CVE-2026-6123: Tenda F451 Buffer Overflow Vulnerability

CVE-2026-6123 Overview

A stack-based buffer overflow vulnerability has been identified in the Tenda F451 router running firmware version 1.0.0.7. The vulnerability exists within the fromAddressNat function in the /goform/addressNat endpoint of the httpd web server component. An attacker can exploit this flaw by manipulating the entrys argument to trigger a buffer overflow condition, potentially leading to remote code execution or denial of service.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability over the network to potentially execute arbitrary code or crash the affected device, compromising network security and availability.

Affected Products

• Tenda F451 Firmware version 1.0.0.7
• Tenda F451 httpd web server component
• /goform/addressNat endpoint with fromAddressNat function

Discovery Timeline

• April 12, 2026 - CVE-2026-6123 published to NVD
• April 13, 2026 - Last updated in NVD database

Technical Details for CVE-2026-6123

Vulnerability Analysis

This vulnerability falls under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), specifically manifesting as a stack-based buffer overflow. The fromAddressNat function within the httpd service fails to properly validate the length of user-supplied input through the entrys parameter before copying it into a fixed-size stack buffer.

The network-accessible nature of this vulnerability allows unauthenticated or low-privileged remote attackers to target the affected endpoint. When exploited, the overflow can overwrite adjacent memory on the stack, including return addresses and saved registers, potentially enabling arbitrary code execution in the context of the httpd process.

The vulnerability has been publicly disclosed, and technical details are available through security research channels, increasing the risk of active exploitation attempts against unpatched devices.

Root Cause

The root cause of this vulnerability is inadequate bounds checking in the fromAddressNat function when processing the entrys argument. The function allocates a fixed-size buffer on the stack but fails to verify that user-supplied data fits within the allocated space before performing memory copy operations. This allows attackers to supply oversized input that overwrites adjacent stack memory, corrupting control flow data structures.

Attack Vector

The attack can be executed remotely over the network by sending a crafted HTTP request to the /goform/addressNat endpoint on the Tenda F451 router. The attacker needs to manipulate the entrys parameter with a payload exceeding the expected buffer size.

The attack flow involves:

1. Identifying a vulnerable Tenda F451 router exposed on the network
2. Crafting an HTTP request to /goform/addressNat with an oversized entrys parameter
3. The malformed input triggers the stack buffer overflow in fromAddressNat
4. Successful exploitation may result in code execution or device crash

Technical details and proof-of-concept information can be found in the GitHub Issue CVE-15 and VulDB Vulnerability #356986.

Detection Methods for CVE-2026-6123

Indicators of Compromise

• Unusual HTTP POST requests to /goform/addressNat with abnormally large entrys parameter values
• Unexpected httpd process crashes or restarts on Tenda F451 devices
• Network traffic containing oversized payloads targeting Tenda router management interfaces
• Evidence of unauthorized configuration changes or suspicious outbound connections from affected devices

Detection Strategies

• Deploy network intrusion detection rules to identify HTTP requests to /goform/addressNat with suspicious payload sizes
• Monitor Tenda router logs for repeated service crashes or abnormal restart patterns in the httpd component
• Implement web application firewall rules to filter requests with excessively long parameter values targeting Tenda management endpoints
• Conduct regular vulnerability scans to identify Tenda F451 devices running firmware version 1.0.0.7

Monitoring Recommendations

• Enable logging for all HTTP requests to router management interfaces and forward logs to a centralized SIEM
• Set up alerts for httpd service failures or unexpected process terminations on Tenda network devices
• Monitor network segments containing vulnerable devices for unusual traffic patterns or scanning activity
• Review device configurations periodically for unauthorized modifications

How to Mitigate CVE-2026-6123

Immediate Actions Required

• Restrict network access to the Tenda F451 web management interface using firewall rules or network segmentation
• Disable remote management features if not required for operations
• Check the Tenda Security Page for available firmware updates addressing this vulnerability
• Implement network monitoring to detect exploitation attempts targeting the vulnerable endpoint

Patch Information

At the time of publication, users should monitor Tenda's official channels for firmware updates that address this vulnerability. The affected firmware version is 1.0.0.7. Organizations should subscribe to security notifications from Tenda and apply patches as soon as they become available. Additional technical details can be found at the VulDB Vulnerability #356986 and related submissions.

Workarounds

• Isolate affected Tenda F451 devices on a separate VLAN with restricted access
• Block external access to port 80/443 on the router's management interface at the network perimeter
• Use a VPN or jump host for administrative access instead of direct exposure to untrusted networks
• Consider replacing affected devices with alternatives that have received security patches if no update is available

# Example: Restrict access to Tenda management interface using iptables
# Only allow management access from trusted admin network
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