CVE-2026-11524: Tenda W20E Buffer Overflow Vulnerability

CVE-2026-11524 Overview

CVE-2026-11524 is a stack-based buffer overflow vulnerability in the Tenda W20E router running firmware version 15.11.0.6. The flaw exists in the modifyWifiFilterRules function handling requests to /goform/modifyWifiFilterRules within the Web Management Interface. Attackers can trigger the overflow by manipulating the wifiFilterListRemark argument. The vulnerability is remotely exploitable and has been publicly disclosed, increasing the risk of weaponization against exposed devices. The weakness is classified under CWE-119 covering improper restriction of operations within the bounds of a memory buffer.

Critical Impact

Remote authenticated attackers can corrupt the stack of Tenda W20E routers via the wifiFilterListRemark parameter, enabling potential arbitrary code execution and full device compromise.

Affected Products

• Tenda W20E router
• Firmware version 15.11.0.6
• Web Management Interface component (/goform/modifyWifiFilterRules endpoint)

Discovery Timeline

• 2026-06-08 - CVE-2026-11524 published to NVD
• 2026-06-09 - Last updated in NVD database

Technical Details for CVE-2026-11524

Vulnerability Analysis

The vulnerability resides in the modifyWifiFilterRules function exposed by the Tenda W20E Web Management Interface. When a request reaches /goform/modifyWifiFilterRules, the handler reads the wifiFilterListRemark parameter from the HTTP body and copies it into a fixed-size stack buffer without enforcing length validation. Supplying an oversized value overruns the buffer and corrupts adjacent stack memory, including saved return addresses. Successful exploitation can hijack control flow and achieve arbitrary code execution on the embedded device. The attack requires network reachability to the management interface and low-privileged authentication.

Root Cause

The root cause is missing bounds checking on user-controlled input copied into a stack-allocated buffer. The modifyWifiFilterRules handler trusts the length of the wifiFilterListRemark field and performs an unbounded copy operation, matching the pattern described by CWE-119. Embedded MIPS-based Tenda firmware historically lacks modern stack protection mitigations, which amplifies the impact of this class of flaw.

Attack Vector

An attacker with network access to the router's management interface sends a crafted POST request to /goform/modifyWifiFilterRules containing an oversized wifiFilterListRemark value. If the management interface is exposed to untrusted networks or the WAN, the attack surface extends beyond the local LAN. Technical details and proof-of-concept information have been published. See the GitHub IoT Vulnerability Report and VulDB CVE-2026-11524 entry for additional context.

No verified exploit code is reproduced here. Refer to the linked advisory for proof-of-concept details.

Detection Methods for CVE-2026-11524

Indicators of Compromise

• HTTP POST requests to /goform/modifyWifiFilterRules containing unusually long wifiFilterListRemark parameter values.
• Unexpected reboots, crashes, or watchdog resets of Tenda W20E devices following web interface activity.
• Outbound connections from the router to unknown hosts following management interface access.
• New or modified firewall and filter rules that were not initiated by an administrator.

Detection Strategies

• Deploy network IDS signatures that flag POST requests to /goform/modifyWifiFilterRules exceeding a defined size threshold for the wifiFilterListRemark field.
• Monitor management interface authentication logs for low-privileged accounts issuing configuration changes outside normal patterns.
• Inspect router syslog output for segmentation faults or process restarts originating from the httpd service.

Monitoring Recommendations

• Forward router syslog data to a centralized SIEM and alert on repeated crashes of the web management daemon.
• Track all administrative sessions targeting the W20E management interface, especially from unexpected source IP ranges.
• Audit exposure of router management interfaces to the internet using external attack surface scans.

How to Mitigate CVE-2026-11524

Immediate Actions Required

• Restrict access to the Tenda W20E web management interface to trusted management VLANs only and disable WAN-side administration.
• Rotate all administrative credentials on affected devices and enforce strong, unique passwords.
• Place vulnerable routers behind a network segmentation boundary until a vendor patch is available.
• Audit existing Wi-Fi filter rules and device configuration for unauthorized modifications.

Patch Information

At the time of publication, no vendor patch has been referenced in the NVD entry for CVE-2026-11524. Monitor the Tenda official website for firmware updates addressing the modifyWifiFilterRules function. Apply patches immediately once released and verify firmware integrity after the update.

Workarounds

• Disable remote management on the WAN interface and restrict LAN access to the web UI using ACLs.
• Block external access to /goform/modifyWifiFilterRules via an upstream firewall or reverse proxy where feasible.
• Replace end-of-life or unpatched Tenda W20E devices with currently supported hardware if no firmware fix is released.
• Disable any unused administrative accounts to reduce the low-privilege attack surface required by this vulnerability.

# Configuration example: restrict router management interface to a trusted subnet
# (Apply on an upstream firewall in front of the Tenda W20E)
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -s 10.10.0.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 80 -j DROP
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -s 10.10.0.0/24 -j ACCEPT
iptables -A FORWARD -p tcp -d <router_ip> --dport 443 -j DROP