CVE-2026-5991: Tenda F451 Buffer Overflow Vulnerability

CVE-2026-5991 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda F451 router firmware version 1.0.0.7. The vulnerability exists within the formWrlExtraSet function located in the /goform/WrlExtraSet endpoint. Improper handling of the GO argument allows an authenticated attacker to trigger a buffer overflow condition, potentially leading to arbitrary code execution or denial of service on affected devices.

Critical Impact

Remote attackers with low-privilege authentication can exploit this stack-based buffer overflow to potentially execute arbitrary code or crash the device, compromising network security.

Affected Products

• Tenda F451 firmware version 1.0.0.7
• Tenda F451 devices with vulnerable /goform/WrlExtraSet endpoint

Discovery Timeline

• 2026-04-10 - CVE-2026-5991 published to NVD
• 2026-04-13 - Last updated in NVD database

Technical Details for CVE-2026-5991

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The vulnerable function formWrlExtraSet fails to properly validate the length of user-supplied input passed through the GO parameter before copying it into a fixed-size stack buffer. When an attacker provides input exceeding the buffer's allocated size, the overflow corrupts adjacent memory on the stack, potentially overwriting return addresses and other critical control data.

The attack can be executed remotely over the network, requiring only low-level authentication to access the vulnerable endpoint. No user interaction is required to trigger the vulnerability once the attacker has authenticated. The exploit methodology has been publicly disclosed, increasing the risk of active exploitation in the wild.

Root Cause

The root cause of CVE-2026-5991 lies in the absence of proper input length validation within the formWrlExtraSet function. When processing HTTP requests to /goform/WrlExtraSet, the function accepts the GO argument without verifying that its length falls within acceptable bounds. This allows attackers to supply oversized input that overflows the stack buffer, demonstrating a classic buffer overflow pattern commonly found in embedded device firmware that lacks memory-safe programming practices.

Attack Vector

The attack vector is network-based, targeting the web management interface of the Tenda F451 router. An attacker must first obtain low-level authentication credentials to access the /goform/WrlExtraSet endpoint. Once authenticated, the attacker crafts a malicious HTTP request containing an oversized value in the GO parameter. The vulnerable formWrlExtraSet function processes this input and copies it to a stack buffer without proper bounds checking, causing the overflow.

The vulnerability can be exploited by sending a specially crafted POST request to the /goform/WrlExtraSet endpoint with a malicious GO parameter value. When the function attempts to process this oversized input, the stack buffer is overflowed, potentially allowing an attacker to overwrite the return address and redirect execution flow. For detailed technical analysis, refer to the GitHub CVE Issue Discussion and the VulDB Vulnerability Report.

Detection Methods for CVE-2026-5991

Indicators of Compromise

• Unusually large HTTP POST requests targeting /goform/WrlExtraSet endpoint
• Malformed or oversized GO parameter values in web server logs
• Unexpected device reboots or crashes following web interface access
• Anomalous outbound network connections from the router device

Detection Strategies

• Monitor HTTP traffic to the router's web management interface for requests to /goform/WrlExtraSet with abnormally large payloads
• Implement network-based intrusion detection rules to flag oversized parameter values in POST requests to Tenda device endpoints
• Deploy endpoint detection on network segments to identify exploitation attempts targeting embedded devices
• Review web server access logs for repeated requests to the vulnerable endpoint with varying payload sizes

Monitoring Recommendations

• Enable logging on the Tenda F451 web interface if available and export logs to a central SIEM
• Configure network monitoring to alert on traffic anomalies to router management interfaces
• Implement segmentation to restrict access to router management interfaces from untrusted networks
• Regularly audit authentication logs for unauthorized access attempts to the device

How to Mitigate CVE-2026-5991

Immediate Actions Required

• Restrict access to the Tenda F451 web management interface to trusted IP addresses only
• Place the router's management interface on a separate VLAN inaccessible from untrusted networks
• Change default credentials and implement strong authentication for the device
• 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. Device owners should regularly check the Tenda Official Website for firmware updates. In the absence of a vendor patch, implementing network-level mitigations and access controls is essential to reduce exposure.

Workarounds

• Disable remote management access to the router if not required for operations
• Implement firewall rules to block external access to the device's web management interface on ports 80 and 443
• Use a VPN to access the router management interface instead of exposing it directly to the network
• Consider replacing affected devices with models that have active security support if no patch is released

# Example: Restrict management interface access using iptables on upstream firewall
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 443 -j DROP
# Allow management access only from trusted admin subnet
iptables -I FORWARD -s <ADMIN_SUBNET> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s <ADMIN_SUBNET> -d <ROUTER_IP> -p tcp --dport 443 -j ACCEPT