CVE-2026-6121: Tenda F451 Buffer Overflow Vulnerability

CVE-2026-6121 Overview

CVE-2026-6121 is a stack-based buffer overflow vulnerability in the Tenda F451 router running firmware version 1.0.0.7. The flaw resides in the WrlclientSet function of the /goform/WrlclientSet endpoint within the httpd component. An attacker can trigger the overflow by manipulating the GO argument submitted to the web interface. The attack can be initiated remotely over the network and requires only low-level privileges. The exploit has been publicly disclosed, increasing the risk of opportunistic exploitation against exposed devices.

Critical Impact

Remote attackers with low privileges can corrupt stack memory in the router's httpd process, potentially leading to arbitrary code execution or device crashes.

Affected Products

• Tenda F451 router (hardware)
• Tenda F451 firmware version 1.0.0.7
• Web management interface httpd component

Discovery Timeline

• 2026-04-12 - CVE-2026-6121 published to NVD
• 2026-04-29 - Last updated in NVD database

Technical Details for CVE-2026-6121

Vulnerability Analysis

The vulnerability is classified under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer). It affects the WrlclientSet handler exposed through the Tenda F451 web administration interface. The handler processes wireless client configuration requests submitted to /goform/WrlclientSet. When the GO parameter is supplied, the function copies attacker-controlled data onto a fixed-size stack buffer without verifying the input length. This unchecked copy allows the adjacent stack frame, including saved return addresses, to be overwritten.

Successful exploitation can corrupt control-flow data in the httpd process. Because Tenda small office and home office (SOHO) routers commonly run services as root and lack hardening such as Address Space Layout Randomization (ASLR), overflow conditions on these devices frequently translate into reliable code execution. At minimum, the overflow crashes the web server and disrupts management of the device.

Root Cause

The root cause is missing bounds validation on the GO HTTP parameter before it is written into a stack-allocated buffer inside WrlclientSet. The function trusts the request length as supplied by the client and uses an unsafe copy routine. Standard length checks and use of bounded string-handling functions would have prevented the overflow.

Attack Vector

The attack vector is network-based. An attacker sends a crafted HTTP request to /goform/WrlclientSet containing an oversized value for the GO argument. Authentication to the router web interface is required, which limits exploitation to attackers who have valid credentials, who have obtained credentials through default-password reuse, or who have access to the LAN side of the device. No verified proof-of-concept code is referenced in the NVD entry; technical details are tracked in the GitHub Issue #12 and VulDB #356984 advisories.

Detection Methods for CVE-2026-6121

Indicators of Compromise

• Unexpected restarts or crashes of the httpd process on Tenda F451 devices
• HTTP POST requests to /goform/WrlclientSet containing abnormally long GO parameter values
• Loss of management plane access immediately following a request to the WrlclientSet endpoint
• Outbound connections from the router to unfamiliar IP addresses after a suspicious management request

Detection Strategies

• Inspect web access logs and network flow data for requests targeting /goform/WrlclientSet with parameter lengths exceeding expected sizes
• Deploy intrusion detection signatures that flag oversized GO parameter values directed at Tenda management interfaces
• Correlate router availability monitoring alerts with recent administrative HTTP activity to identify exploitation attempts

Monitoring Recommendations

• Restrict and log all access to the router administrative interface from both LAN and WAN segments
• Forward syslog from network devices to a centralized analytics platform for retention and correlation
• Monitor for new or unauthorized configuration changes to wireless client settings on F451 devices

How to Mitigate CVE-2026-6121

Immediate Actions Required

• Disable remote (WAN-side) administration on Tenda F451 devices until a patch is available
• Restrict LAN access to the management interface to a dedicated administrative network or trusted hosts
• Rotate administrative credentials and remove default or shared accounts that could enable authenticated exploitation
• Inventory all Tenda F451 devices running firmware 1.0.0.7 and prioritize them for replacement or isolation

Patch Information

No vendor advisory or firmware update is listed in the NVD entry for CVE-2026-6121 at the time of publication. Administrators should monitor the Tenda Official Website for firmware updates addressing the WrlclientSet overflow. Where a fix is not forthcoming, replacing affected end-of-support hardware is the most reliable mitigation.

Workarounds

• Place affected routers behind an upstream firewall that blocks inbound HTTP and HTTPS traffic to the management interface
• Segment the router management VLAN from user and guest networks to reduce authenticated attack surface
• Apply web application firewall or intrusion prevention rules that drop requests to /goform/WrlclientSet containing oversized parameters

# Example iptables rule to restrict access to the Tenda management interface
iptables -A INPUT -p tcp --dport 80 -s 192.168.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.10.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP