CVE-2026-11522: Tenda W20E Buffer Overflow Vulnerability

CVE-2026-11522 Overview

CVE-2026-11522 is a stack-based buffer overflow in the Tenda W20E router running firmware version 15.11.0.6. The flaw resides in the formSetPortMirror function handler at the /goform/setPortMirror endpoint. Attackers manipulate the portMirrorMirroredPorts parameter to overflow a fixed-size stack buffer. Exploitation occurs over the network and can compromise the confidentiality, integrity, and availability of the affected device. Public exploit details are available, increasing the likelihood of opportunistic abuse against exposed devices. The weakness is classified under [CWE-119] for improper restriction of operations within the bounds of a memory buffer.

Critical Impact

Remote attackers with low-privilege access can corrupt router memory through /goform/setPortMirror, enabling code execution or device crash on Tenda W20E firmware 15.11.0.6.

Affected Products

• Tenda W20E router
• Firmware version 15.11.0.6
• formSetPortMirror handler in /goform/setPortMirror

Discovery Timeline

• 2026-06-08 - CVE-2026-11522 published to the National Vulnerability Database
• 2026-06-09 - Last updated in NVD database

Technical Details for CVE-2026-11522

Vulnerability Analysis

The Tenda W20E web management interface exposes the /goform/setPortMirror endpoint to handle port mirroring configuration. The backend handler formSetPortMirror reads attacker-controlled HTTP parameters and copies them into fixed-size stack buffers without validating length. Submitting an oversized portMirrorMirroredPorts value overwrites adjacent stack memory, including the saved return address. The flaw maps to [CWE-119], improper restriction of operations within the bounds of a memory buffer.

Successful exploitation can hijack control flow on the router's MIPS or ARM SoC, depending on the hardware revision. At minimum, the overflow crashes the httpd process and forces a watchdog reboot, disrupting connectivity for all clients behind the device.

Root Cause

The root cause is the absence of bounds checking on the portMirrorMirroredPorts argument before it is copied into a stack-allocated buffer inside formSetPortMirror. The handler trusts the length of HTTP POST data supplied by the client. No upper bound is enforced on the parameter, and no canary or stack protection mitigates the corruption on the shipping firmware.

Attack Vector

An attacker sends a crafted HTTP POST request to /goform/setPortMirror with an oversized portMirrorMirroredPorts value. The request requires authenticated access to the router management interface, but default or weak credentials are common in this device class. The attack is reachable over LAN by default and over the WAN when remote administration is enabled. Detailed reproduction steps and proof-of-concept payload structures are documented in the public GitHub IoT Vulnerability Report and the VulDB entry for CVE-2026-11522.

Detection Methods for CVE-2026-11522

Indicators of Compromise

• HTTP POST requests to /goform/setPortMirror containing unusually long portMirrorMirroredPorts values exceeding expected port-list lengths.
• Repeated httpd process crashes or watchdog-triggered reboots on Tenda W20E devices.
• Unexpected configuration changes to port mirroring rules following inbound management traffic.

Detection Strategies

• Inspect web server access logs for POST bodies to /goform/setPortMirror that contain non-numeric or oversized data in the portMirrorMirroredPorts field.
• Deploy network IDS signatures that flag HTTP requests to Tenda /goform/ endpoints with payload sizes outside normal parameter bounds.
• Correlate router reboot events with preceding management-plane HTTP traffic to identify exploitation attempts.

Monitoring Recommendations

• Forward router syslog and HTTP access logs to a central SIEM for anomaly analysis.
• Alert on any administrative HTTP requests originating from untrusted network segments or external IP ranges.
• Track firmware versions across the fleet and flag devices still running Tenda W20E 15.11.0.6.

How to Mitigate CVE-2026-11522

Immediate Actions Required

• Disable remote (WAN-side) administration of the Tenda W20E web interface until a vendor patch is verified.
• Restrict LAN-side access to /goform/setPortMirror to a dedicated management VLAN.
• Rotate router administrator credentials and remove any default or shared passwords.
• Monitor the Tenda official website for firmware updates addressing the formSetPortMirror overflow.

Patch Information

At the time of publication, no vendor advisory or fixed firmware version has been linked to CVE-2026-11522 in the NVD record. Administrators should track the VulDB vulnerability page and Tenda's support channels for an updated firmware release that replaces the unsafe copy in formSetPortMirror with a bounded operation.

Workarounds

• Block external access to TCP ports 80 and 443 on the router's WAN interface using upstream firewall rules.
• Place vulnerable devices behind a network segment that enforces authenticated VPN access for management.
• Replace the affected Tenda W20E hardware where management exposure cannot be controlled and a firmware fix is unavailable.

# Configuration example: upstream firewall rule to block WAN management access
iptables -A FORWARD -p tcp -d <router_wan_ip> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <router_wan_ip> --dport 443 -j DROP