CVE-2026-9389: Tenda F456 Buffer Overflow Vulnerability

CVE-2026-9389 Overview

CVE-2026-9389 is a buffer overflow vulnerability in the Tenda F456 router running firmware version 1.0.0.5. The flaw resides in the frmL7ImForm function within the /goform/L7Im endpoint. Attackers can trigger the overflow by manipulating the page argument over the network. The vulnerability is classified under CWE-119, covering improper restriction of operations within memory buffer bounds. Public disclosure of the exploit increases the risk of opportunistic attacks against exposed devices. Successful exploitation can compromise device confidentiality, integrity, and availability.

Critical Impact

Remote attackers with low privileges can trigger a buffer overflow in the Tenda F456 web interface, potentially leading to memory corruption and arbitrary code execution on affected devices.

Affected Products

• Tenda F456 router, firmware version 1.0.0.5
• Web management interface endpoint /goform/L7Im
• The frmL7ImForm function handling the page parameter

Discovery Timeline

• 2026-05-24 - CVE-2026-9389 published to NVD
• 2026-05-26 - Last updated in NVD database

Technical Details for CVE-2026-9389

Vulnerability Analysis

The vulnerability exists in the frmL7ImForm function, which processes HTTP requests sent to the /goform/L7Im endpoint on the Tenda F456 router. The function fails to validate the length of the page argument before copying it into a fixed-size memory buffer. This improper boundary check enables an attacker to write data past the allocated buffer, corrupting adjacent memory regions. The flaw maps to [CWE-119], improper restriction of operations within the bounds of a memory buffer. According to the EPSS data published on 2026-05-28, the exploitation probability is 0.046% with a percentile of 14.7, but the public availability of proof-of-concept material elevates real-world risk.

Root Cause

The root cause is missing input validation on the page parameter inside frmL7ImForm. The handler copies attacker-controlled data into a stack or heap buffer without enforcing length constraints. This pattern is common in SOHO router firmware that relies on legacy C string handling functions such as strcpy or sprintf without bounds checking.

Attack Vector

An authenticated attacker with low privileges can send a crafted HTTP request to /goform/L7Im over the network. The request includes an oversized page argument designed to overflow the destination buffer. Because the attack surface is network-accessible and attack complexity is low, exploitation is feasible against any reachable device. The publicly disclosed proof of concept is available in the GitHub PoC Repository.

No verified exploit code is reproduced here. Refer to the VulDB Vulnerability Details for additional technical context.

Detection Methods for CVE-2026-9389

Indicators of Compromise

• HTTP POST or GET requests targeting /goform/L7Im with abnormally long page parameter values
• Unexpected reboots, crashes, or process restarts on the Tenda F456 web management daemon
• Outbound connections from the router to unfamiliar IP addresses following suspicious management requests

Detection Strategies

• Inspect web server and router system logs for repeated requests to the /goform/L7Im endpoint originating from external or untrusted networks
• Deploy network intrusion detection signatures that flag HTTP parameters exceeding expected length thresholds on Tenda management interfaces
• Correlate router crash events with preceding HTTP requests to identify exploitation attempts

Monitoring Recommendations

• Enable verbose logging on the router and forward syslog data to a central collector for analysis
• Monitor for unauthenticated or low-privileged access attempts to the management web interface
• Track anomalous traffic patterns from network segments that should not communicate with router administration ports

How to Mitigate CVE-2026-9389

Immediate Actions Required

• Restrict access to the router web management interface to trusted internal networks only
• Disable remote WAN-side administration if it is currently enabled
• Change default and weak credentials on the device to prevent low-privilege attackers from reaching the vulnerable endpoint
• Monitor the Tenda Official Site for firmware updates addressing this vulnerability

Patch Information

As of the last NVD update on 2026-05-26, no official vendor patch has been linked in the CVE record. Administrators should consult the Tenda Official Site for firmware advisories and apply updates as they become available. Until a patch is released, the workarounds below reduce exposure.

Workarounds

• Place affected Tenda F456 devices behind a firewall that blocks unsolicited inbound traffic to management ports
• Segment IoT and consumer-grade networking equipment from sensitive corporate assets
• Where supported, configure ACLs restricting /goform/L7Im access to specific administrative source IP addresses
• Consider replacing end-of-life or unpatched SOHO routers with vendor-supported alternatives

# Example: restrict access to the router management interface using iptables on an upstream gateway
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -s <trusted_admin_subnet> -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -j DROP