CVE-2024-0921: D-Link DIR-816 A2 RCE Vulnerability

CVE-2024-0921 Overview

A critical OS command injection vulnerability has been discovered in D-Link DIR-816 A2 firmware version 1.10CNB04. This vulnerability exists within the Web Interface component, specifically in the /goform/setDeviceSettings endpoint. The flaw allows remote attackers to inject arbitrary operating system commands through manipulation of the statuscheckpppoeuser argument, potentially leading to complete device compromise.

Critical Impact

This vulnerability allows unauthenticated remote attackers to execute arbitrary OS commands on affected D-Link routers, potentially enabling full device takeover, network pivoting, and persistent access to internal networks.

Affected Products

• D-Link DIR-816 A2 Firmware version 1.10CNB04
• D-Link DIR-816 A2 Hardware

Discovery Timeline

• January 26, 2024 - CVE-2024-0921 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2024-0921

Vulnerability Analysis

This vulnerability is classified as CWE-78 (Improper Neutralization of Special Elements used in an OS Command), commonly known as OS Command Injection. The flaw resides in the web interface's device settings functionality, where user-supplied input in the statuscheckpppoeuser parameter is passed directly to system shell commands without proper sanitization or validation.

The vulnerable endpoint /goform/setDeviceSettings is accessible through the router's web management interface. When processing PPPoE (Point-to-Point Protocol over Ethernet) configuration requests, the firmware fails to sanitize special characters and shell metacharacters in the statuscheckpppoeuser argument. This allows attackers to append malicious commands that execute with the privileges of the web server process, typically root on embedded devices.

The exploit has been publicly disclosed and documented, significantly increasing the risk of active exploitation. Given that router firmware typically runs with elevated privileges, successful exploitation grants attackers complete control over the device.

Root Cause

The root cause of this vulnerability is insufficient input validation in the D-Link DIR-816 A2 firmware's web interface. The statuscheckpppoeuser parameter value is concatenated directly into a shell command string without proper sanitization, escaping, or validation. This design flaw allows shell metacharacters such as semicolons, pipes, and backticks to break out of the intended command context and execute attacker-controlled commands.

Attack Vector

The attack can be launched remotely over the network against the router's web management interface. An attacker with network access to the device's management port can craft malicious HTTP requests containing shell commands within the statuscheckpppoeuser parameter. Since the vulnerability requires no authentication and no user interaction, attackers can fully compromise vulnerable devices through automated attacks.

The vulnerability mechanism involves injecting shell metacharacters into the statuscheckpppoeuser parameter sent to the /goform/setDeviceSettings endpoint. When the firmware processes this request, the unsanitized input is passed to a shell execution function, allowing the injected commands to execute with elevated privileges. For detailed technical analysis and exploitation specifics, refer to the GitHub RCE Exploit Details.

Detection Methods for CVE-2024-0921

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/setDeviceSettings containing shell metacharacters (;, |, $(), backticks)
• Unusual outbound connections from the router to unknown external IP addresses
• Modifications to router configuration files or firmware settings not initiated by administrators
• Presence of unexpected processes running on the device, particularly reverse shells or download utilities

Detection Strategies

• Monitor HTTP traffic to the router's web interface for requests containing command injection patterns in the statuscheckpppoeuser parameter
• Implement network intrusion detection rules to alert on POST requests to /goform/setDeviceSettings with suspicious payloads
• Deploy behavioral monitoring to detect anomalous outbound connections originating from network edge devices
• Regularly audit router configurations for unauthorized changes

Monitoring Recommendations

• Enable logging on network firewalls to capture all traffic to and from router management interfaces
• Restrict management interface access to trusted internal networks only using firewall rules
• Implement network segmentation to isolate IoT and network infrastructure devices from general user networks
• Consider using a dedicated management VLAN with strict access controls for all network devices

How to Mitigate CVE-2024-0921

Immediate Actions Required

• Immediately restrict access to the router's web management interface from untrusted networks by configuring firewall rules
• Disable remote management if not strictly required for operations
• Isolate affected devices on a separate network segment until patched or replaced
• Monitor network traffic for signs of exploitation attempts or compromise
• Consider replacing end-of-life devices with actively supported models

Patch Information

At the time of publication, no vendor advisory or official patch has been released by D-Link for this vulnerability. Administrators should monitor the VulDB entry and D-Link's official security advisories for updates. Given D-Link's history of discontinuing support for older router models, affected organizations should evaluate whether replacement with a currently supported device is the most appropriate remediation strategy.

Workarounds

• Disable the web management interface entirely if not operationally required
• Implement strict network access controls to limit management interface access to specific administrator IP addresses only
• Deploy a web application firewall (WAF) or intrusion prevention system (IPS) with rules to block command injection patterns targeting the affected endpoint
• Use VPN access for remote management rather than exposing the management interface directly

# Example iptables rules to restrict management access
# Allow management access only from trusted admin subnet
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP