CVE-2026-4180: D-Link DIR-816 Auth Bypass Vulnerability

CVE-2026-4180 Overview

A vulnerability was identified in D-Link DIR-816 firmware version 1.10CNB05. The impacted element is an unknown function of the file redirect.asp within the goahead web server component. The manipulation of the argument token_id leads to improper access controls (CWE-266). The attack may be initiated remotely without authentication. The exploit is publicly available and might be used. This vulnerability only affects products that are no longer supported by the maintainer.

Critical Impact

Remote attackers can exploit improper access controls in the D-Link DIR-816 router's web interface to bypass authentication mechanisms and potentially gain unauthorized access to device configuration. As this product has reached end-of-life, no official patch will be released.

Affected Products

• D-Link DIR-816 Hardware
• D-Link DIR-816 Firmware version 1.10CNB05
• Goahead web server component within DIR-816 firmware

Discovery Timeline

• 2026-03-16 - CVE-2026-4180 published to NVD
• 2026-03-19 - Last updated in NVD database

Technical Details for CVE-2026-4180

Vulnerability Analysis

This vulnerability stems from improper access control implementation in the D-Link DIR-816 router's web management interface. The flaw exists within the redirect.asp file, which is part of the goahead embedded web server commonly used in IoT devices.

The vulnerability is remotely exploitable over the network without requiring any user interaction or prior authentication. An attacker can manipulate the token_id parameter to bypass intended access restrictions. This type of access control weakness allows unauthorized users to perform actions that should be restricted to authenticated administrators.

The goahead web server component processes HTTP requests and relies on token-based session validation. The improper validation of the token_id parameter creates an opportunity for attackers to forge or manipulate authentication tokens, effectively bypassing the router's security mechanisms.

Root Cause

The root cause is classified as CWE-266 (Incorrect Privilege Assignment). The redirect.asp component fails to properly validate the token_id parameter before processing requests. This improper access control allows attackers to bypass authentication checks that would normally restrict access to privileged functionality. The goahead web server does not adequately verify that the provided token corresponds to a valid authenticated session.

Attack Vector

The attack can be initiated remotely over the network. An attacker with network access to the router's web management interface can send crafted HTTP requests to the redirect.asp endpoint with manipulated token_id values. The attack requires no authentication and no user interaction, making it particularly dangerous for exposed devices.

The vulnerability affects the web interface typically accessible on ports 80 or 443. Attackers on the local network, or those who can reach internet-exposed management interfaces, can exploit this flaw to gain unauthorized access to router configuration and potentially compromise network security.

Technical details and proof-of-concept information are available at the GitHub PoC Repository.

Detection Methods for CVE-2026-4180

Indicators of Compromise

• Unusual HTTP requests targeting /redirect.asp with abnormal or malformed token_id parameter values
• Unauthorized configuration changes on D-Link DIR-816 routers without corresponding administrator login events
• Unexpected traffic patterns to the router's web management interface from external IP addresses
• Log entries showing access to administrative functions without proper authentication sequences

Detection Strategies

• Monitor web server logs for repeated requests to redirect.asp with varying token_id parameter values, which may indicate exploitation attempts
• Implement network intrusion detection rules to alert on suspicious HTTP traffic targeting D-Link router management interfaces
• Deploy honeypot routers running vulnerable firmware versions to detect active scanning and exploitation campaigns
• Review router access logs for administrative actions that lack corresponding authentication events

Monitoring Recommendations

• Enable logging on network firewalls to capture all traffic destined for router management interfaces
• Implement SIEM rules to correlate authentication bypass indicators across multiple network devices
• Regularly audit router configurations for unauthorized changes that may indicate successful exploitation
• Monitor threat intelligence feeds for campaigns targeting D-Link DIR-816 devices, referencing VulDB CTI ID #351084

How to Mitigate CVE-2026-4180

Immediate Actions Required

• Disable remote web management access on affected D-Link DIR-816 routers immediately
• Restrict access to the router's management interface to trusted IP addresses only using firewall rules
• Consider replacing end-of-life DIR-816 devices with currently supported router models
• Isolate affected devices on a separate network segment if replacement is not immediately possible

Patch Information

No official patch is available for this vulnerability. D-Link has confirmed that the DIR-816 version 1.10CNB05 is no longer supported and has reached end-of-life status. Users should consider the following options:

1. Device Replacement: Replace the D-Link DIR-816 with a currently supported router model that receives security updates
2. Third-party Firmware: Investigate whether alternative open-source firmware (such as OpenWrt or DD-WRT) supports your hardware model and provides better security
3. Network Isolation: If replacement is not feasible, implement strict network segmentation to limit exposure

For more information, visit the D-Link Official Website.

Workarounds

• Disable the web management interface entirely if device configuration changes are not frequently required
• Configure firewall rules to block all external access to the router's management ports (typically TCP 80 and 443)
• Enable MAC address filtering on the management interface to restrict access to known administrator devices
• Deploy a separate firewall or access control device in front of the vulnerable router to filter malicious requests

# Example firewall rules to restrict management interface access
# Block external access to router management on WAN interface
iptables -A INPUT -i eth0 -p tcp --dport 80 -j DROP
iptables -A INPUT -i eth0 -p tcp --dport 443 -j DROP

# Allow management access only from specific trusted IP
iptables -A INPUT -i br0 -s 192.168.1.100 -p tcp --dport 80 -j ACCEPT
iptables -A INPUT -i br0 -p tcp --dport 80 -j DROP