CVE-2026-4182: D-Link DIR-816 Buffer Overflow Vulnerability

CVE-2026-4182 Overview

A stack-based buffer overflow vulnerability has been identified in D-Link DIR-816 wireless routers running firmware version 1.10CNB05. The vulnerability exists in the goahead web server component, specifically within the /goform/form2Wl5RepeaterStep2.cgi handler. Attackers can exploit this flaw by manipulating the key1, key2, key3, key4, or pskValue arguments to trigger a buffer overflow condition, potentially leading to remote code execution on the affected device.

Critical Impact

This vulnerability allows unauthenticated remote attackers to execute arbitrary code on vulnerable D-Link DIR-816 routers. The exploit has been publicly disclosed, and D-Link has confirmed this product is end-of-life with no planned security patches.

Affected Products

• D-Link DIR-816 Firmware version 1.10CNB05
• D-Link DIR-816 Hardware (all revisions running affected firmware)

Discovery Timeline

• 2026-03-16 - CVE-2026-4182 published to NVD
• 2026-03-19 - Last updated in NVD database

Technical Details for CVE-2026-4182

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-787: Out-of-bounds Write, CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the goahead embedded web server that handles administrative functions on the DIR-816 router.

The affected CGI handler /goform/form2Wl5RepeaterStep2.cgi processes wireless repeater configuration requests but fails to properly validate the length of user-supplied input for the key1, key2, key3, key4, and pskValue parameters. When an attacker supplies oversized values for these parameters, the data overflows the allocated stack buffer, corrupting adjacent memory regions including saved return addresses and other critical stack data.

This memory corruption can be leveraged by sophisticated attackers to gain control of program execution flow, potentially achieving arbitrary code execution with the privileges of the web server process (typically root on embedded devices).

Root Cause

The root cause of this vulnerability is improper input validation and the use of unsafe memory copy operations when handling user-supplied wireless key parameters. The CGI handler allocates a fixed-size buffer on the stack to store the key values but does not verify that the input data fits within the allocated space before copying it.

This type of vulnerability is common in embedded systems and IoT devices where memory constraints lead developers to use fixed-size buffers, and security practices may be sacrificed for performance or simplicity.

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 send a specially crafted HTTP POST request to the vulnerable CGI endpoint. The malicious request would contain oversized values for the wireless key parameters, designed to overflow the stack buffer and overwrite the return address with an attacker-controlled value.

On successful exploitation, the attacker could:

• Execute arbitrary code on the router with root privileges
• Install persistent backdoors or malware
• Intercept or modify network traffic
• Pivot to attack other devices on the network
• Disable security features or brick the device

The exploit has been made publicly available, increasing the risk of widespread attacks against vulnerable devices. Technical details and proof-of-concept information can be found in the GitHub Vulnerability Documentation.

Detection Methods for CVE-2026-4182

Indicators of Compromise

• Unusual HTTP POST requests to /goform/form2Wl5RepeaterStep2.cgi containing abnormally long parameter values
• Unexpected router reboots or crashes following web interface access
• Unauthorized changes to wireless configuration settings
• Unusual outbound network connections originating from the router
• Presence of unknown processes or modified firmware files on the device

Detection Strategies

• Monitor web server logs for requests to /goform/form2Wl5RepeaterStep2.cgi with oversized key1, key2, key3, key4, or pskValue parameters
• Implement network intrusion detection rules to flag HTTP requests with excessively long wireless key values targeting D-Link routers
• Use firmware integrity checking tools to detect unauthorized modifications to router software
• Deploy network traffic analysis to identify anomalous behavior patterns from IoT devices

Monitoring Recommendations

• Enable logging on router management interfaces and forward logs to a centralized SIEM solution
• Implement network segmentation to isolate IoT devices from critical infrastructure
• Configure alerts for any administrative access attempts to end-of-life network equipment
• Regularly scan network for devices running vulnerable D-Link firmware versions

How to Mitigate CVE-2026-4182

Immediate Actions Required

• Immediately isolate affected D-Link DIR-816 devices from untrusted networks
• Disable remote management interfaces if possible, limiting access to local network only
• Consider replacing end-of-life DIR-816 routers with currently supported alternatives
• Implement network access controls to restrict who can reach the router's management interface

Patch Information

D-Link has confirmed that the DIR-816 router is an end-of-life product and will not receive security patches for this vulnerability. D-Link recommends replacing affected devices with current, supported router models. For more information, visit the D-Link Official Website.

Additional vulnerability tracking information is available at VulDB #351086.

Workarounds

• Restrict access to the router's web management interface using firewall rules or ACLs to allow only trusted IP addresses
• Disable the web management interface entirely if not required for ongoing administration
• Place the router behind a firewall that can filter and inspect HTTP traffic to the device
• Consider using third-party firmware alternatives (such as OpenWrt or DD-WRT) if compatible with your hardware revision

# Example iptables rules to restrict management access (on upstream firewall)
# Allow management access only from trusted admin workstation
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
# Replace 192.168.1.1 with router IP and 192.168.1.100 with trusted admin IP