CVE-2026-75784: TRENDnet TEW-WLC100 Buffer Overflow Flaw

CVE-2026-75784 Overview

CVE-2026-75784 is a stack-based buffer overflow [CWE-119] in the TRENDnet TEW-WLC100 wireless LAN controller running firmware version 1v2.07b01. The flaw resides in function FUN_0040da4c within the embedded nginx binary located at /usr/nginx/sbin/nginx. The HTTP Header Handler improperly processes the Server header, allowing an unauthenticated attacker to trigger memory corruption remotely. A public proof-of-concept exploit is available in a GitHub PoC repository, increasing the likelihood of opportunistic exploitation against exposed devices.

Critical Impact
Remote, unauthenticated attackers can corrupt stack memory in the device's web service, enabling denial of service and potential arbitrary code execution on the controller.

Affected Products

TRENDnet TEW-WLC100 Wireless LAN Controller
Firmware version 1v2.07b01
Embedded nginx HTTP service at /usr/nginx/sbin/nginx

Discovery Timeline

2026-08-18 - CVE-2026-75784 published to NVD
2026-08-20 - Last updated in NVD database

Technical Details for CVE-2026-75784

Vulnerability Analysis

The vulnerability exists inside FUN_0040da4c, a function in the TRENDnet-shipped nginx binary that parses inbound HTTP header fields. When the handler processes the Server header, it copies attacker-controlled data into a fixed-size stack buffer without validating the input length. Oversized input overwrites adjacent stack memory, including saved return addresses and function pointers.

Because the affected service is exposed over the network and requires no authentication, an attacker can trigger the overflow with a single crafted HTTP request. On embedded MIPS or ARM targets like the TEW-WLC100, successful exploitation may bypass weak or absent mitigations such as stack canaries, ASLR, and non-executable memory, escalating from a crash to code execution.

Root Cause

The root cause is missing bounds checking during the copy of the Server HTTP header into a stack-allocated buffer inside FUN_0040da4c. The function trusts the length of client-supplied header data, a classic pattern captured by [CWE-119]: Improper Restriction of Operations within the Bounds of a Memory Buffer.

Attack Vector

Exploitation requires network access to the controller's HTTP management interface. An attacker sends an HTTP request containing an oversized or specially crafted Server header. The vulnerable function copies the payload onto the stack, corrupting control-flow data. The public proof of concept demonstrates the overflow condition; see the GitHub PoC repository and the GitHub CVE code repository for reference. Additional context is available in the VulDB vulnerability details.

Detection Methods for CVE-2026-75784

Indicators of Compromise

HTTP requests to the TEW-WLC100 management interface containing abnormally long Server headers
Repeated crashes or restarts of the nginx process on /usr/nginx/sbin/nginx
Source IPs matching public PoC user-agents or issuing malformed HTTP requests to the controller
Unexpected outbound connections initiated by the controller following inbound HTTP traffic

Detection Strategies

Deploy network IDS/IPS signatures that flag HTTP requests with Server header lengths exceeding standard values (typically over 256 bytes)
Correlate web-server crash events on the controller with inbound HTTP traffic in the same time window
Baseline normal HTTP header sizes to the management interface and alert on statistical outliers
Restrict and monitor administrative access paths to network infrastructure devices

Monitoring Recommendations

Capture full HTTP request headers at the perimeter for any management interface exposed on the network
Log and forward device syslog to a central platform to detect service restarts and segmentation faults
Alert on any external source attempting to reach the TEW-WLC100 web UI
Track known PoC-related URIs and payload patterns published in the referenced repositories

How to Mitigate CVE-2026-75784

Immediate Actions Required

Remove the TEW-WLC100 management interface from any untrusted or internet-facing network segment
Restrict HTTP/HTTPS access to the controller to a dedicated management VLAN and known administrative hosts
Inspect logs for signs of exploitation attempts referencing oversized Server headers
Track vendor communications from TRENDnet for firmware updates addressing CVE-2026-75784

Patch Information

At the time of publication, no vendor patch is listed in the NVD entry or referenced advisories for CVE-2026-75784. Monitor TRENDnet support channels and the VulDB CVE reference for firmware updates covering the TEW-WLC100 running 1v2.07b01.

Workarounds

Place the controller behind a reverse proxy or WAF that enforces strict HTTP header length limits
Block inbound requests containing Server headers greater than the maximum expected size at network boundary devices
Disable remote management on the device where operationally feasible and administer locally
Segment the wireless management plane from user and guest networks to limit lateral exposure

bash

# Example: drop oversized Server headers at an upstream nginx reverse proxy
http {
    map $http_server $blocked_server_header {
        default 0;
        "~^.{256,}$" 1;
    }

    server {
        listen 443 ssl;
        server_name wlc-mgmt.example.local;

        if ($blocked_server_header) {
            return 400;
        }

        location / {
            proxy_pass https://10.10.10.5;
        }
    }
}