CVE-2026-11503: Tenda CX12L Buffer Overflow Vulnerability

CVE-2026-11503 Overview

CVE-2026-11503 is a stack-based buffer overflow vulnerability in the Tenda CX12L router running firmware version 16.03.53.12. The flaw resides in the form_fast_setting_wifi_set function exposed through the /goform/fast_setting_wifi_set endpoint, which handles Wi-Fi configuration requests. Attackers can trigger the overflow by manipulating the ssid parameter sent to the Wi-Fi Configuration Endpoint. The vulnerability is remotely exploitable, and the exploit has been disclosed publicly. The issue maps to [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Critical Impact
Remote attackers with low-privileged access can corrupt stack memory on affected Tenda CX12L routers, enabling potential arbitrary code execution and full device compromise.

Affected Products

Tenda CX12L router
Firmware version 16.03.53.12
Wi-Fi Configuration Endpoint (/goform/fast_setting_wifi_set)

Discovery Timeline

2026-06-08 - CVE-2026-11503 published to NVD
2026-06-08 - Last updated in NVD database

Technical Details for CVE-2026-11503

Vulnerability Analysis

The vulnerability exists in the form_fast_setting_wifi_set function handling requests to /goform/fast_setting_wifi_set. This endpoint processes Wi-Fi quick-setup data submitted by the router's web management interface. The handler copies the user-supplied ssid argument into a fixed-size stack buffer without enforcing proper length validation. Sending an oversized ssid value overruns the buffer and overwrites adjacent stack memory, including saved return addresses. The condition is reachable across the network with low privileges and no user interaction. Successful exploitation can lead to denial of service or arbitrary code execution in the context of the router's web service, which typically runs with elevated privileges on embedded Linux firmware.

Root Cause

The root cause is the absence of bounds checking on the ssid parameter before it is written into a stack-allocated buffer inside form_fast_setting_wifi_set. The function appears to rely on unsafe string-copy operations against attacker-controlled input, a pattern consistent with [CWE-119] memory boundary violations frequently found in Tenda's httpd-based goform handlers.

Attack Vector

An authenticated attacker on the network sends a crafted HTTP POST request to /goform/fast_setting_wifi_set containing an oversized ssid value. The malformed request reaches the vulnerable handler, where the unchecked copy operation overwrites the stack frame. Because the device exposes this endpoint over its LAN-side web interface, and in some deployments over WAN, the attack can be launched remotely without user interaction. A public exploit has been disclosed through the GitHub Issue Tracker and indexed by VulDB.

No verified proof-of-concept code is available for direct reproduction in this article. Refer to the linked VulDB and GitHub references for technical details.

Detection Methods for CVE-2026-11503

Indicators of Compromise

HTTP POST requests to /goform/fast_setting_wifi_set containing abnormally long ssid values exceeding typical SSID length limits (32 bytes).
Unexpected httpd process crashes, restarts, or watchdog-triggered reboots on Tenda CX12L devices.
Outbound connections from the router to unfamiliar hosts following management-plane activity.

Detection Strategies

Inspect web traffic destined for Tenda router management interfaces for malformed parameters in goform endpoints.
Apply intrusion detection signatures matching oversized ssid fields in HTTP request bodies targeting /goform/fast_setting_wifi_set.
Correlate router log anomalies, including service restarts, with management-plane HTTP requests from unexpected sources.

Monitoring Recommendations

Forward router syslog data to a centralized log platform and alert on repeated httpd crashes or unexpected reboots.
Monitor LAN segments for unauthorized HTTP requests targeting /goform/ paths from non-administrator hosts.
Track configuration changes to Wi-Fi SSID, encryption, and password settings outside of approved maintenance windows.

How to Mitigate CVE-2026-11503

Immediate Actions Required

Restrict access to the router's web management interface to trusted administrative hosts only and disable WAN-side remote management.
Change default and weak administrator credentials to reduce risk from low-privilege authenticated attackers.
Segment IoT and consumer-grade networking equipment from sensitive corporate networks.
Monitor the Tenda Official Website for firmware updates addressing this vulnerability.

Patch Information

No vendor patch has been referenced in the published advisory data at the time of writing. Operators of affected Tenda CX12L devices running firmware 16.03.53.12 should monitor VulDB CVE-2026-11503 and Tenda's official support channels for a security firmware update. Until a fix is released, apply network-level compensating controls.

Workarounds

Block external access to TCP ports used by the router's web management service through upstream firewall rules.
Disable Wi-Fi quick-setup functionality through the administrative interface if the feature is not required operationally.
Place vulnerable routers behind a network appliance capable of inspecting and filtering HTTP requests to /goform/fast_setting_wifi_set for oversized parameters.
Replace affected devices with patched hardware or alternative routers where a vendor fix is unlikely to be released promptly.

bash

# Example upstream firewall rule restricting router management access
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -s <admin_workstation_ip> -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -j DROP