CVE-2026-2168: D-Link DWR-M921 Firmware RCE Vulnerability

CVE-2026-2168 Overview

A command injection vulnerability has been identified in D-Link DWR-M921 firmware version 1.1.50. This flaw affects the function sub_419920 within the file /boafrm/formLtefotaUpgradeQuectel. By manipulating the fota_url argument, an authenticated attacker can inject arbitrary operating system commands that are executed on the vulnerable device. The attack can be initiated remotely over the network, making this vulnerability particularly concerning for internet-exposed devices.

Critical Impact

Remote attackers with low-level privileges can execute arbitrary commands on vulnerable D-Link DWR-M921 routers, potentially leading to full device compromise, network infiltration, and persistent backdoor access.

Affected Products

• D-Link DWR-M921 Firmware version 1.1.50
• D-Link DWR-M921 Hardware

Discovery Timeline

• 2026-02-08 - CVE-2026-2168 published to NVD
• 2026-02-11 - Last updated in NVD database

Technical Details for CVE-2026-2168

Vulnerability Analysis

This vulnerability represents a classic command injection flaw (CWE-77) combined with improper neutralization of special elements (CWE-74). The vulnerable function sub_419920 processes user-supplied input through the fota_url parameter without adequate sanitization or validation. When a user submits data to the /boafrm/formLtefotaUpgradeQuectel endpoint, the firmware fails to properly escape or filter shell metacharacters, allowing attackers to break out of the intended command context and execute arbitrary system commands.

The vulnerability is accessible remotely over the network and requires only low-level authentication privileges. An exploit for this vulnerability has been published and may be actively used, increasing the risk profile for unpatched devices.

Root Cause

The root cause stems from insufficient input validation in the FOTA (Firmware Over-The-Air) upgrade functionality. The fota_url parameter is passed directly or with minimal filtering to a system command execution context. The firmware developers failed to implement proper input sanitization techniques such as allowlisting valid characters, escaping shell metacharacters, or using parameterized command execution methods that prevent injection attacks.

Attack Vector

The attack is executed remotely over the network against the device's web management interface. An attacker with low-level authentication credentials can craft a malicious HTTP request to the /boafrm/formLtefotaUpgradeQuectel endpoint, including command injection payloads within the fota_url parameter. Common injection techniques include using shell metacharacters such as semicolons (;), pipes (|), backticks, or command substitution syntax to append malicious commands.

The vulnerability allows attackers to execute commands with the privileges of the web server process, which often runs as root on embedded devices. This could enable activities such as modifying device configuration, establishing reverse shells, exfiltrating sensitive data, or pivoting to attack other network resources.

For detailed technical analysis and proof-of-concept information, refer to the GitHub Issue Discussion and VulDB Entry #344870.

Detection Methods for CVE-2026-2168

Indicators of Compromise

• Unusual outbound connections from the D-Link DWR-M921 device to unknown IP addresses or command-and-control servers
• Unexpected processes running on the device that are not part of normal firmware operations
• Modified system files or configuration changes that were not authorized by administrators
• HTTP requests to /boafrm/formLtefotaUpgradeQuectel containing shell metacharacters or encoded command sequences

Detection Strategies

• Monitor web server access logs for requests to /boafrm/formLtefotaUpgradeQuectel with suspicious fota_url parameter values containing shell metacharacters
• Deploy network intrusion detection rules to identify command injection payloads in HTTP traffic destined for D-Link device management interfaces
• Implement anomaly detection for unusual network traffic patterns originating from router devices, including unexpected DNS queries or connections to external hosts

Monitoring Recommendations

• Enable verbose logging on the D-Link DWR-M921 device if available, and forward logs to a centralized SIEM for analysis
• Regularly audit device configurations and compare against known-good baselines to detect unauthorized modifications
• Monitor for firmware integrity changes or unexpected file modifications on the device

How to Mitigate CVE-2026-2168

Immediate Actions Required

• Restrict access to the device's web management interface to trusted internal networks only, blocking external access via firewall rules
• Implement strong authentication credentials and disable any default or weak accounts on the device
• Consider placing the affected device behind a VPN to limit exposure while awaiting a vendor patch
• If the device is not critical, consider disconnecting it from the network until a security update is available

Patch Information

At the time of publication, no official patch information has been released by D-Link for this vulnerability. Administrators should monitor the D-Link Security Information page for security advisories and firmware updates addressing CVE-2026-2168.

For additional technical details, refer to the VulDB Entry #344870 and the VulDB Submission #748838.

Workarounds

• Disable remote management access to the device's web interface from the WAN side
• Implement network segmentation to isolate the vulnerable device from critical network assets
• Deploy a web application firewall (WAF) or reverse proxy in front of the management interface to filter malicious requests containing command injection patterns
• If the FOTA upgrade functionality is not required, investigate whether it can be disabled through device configuration

# Example firewall rule to restrict management interface access (adjust for your environment)
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP