CVE-2026-4183: D-Link DIR-816 Buffer Overflow Vulnerability

CVE-2026-4183 Overview

A stack-based buffer overflow vulnerability has been identified in the D-Link DIR-816 router firmware version 1.10CNB05. The vulnerability exists in an unspecified function within the /goform/form2WlanBasicSetup.cgi file of the goahead web server component. Remote attackers can exploit this vulnerability by manipulating the pskValue argument, potentially leading to arbitrary code execution or denial of service conditions. This vulnerability affects a product that is no longer supported by the maintainer, leaving no official patches available.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to potentially execute arbitrary code or cause system crashes on affected D-Link DIR-816 routers running firmware version 1.10CNB05. The exploit has been publicly disclosed, increasing the risk of active exploitation.

Affected Products

• D-Link DIR-816 Firmware version 1.10CNB05
• D-Link DIR-816 Hardware

Discovery Timeline

• 2026-03-16 - CVE-2026-4183 published to NVD
• 2026-03-19 - Last updated in NVD database

Technical Details for CVE-2026-4183

Vulnerability Analysis

This vulnerability is a classic stack-based buffer overflow (CWE-787: Out-of-bounds Write, CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer) affecting the embedded web server on D-Link DIR-816 routers. The vulnerability resides in the handling of the pskValue parameter within the wireless configuration CGI endpoint. When processing user-supplied input for the wireless pre-shared key value, the affected function fails to properly validate the length of input data before copying it to a fixed-size stack buffer.

The goahead web server component processes HTTP requests to /goform/form2WlanBasicSetup.cgi, which handles wireless network basic setup operations. An attacker can craft a malicious request containing an oversized pskValue parameter that exceeds the allocated buffer size, causing stack memory corruption.

Root Cause

The root cause of this vulnerability is improper input validation in the wireless setup CGI handler. The application does not adequately check the length of the pskValue parameter before copying it into a stack-allocated buffer. This allows attackers to supply a value larger than the expected buffer size, overwriting adjacent memory on the stack including potentially the return address.

The lack of boundary checking on user-controlled input, combined with the absence of modern exploit mitigations commonly missing in embedded devices (such as stack canaries or ASLR), makes this vulnerability particularly dangerous.

Attack Vector

The attack can be executed remotely over the network without requiring authentication. An attacker with network access to the router's web management interface can submit a crafted HTTP POST request to the vulnerable CGI endpoint. The attack involves the following methodology:

1. The attacker identifies a D-Link DIR-816 router running vulnerable firmware 1.10CNB05
2. A specially crafted HTTP request is sent to /goform/form2WlanBasicSetup.cgi
3. The pskValue parameter is populated with malicious data exceeding the expected buffer size
4. The overflow corrupts stack memory, potentially allowing control flow hijacking
5. Depending on exploitation sophistication, this could lead to arbitrary code execution with router privileges

The vulnerability is exploitable remotely via network access, requires no privileges or user interaction, and can result in complete compromise of the router's confidentiality, integrity, and availability. Technical documentation of this vulnerability is available in the GitHub Vulnerability Documentation.

Detection Methods for CVE-2026-4183

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/form2WlanBasicSetup.cgi with abnormally large pskValue parameters
• Router crashes, reboots, or unresponsive behavior following web interface access attempts
• Unusual network traffic patterns originating from the router's management interface
• Modified router configuration or unexpected administrative changes

Detection Strategies

• Monitor network traffic for HTTP requests to /goform/form2WlanBasicSetup.cgi containing oversized parameter values
• Implement IDS/IPS rules to detect buffer overflow attack patterns targeting D-Link router CGI endpoints
• Deploy network segmentation to isolate vulnerable router management interfaces from untrusted networks
• Use web application firewalls to filter malicious requests with abnormal parameter lengths

Monitoring Recommendations

• Enable logging on network perimeter devices to capture traffic destined for router management interfaces
• Implement alerts for unusual HTTP request patterns targeting embedded device web servers
• Regularly audit network for D-Link DIR-816 devices running firmware version 1.10CNB05
• Monitor for indicators of router compromise such as DNS hijacking or traffic redirection

How to Mitigate CVE-2026-4183

Immediate Actions Required

• Isolate affected D-Link DIR-816 routers from external network access immediately
• Disable remote web management access to the router's administrative interface
• Implement network-level access controls to restrict management interface access to trusted IPs only
• Consider replacing end-of-life hardware with currently supported networking equipment

Patch Information

D-Link has classified the DIR-816 as an end-of-life product that is no longer supported. As such, no official security patches are available or expected for this vulnerability. Organizations using affected devices should prioritize hardware replacement with actively supported alternatives.

For additional vulnerability details, refer to VulDB #351087 or visit the D-Link Official Website for information on supported products.

Workarounds

• Disable WAN-side access to the router's web management interface entirely
• Implement strict firewall rules blocking external access to the router's HTTP/HTTPS ports
• Use a separate, supported firewall device in front of the vulnerable router
• Replace the DIR-816 with a currently supported D-Link model or alternative vendor hardware

# Configuration example - Network-level mitigation using iptables on upstream device
# Block external access to router management interface
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 443 -j DROP

# Allow management access only from trusted admin workstation
iptables -I FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT