CVE-2026-5684: Tenda CX12L Buffer Overflow Vulnerability

CVE-2026-5684 Overview

CVE-2026-5684 is a stack-based buffer overflow vulnerability in the Tenda CX12L router running firmware version 16.03.53.12. The flaw resides in the fromwebExcptypemanFilter function handling requests to /goform/webExcptypemanFilter. An attacker on the adjacent network can manipulate the page argument to overflow a fixed-size stack buffer. Successful exploitation can corrupt control-flow data on the stack, leading to denial of service or arbitrary code execution on the device. The exploit has been publicly disclosed, increasing the likelihood of opportunistic targeting against exposed Tenda CX12L deployments. The weakness is tracked as [CWE-119].

Critical Impact
An authenticated attacker on the local network can corrupt router memory through the page parameter and gain code execution on the affected Tenda CX12L device.

Affected Products

Tenda CX12L firmware version 16.03.53.12
Tenda CX12L hardware device
Endpoint: /goform/webExcptypemanFilter handler fromwebExcptypemanFilter

Discovery Timeline

2026-04-06 - CVE-2026-5684 published to the National Vulnerability Database
2026-04-30 - Last updated in NVD database

Technical Details for CVE-2026-5684

Vulnerability Analysis

The vulnerability exists in the HTTP handler fromwebExcptypemanFilter, which processes requests sent to /goform/webExcptypemanFilter on the router's web management interface. The handler reads the page query parameter and copies its contents into a fixed-size stack buffer without enforcing length validation. Supplying an oversized value for page writes past the buffer boundary and corrupts adjacent stack frame data, including the saved return address. Because the affected binary on embedded MIPS or ARM Tenda firmware typically lacks stack canaries and full Address Space Layout Randomization (ASLR), an attacker can redirect execution to a controlled payload. The flaw requires an attacker who can reach the management interface from the adjacent network and who holds low-privilege credentials. Public disclosure of exploitation details lowers the bar for reuse by opportunistic actors. Full technical context is available in the VulDB Vulnerability #355511 record and the GitHub Issue Discussion.

Root Cause

The root cause is missing bounds checking on user-supplied input during string copy operations inside fromwebExcptypemanFilter. The function trusts the length of the page argument and writes it into a stack-allocated buffer of insufficient size. This is a classic [CWE-119] improper restriction of operations within the bounds of a memory buffer.

Attack Vector

Exploitation requires network adjacency, meaning the attacker must reside on the same LAN or wireless segment as the device, plus low-level authenticated access to the web interface. The attacker issues a crafted HTTP request to /goform/webExcptypemanFilter with an oversized page parameter. No user interaction is required on the victim side. Successful exploitation impacts confidentiality, integrity, and availability of the router. The vulnerability mechanism is documented in the VulDB CTI for #355511 feed; no verified proof-of-concept code is reproduced here.

Detection Methods for CVE-2026-5684

Indicators of Compromise

HTTP requests to /goform/webExcptypemanFilter containing unusually long page parameter values, typically exceeding several hundred bytes.
Router reboots, web administration crashes, or httpd process restarts following inbound LAN HTTP traffic.
Outbound connections from the router to unexpected hosts after web interface access, suggesting post-exploitation command-and-control activity.

Detection Strategies

Inspect LAN traffic for HTTP requests targeting /goform/webExcptypemanFilter and flag requests where the page argument exceeds a reasonable length threshold.
Correlate router syslog events for httpd segmentation faults or watchdog-triggered reboots with prior management-plane HTTP requests.
Apply network intrusion detection signatures matching oversized parameter patterns against Tenda /goform/ endpoints.

Monitoring Recommendations

Forward router logs to a central log platform and alert on repeated authentication followed by malformed /goform/ requests.
Monitor administrative interface access from non-administrator hosts on the LAN and from guest wireless segments.
Track firmware versions across deployed Tenda CX12L devices and flag any unit running 16.03.53.12 until patched.

How to Mitigate CVE-2026-5684

Immediate Actions Required

Restrict access to the router web administration interface to a dedicated management VLAN or trusted host list.
Disable remote management and verify that the web interface is not reachable from the WAN side.
Rotate administrator credentials on all Tenda CX12L devices to invalidate any previously captured low-privilege accounts.
Isolate guest wireless networks from the management subnet to remove adjacent-network reachability.

Patch Information

At the time of publication, no vendor patch has been confirmed for Tenda CX12L firmware 16.03.53.12. Monitor the Tenda Official Website for firmware updates addressing fromwebExcptypemanFilter. Track status through the GitHub Issue Discussion and the VulDB Submission #792781 entry.

Workarounds

Place the router management interface behind an access control list permitting only specific administrator IP addresses.
Segment the network so that untrusted clients, IoT devices, and guests cannot reach the router's web service on TCP/80 or TCP/443.
Replace affected Tenda CX12L units with patched hardware where feasible until a fixed firmware release is available.

bash

# Example: restrict router admin interface to a single management host using iptables
# Run on an upstream firewall, not on the vulnerable device
iptables -A FORWARD -p tcp -d 192.0.2.1 --dport 80 -s 192.0.2.50 -j ACCEPT
iptables -A FORWARD -p tcp -d 192.0.2.1 --dport 80 -j DROP