CVE-2026-11504: Tenda CX12L Buffer Overflow Vulnerability

CVE-2026-11504 Overview

CVE-2026-11504 is a stack-based buffer overflow vulnerability in the Tenda CX12L router running firmware version 16.03.53.12. The flaw exists in the setSchedWifi function within the /goform/openSchedWifi endpoint, which handles Wi-Fi schedule configuration. Attackers can trigger the overflow remotely by manipulating the schedStartTime or schedEndTime arguments. Public exploit details are available, increasing the risk of opportunistic abuse against exposed devices. The vulnerability is tracked under [CWE-119] (Improper Restriction of Operations within the Bounds of a Memory Buffer).

Critical Impact
Remote attackers with low privileges can corrupt stack memory on Tenda CX12L routers, potentially achieving arbitrary code execution and full device compromise.

Affected Products

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

Discovery Timeline

2026-06-08 - CVE-2026-11504 published to the National Vulnerability Database (NVD)
2026-06-08 - Last updated in NVD database

Technical Details for CVE-2026-11504

Vulnerability Analysis

The vulnerability resides in the setSchedWifi function exposed through the /goform/openSchedWifi web interface endpoint. This endpoint accepts user-controlled parameters that configure scheduled Wi-Fi activation windows on the router. The function copies the schedStartTime and schedEndTime parameter values into fixed-size stack buffers without enforcing length validation.

When an attacker submits oversized values for either parameter, the copy operation writes past the buffer boundary and overwrites adjacent stack memory. This includes saved return addresses and stack frame metadata. Successful exploitation can redirect control flow, leading to remote code execution under the privileges of the router web service, typically running as root on embedded Linux firmware.

The exploit has been disclosed publicly, which lowers the barrier for adversaries scanning for vulnerable Tenda devices on the internet.

Root Cause

The root cause is the absence of bounds checking on attacker-controlled string inputs before they are copied into stack-allocated buffers. The setSchedWifi handler uses unsafe string operations on the schedStartTime and schedEndTime request parameters. This matches the [CWE-119] classification for improper memory buffer restrictions.

Attack Vector

The attack vector is network-based against the router's HTTP management interface. An authenticated attacker with low-level privileges sends a crafted POST request to /goform/openSchedWifi containing oversized schedStartTime or schedEndTime values. No user interaction is required to trigger the overflow. The vulnerability manifests during request parsing in the embedded web server. For technical details on the exploitation primitive, refer to the GitHub Issue Discussion and the VulDB CVE-2026-11504 entry.

Detection Methods for CVE-2026-11504

Indicators of Compromise

HTTP POST requests to /goform/openSchedWifi containing unusually long schedStartTime or schedEndTime parameter values
Router crashes, reboots, or web management interface unresponsiveness following requests to the Wi-Fi schedule endpoint
Unexpected outbound connections from the router to attacker-controlled infrastructure after exploitation
Modified router configuration or new administrative sessions originating from untrusted IP addresses

Detection Strategies

Inspect HTTP request payloads to /goform/ endpoints and alert on parameter values exceeding expected length thresholds
Deploy network intrusion detection signatures targeting overlong schedStartTime and schedEndTime fields in requests to Tenda devices
Correlate router availability monitoring with web management traffic to identify exploitation attempts that cause service crashes

Monitoring Recommendations

Enable verbose logging on perimeter firewalls for all inbound traffic reaching router management interfaces
Monitor SOHO and branch-office routers for unscheduled reboots that may indicate exploitation attempts
Track DNS queries and outbound connections originating from router IP addresses for signs of post-exploitation command-and-control activity

How to Mitigate CVE-2026-11504

Immediate Actions Required

Restrict access to the Tenda CX12L web management interface to trusted internal networks only and block external WAN-side administration
Disable the Wi-Fi schedule feature if it is not actively required in your environment
Rotate router administrator credentials and disable default or weak accounts that could supply the low privileges required for exploitation
Inventory all Tenda CX12L devices running firmware 16.03.53.12 and prioritize remediation for internet-exposed units

Patch Information

At the time of publication, no vendor-supplied patch has been referenced in the available advisories. Monitor the Tenda Website for firmware updates addressing CVE-2026-11504. Refer to the VulDB Vulnerability #369124 entry for tracking updates to remediation guidance.

Workarounds

Place affected routers behind a network segment that blocks untrusted access to TCP ports hosting the HTTP management interface
Use access control lists to permit management connections only from designated administrator workstations
Replace end-of-life or unpatched Tenda CX12L devices with hardware that receives active security maintenance if no fix becomes available

bash

# Example iptables rule to restrict router management access to a trusted subnet
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