
• Inventory deployed Tenda F451 routers and identify units running firmware 1.0.0.7_cn_svn7958.

Patch Information

At time of publication, no vendor advisory or fixed firmware release for CVE-2026-6135 has been published on the Tenda official website. Administrators should monitor Tenda's support portal for an updated firmware build addressing the fromSetIpBind overflow and apply it as soon as it becomes available.

Workarounds

• Disable remote web management and require VPN access for any administrative configuration of the device.
• Place affected routers behind an upstream firewall that filters HTTP requests with oversized page parameters to /goform/SetIpBind.
• Where feasible, replace end-of-life or unpatched Tenda F451 units with vendor-supported hardware that receives regular security updates.

# Example upstream firewall rule restricting Tenda F451 admin access to a management subnet
iptables -A FORWARD -p tcp -d <ROUTER_IP> --dport 80 \
  -s 10.10.0.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d <ROUTER_IP> --dport 80 -j DROP