CVE-2026-114382: TOTOLINK EX200 Buffer Overflow Vulnerability

CVE-2026-114382 Overview

CVE-2026-114382 is a stack-based buffer overflow in the TOTOLINK EX200 range extender running firmware version 5.2.3c.7200. The flaw resides in the setStaticDhcpConfig function of /cgi-bin/cstecgi.cgi, part of the lan.so component. Attackers manipulate the Comment argument to overflow a fixed-size stack buffer. The vulnerability is exploitable remotely over the network without authentication or user interaction. A public exploit has been released, increasing the likelihood of opportunistic attacks against exposed devices.

Critical Impact
Unauthenticated remote attackers can trigger a stack-based buffer overflow in the TOTOLINK EX200 web management interface, potentially leading to arbitrary code execution on the device.

Affected Products

TOTOLINK EX200 firmware version 5.2.3c.7200
Vulnerable component: lan.so
Vulnerable endpoint: /cgi-bin/cstecgi.cgi (setStaticDhcpConfig function)

Discovery Timeline

2026-10-21 - CVE-2026-114382 published to NVD
2026-10-22 - Last updated in NVD database

Technical Details for CVE-2026-114382

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 is reachable through the CGI handler /cgi-bin/cstecgi.cgi, which dispatches requests to the setStaticDhcpConfig function implemented in lan.so. When a client submits a static DHCP configuration request, the Comment parameter is copied into a fixed-size stack buffer without bounds checking. Supplying a Comment value longer than the destination buffer corrupts adjacent stack memory, including saved return addresses. Because the EX200 web interface accepts the request without authentication, the attack can be launched remotely by any host able to reach the device's management interface.

Root Cause

The root cause is the absence of length validation on attacker-controlled input before it is written to a stack-allocated buffer inside setStaticDhcpConfig. The handler trusts the caller-supplied Comment string and uses an unsafe copy routine, which permits writing beyond the buffer boundary into saved registers and return addresses.

Attack Vector

An attacker sends a crafted HTTP POST request to /cgi-bin/cstecgi.cgi targeting the setStaticDhcpConfig topic, with an oversized Comment field. Successful exploitation corrupts the call stack and can redirect execution flow. Given that the device runs the CGI as a privileged process on the embedded Linux firmware, successful code execution grants attacker control over the router. See the public GitHub report and the VulDB entry for additional technical context.

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

Detection Methods for CVE-2026-114382

Indicators of Compromise

HTTP POST requests to /cgi-bin/cstecgi.cgi referencing the setStaticDhcpConfig action with abnormally long Comment field values.
Unexpected reboots, crashes, or service restarts of the TOTOLINK EX200 web management daemon.
New or unknown static DHCP reservations appearing in the LAN configuration.
Outbound connections from the router to unfamiliar hosts following suspicious management-interface activity.

Detection Strategies

Inspect network traffic for POST bodies to /cgi-bin/cstecgi.cgi whose Comment parameter exceeds a conservative length threshold (for example, more than 64 bytes).
Alert on HTTP requests to the EX200 management interface originating from WAN-facing or untrusted network segments.
Correlate CGI request anomalies with device availability loss or unexpected configuration drift.

Monitoring Recommendations

Enable syslog forwarding from the router (where supported) to a central log collector for continuous review.
Baseline normal administrative traffic to the management interface and alert on deviations.
Review firewall and NAT rules to confirm the EX200 web interface is not exposed to the internet.

How to Mitigate CVE-2026-114382

Immediate Actions Required

Restrict access to the EX200 web management interface to trusted management VLANs or hosts only.
Confirm the device is not reachable from the internet; disable remote management if enabled.
Change the device administrator credentials and audit static DHCP reservations for unauthorized entries.
Monitor the TOTOLINK official site for a firmware update addressing 5.2.3c.7200.

Patch Information

At the time of publication, no vendor-supplied firmware patch is referenced in the NVD entry for CVE-2026-114382. Administrators should track the VulDB advisory and the TOTOLINK support site for a corrective firmware release.

Workarounds

Place the EX200 behind a firewall that blocks inbound connections to TCP ports hosting the web management interface.
Disable the WAN-side HTTP/HTTPS administration service.
Segment the router onto a dedicated management network isolated from untrusted clients and guest Wi-Fi.
If the device is end-of-life or an updated firmware is unavailable, consider replacing it with a supported model.

bash

# Example: block inbound access to the EX200 management interface on an upstream firewall
iptables -A FORWARD -p tcp -d <EX200_IP> --dport 80  -j DROP
iptables -A FORWARD -p tcp -d <EX200_IP> --dport 443 -j DROP