CVE-2026-2085: D-Link DWR-M921 Firmware RCE Vulnerability

CVE-2026-2085 Overview

A command injection vulnerability has been identified in the D-Link DWR-M921 mobile router firmware version 1.1.50. The vulnerability exists in the function sub_419F20 within the USSD Configuration Endpoint located at /boafrm/formUSSDSetup. An authenticated attacker with high privileges can exploit this vulnerability by manipulating the ussdValue argument to inject arbitrary operating system commands, potentially leading to complete device compromise.

Critical Impact

Remote command injection vulnerability allowing authenticated attackers to execute arbitrary system commands on the affected D-Link DWR-M921 router, potentially leading to full device takeover, network pivoting, and data exfiltration.

Affected Products

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

Discovery Timeline

• 2026-02-07 - CVE-2026-2085 published to NVD
• 2026-02-12 - Last updated in NVD database

Technical Details for CVE-2026-2085

Vulnerability Analysis

This vulnerability is classified as a command injection flaw (CWE-77) with an underlying injection weakness (CWE-74). The vulnerable function sub_419F20 processes user-supplied input from the ussdValue parameter without proper sanitization or validation. When a request is made to the /boafrm/formUSSDSetup endpoint, the parameter value is passed directly to system command execution routines, allowing attackers to append or inject malicious commands.

The vulnerability requires network access and high-level privileges to exploit, but once these prerequisites are met, an attacker can achieve high impact on confidentiality, integrity, and availability of the affected device. The exploit has been publicly disclosed, increasing the risk of active exploitation in the wild.

Root Cause

The root cause of this vulnerability is improper input validation in the USSD Configuration Endpoint. The ussdValue parameter is not adequately sanitized before being incorporated into system command execution contexts. This allows specially crafted 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.

Attack Vector

The attack is initiated remotely over the network through the device's web management interface. An authenticated attacker with administrative privileges can send a specially crafted HTTP request to the /boafrm/formUSSDSetup endpoint with a malicious ussdValue parameter. The injected commands execute in the context of the router's operating system, potentially allowing the attacker to:

• Gain persistent shell access to the device
• Modify device configuration
• Intercept or redirect network traffic
• Use the compromised device as a pivot point for lateral movement
• Extract sensitive information including credentials

The vulnerability mechanism involves improper handling of the ussdValue parameter in the USSD Configuration Endpoint. When processing this parameter, the application fails to sanitize special characters before passing the value to system command functions. For detailed technical analysis, refer to the GitHub Issue Discussion and VulDB entry.

Detection Methods for CVE-2026-2085

Indicators of Compromise

• Unusual HTTP requests to /boafrm/formUSSDSetup containing special characters like ;, |, &&, or backticks in the ussdValue parameter
• Unexpected outbound network connections originating from the router
• Unauthorized configuration changes on the D-Link DWR-M921 device
• Suspicious processes running on the router that are not part of normal firmware operation

Detection Strategies

• Implement network-level monitoring to detect HTTP requests targeting /boafrm/formUSSDSetup with anomalous parameter values
• Deploy intrusion detection rules to identify command injection patterns in web traffic destined for D-Link management interfaces
• Monitor authentication logs for unusual administrative access patterns followed by configuration endpoint access
• Utilize SentinelOne Singularity to detect post-exploitation behaviors on network endpoints that may indicate router compromise

Monitoring Recommendations

• Enable and regularly review access logs on the D-Link DWR-M921 web management interface
• Implement network segmentation to limit management interface exposure and facilitate anomaly detection
• Deploy network traffic analysis tools to baseline normal router behavior and alert on deviations
• Consider implementing a Web Application Firewall (WAF) to filter malicious requests to router management interfaces

How to Mitigate CVE-2026-2085

Immediate Actions Required

• Restrict access to the D-Link DWR-M921 management interface to trusted IP addresses only
• Ensure the management interface is not exposed to the public internet
• Change default administrative credentials and use strong, unique passwords
• Review administrative user accounts and remove any unnecessary privileged access
• Monitor for firmware updates from D-Link and apply patches when available

Patch Information

At the time of publication, no official patch information has been released by D-Link. Administrators should monitor the D-Link Official Website for security advisories and firmware updates addressing CVE-2026-2085. The vulnerability details have been documented in VulDB #344652.

Workarounds

• Implement access control lists (ACLs) to restrict management interface access to specific trusted IP addresses
• Place the router management interface behind a VPN to prevent direct internet exposure
• Consider network segmentation to isolate the affected device from critical network assets
• Disable the USSD Configuration feature if it is not required for your deployment

# Example: Restrict management access using firewall rules (external firewall)
# Block external access to the router management interface
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 access only from trusted admin network
iptables -I FORWARD -s <trusted_network>/24 -d <router_ip> -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s <trusted_network>/24 -d <router_ip> -p tcp --dport 443 -j ACCEPT