CVE-2025-5620: D-Link DIR-816 Firmware RCE Vulnerability

CVE-2025-5620 Overview

A critical OS command injection vulnerability has been discovered in the D-Link DIR-816 wireless router firmware version 1.10CNB05. The vulnerability exists in the setipsec_config function within the /goform/setipsec_config endpoint, where improper handling of the localIP and remoteIP parameters allows attackers to inject and execute arbitrary operating system commands remotely. This vulnerability affects an end-of-life product that is no longer supported by D-Link.

Critical Impact

Unauthenticated remote attackers can execute arbitrary system commands on vulnerable D-Link DIR-816 routers, potentially leading to complete device compromise, network intrusion, and persistent unauthorized access.

Affected Products

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

Discovery Timeline

• June 5, 2025 - CVE-2025-5620 published to NVD
• June 6, 2025 - Last updated in NVD database

Technical Details for CVE-2025-5620

Vulnerability Analysis

This OS command injection vulnerability (CWE-77, CWE-78) stems from insufficient input validation in the IPSec configuration functionality of the D-Link DIR-816 router. The setipsec_config function fails to properly sanitize user-supplied input in the localIP and remoteIP parameters before passing them to system-level command execution functions. An attacker can craft malicious input containing shell metacharacters or command separators to break out of the intended command context and execute arbitrary commands with the privileges of the web server process, typically running as root on embedded devices.

The vulnerability is particularly concerning because the exploit has been publicly disclosed, and the affected product has reached end-of-life status, meaning D-Link will not provide security patches. Devices exposed to the internet are at immediate risk of compromise.

Root Cause

The root cause of CVE-2025-5620 is improper input validation and sanitization in the setipsec_config function. When processing IPSec configuration requests through the /goform/setipsec_config endpoint, the application directly incorporates user-supplied values for localIP and remoteIP parameters into system commands without adequate filtering of shell metacharacters. This allows command injection payloads to be executed in the context of the underlying operating system.

Attack Vector

The attack can be launched remotely over the network without requiring authentication. An attacker can send a specially crafted HTTP request to the /goform/setipsec_config endpoint with malicious payloads embedded in the localIP or remoteIP parameters. By including shell command separators (such as semicolons, pipes, or backticks) followed by arbitrary commands, the attacker can achieve remote code execution on the vulnerable router.

The exploitation mechanism involves:

1. Sending a crafted HTTP POST request to /goform/setipsec_config
2. Including command injection payloads in the localIP or remoteIP parameters
3. The vulnerable function executes the injected commands with system privileges
4. Attacker gains command execution capability on the router

For detailed technical analysis of this vulnerability, refer to the GitHub Vulnerability Documentation.

Detection Methods for CVE-2025-5620

Indicators of Compromise

• Unusual HTTP POST requests to /goform/setipsec_config containing shell metacharacters (;, |, $(), backticks) in the localIP or remoteIP parameters
• Unexpected outbound network connections from router devices to external IP addresses
• Presence of unauthorized user accounts, SSH keys, or modified configuration files on the router
• Suspicious processes spawning from the web server process on the router

Detection Strategies

• Implement network-based intrusion detection rules to identify HTTP requests targeting /goform/setipsec_config with command injection patterns
• Monitor router logs for unusual configuration change attempts or failed authentication attempts
• Deploy honeypot routers to capture exploitation attempts targeting D-Link devices
• Use vulnerability scanning tools to identify exposed DIR-816 devices in your network

Monitoring Recommendations

• Enable logging on all network perimeter devices to capture traffic to and from D-Link routers
• Implement DNS monitoring to detect suspicious domain resolutions from router IP addresses
• Monitor for unusual firmware modifications or configuration changes on affected devices
• Set up alerts for any traffic anomalies originating from router management interfaces

How to Mitigate CVE-2025-5620

Immediate Actions Required

• Immediately remove D-Link DIR-816 devices from production networks as they are end-of-life and will not receive security updates
• If immediate replacement is not possible, disable remote management and restrict access to the router's web interface to trusted internal networks only
• Implement network segmentation to isolate affected devices from critical network resources
• Replace affected devices with currently supported router models that receive security updates

Patch Information

D-Link has discontinued support for the DIR-816 router series. No official patch will be released for CVE-2025-5620. The only effective remediation is to replace the affected device with a currently supported router model. For more information, visit the D-Link Official Website.

Additional technical details are available through VulDB #311106.

Workarounds

• Disable the web management interface entirely if not required for operations
• Block external access to the router's management interface (ports 80/443) using upstream firewall rules
• Implement access control lists (ACLs) to restrict management access to specific trusted IP addresses only
• Consider deploying a firewall in front of the vulnerable router to filter malicious requests to /goform/setipsec_config

# Example: Block external access to router management on upstream firewall
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP
# Allow management only from specific trusted admin workstation
iptables -I FORWARD -s <admin_ip> -d <router_ip> -p tcp --dport 80 -j ACCEPT