CVE-2026-109109: Wavlink WL-WN530BE1-A Buffer Overflow Flaw

CVE-2026-109109 Overview

CVE-2026-109109 is a stack-based buffer overflow affecting the Wavlink WL-WN530BE1-A router running firmware version 251117. The flaw resides in the strcpy call within /cgi-bin/ExportAllSettings.cgi, part of the Settings Export CGI component. Attackers can manipulate the HTTP_COOKIE or X-Cmd argument to overflow a stack buffer. The vulnerability is exploitable remotely without authentication or user interaction. A proof-of-concept exploit is publicly available, and the vendor was notified prior to disclosure.

Critical Impact
Unauthenticated remote attackers can trigger memory corruption on affected Wavlink devices, enabling potential code execution or device compromise over the network.

Affected Products

Wavlink WL-WN530BE1-A router, firmware version 251117
Component: Settings Export CGI (/cgi-bin/ExportAllSettings.cgi)
Vulnerable function: strcpy handling HTTP_COOKIE/X-Cmd input

Discovery Timeline

2026-10-13 - CVE-2026-109109 published to the National Vulnerability Database (NVD)
2026-10-14 - Last updated in NVD database

Technical Details for CVE-2026-109109

Vulnerability Analysis

The vulnerability is a stack-based buffer overflow classified under [CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer]. The flaw exists in the ExportAllSettings.cgi handler on the Wavlink WL-WN530BE1-A device. The CGI binary reads attacker-controlled HTTP headers and passes their contents directly to strcpy without validating length. Because strcpy copies bytes until a null terminator is reached, an oversized header value overwrites adjacent stack memory, including saved return addresses.

Successful exploitation can corrupt control-flow data on the device, enabling remote attackers to crash the service or execute arbitrary code in the context of the CGI process. The CGI typically runs with elevated privileges on embedded router firmware, which expands the blast radius to full device takeover.

Root Cause

The root cause is the use of the unbounded strcpy function to copy untrusted HTTP header data into a fixed-size stack buffer. The handler trusts the length of HTTP_COOKIE and X-Cmd headers supplied by the HTTP client. No length validation, bounds checking, or safer alternatives such as strncpy or strlcpy are used before the copy.

Attack Vector

The attack is network-reachable and requires no authentication or user interaction. An attacker sends a crafted HTTP request to /cgi-bin/ExportAllSettings.cgi on the device's web management interface, embedding an oversized Cookie header or X-Cmd header. When the CGI processes the request, the overflow corrupts the stack and can redirect execution. The exploit is published as a GitHub Gist referenced by VulDB Vulnerability Details and the GitHub Gist PoC.

Detection Methods for CVE-2026-109109

Indicators of Compromise

HTTP requests to /cgi-bin/ExportAllSettings.cgi containing Cookie or X-Cmd header values exceeding a few hundred bytes.
Non-printable or shellcode-like byte sequences within HTTP headers destined for the router's management interface.
Unexpected reboots, crashes, or httpd/CGI process restarts on the Wavlink device following inbound HTTP traffic.

Detection Strategies

Deploy network IDS/IPS signatures that flag abnormally long Cookie and X-Cmd headers directed at Wavlink management endpoints.
Inspect web proxy and firewall logs for requests to ExportAllSettings.cgi sourced from untrusted networks.
Correlate router crash events with preceding inbound HTTP traffic to identify exploitation attempts.

Monitoring Recommendations

Monitor WAN-facing exposure of router administrative interfaces and alert on any unsolicited inbound connections.
Capture full HTTP request headers at the network perimeter to retain forensic evidence of oversized payloads.
Baseline normal management traffic volume and alert on anomalous spikes to /cgi-bin/ endpoints.

How to Mitigate CVE-2026-109109

Immediate Actions Required

Block external access to the router's web management interface and restrict administration to trusted internal networks.
Disable WAN-side HTTP/HTTPS administration on the Wavlink WL-WN530BE1-A if currently enabled.
Monitor the vendor site for updated firmware addressing the ExportAllSettings.cgi buffer overflow.

Patch Information

At the time of publication, no vendor-supplied firmware patch is listed in the referenced advisories. Review the VulDB CVE Summary for updated patch status and consult the Wavlink support channel for firmware releases superseding version 251117.

Workarounds

Place the device behind a network firewall and deny inbound TCP traffic to the management HTTP port from untrusted sources.
Apply ACLs that restrict access to /cgi-bin/ExportAllSettings.cgi to known administrator IP addresses.
Where feasible, replace the affected device with firmware or hardware that is actively maintained by the vendor.

bash

# Example iptables rule restricting router management interface to a trusted subnet
iptables -A INPUT -p tcp --dport 80 -s 192.0.2.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP