CVE-2025-1609: LB-LINK AC1900 Firmware RCE Vulnerability

CVE-2025-1609 Overview

A critical OS command injection vulnerability has been identified in the LB-LINK AC1900 Router firmware version 1.0.2. The vulnerability exists in the websGetVar function within the /goform/set_cmd endpoint, allowing remote authenticated attackers to inject and execute arbitrary operating system commands on the affected device. The exploit has been publicly disclosed, and the vendor was contacted about this issue but did not respond.

Critical Impact

Remote attackers with low-level privileges can execute arbitrary commands on vulnerable LB-LINK AC1900 routers, potentially leading to complete device compromise, network infiltration, and persistent backdoor installation.

Affected Products

• LB-LINK AC1900 Firmware version 1.0.2
• LB-LINK AC1900 Router hardware

Discovery Timeline

• 2025-02-24 - CVE-2025-1609 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2025-1609

Vulnerability Analysis

This vulnerability is classified as an OS Command Injection (CWE-78) and Command Injection (CWE-77) flaw affecting the LB-LINK AC1900 router's web management interface. The vulnerable function websGetVar fails to properly sanitize user-supplied input in the cmd argument before passing it to system command execution routines.

The attack surface is network-accessible, requiring only low-level authentication privileges to exploit. The flaw resides in the /goform/set_cmd endpoint, which is designed to handle configuration commands but lacks adequate input validation. When an attacker supplies malicious input containing shell metacharacters or command separators, the router's underlying operating system interprets and executes the injected commands with the privileges of the web server process.

Root Cause

The root cause of this vulnerability is improper input validation in the websGetVar function within the /goform/set_cmd form handler. The function directly processes the cmd parameter without sanitizing special characters such as semicolons, pipes, backticks, or other shell metacharacters. This allows attackers to break out of the intended command context and inject arbitrary commands that execute on the router's operating system.

Attack Vector

The attack is network-based and can be launched remotely by any authenticated user with access to the router's web management interface. An attacker would craft a malicious HTTP request to the /goform/set_cmd endpoint, embedding OS commands within the cmd parameter. Common injection techniques include using command separators (;, |, &&) or command substitution syntax (`command` or $(command)) to append malicious commands to legitimate operations.

The vulnerability allows attackers to execute commands that could dump credentials, modify system configurations, establish reverse shells, or pivot to other devices on the network. Given the router's position as a network gateway device, successful exploitation could provide attackers with strategic access to internal network resources.

Technical details and documentation are available in the Notion Command Set Documentation and VulDB #296599.

Detection Methods for CVE-2025-1609

Indicators of Compromise

• Unusual HTTP POST requests to /goform/set_cmd containing shell metacharacters (;, |, &&, $(, `)
• Unexpected outbound network connections from the router to external IP addresses
• Modified configuration files or creation of new user accounts on the router
• Presence of reverse shell processes or unusual command execution in router logs

Detection Strategies

• Monitor web server logs on the router for requests to /goform/set_cmd with suspicious cmd parameter values
• Deploy network intrusion detection rules to identify command injection patterns in HTTP traffic destined for router management interfaces
• Implement baseline monitoring for router behavior and alert on deviations such as new listening ports or outbound connections
• Review authentication logs for brute-force attempts or compromised credential usage on router admin interfaces

Monitoring Recommendations

• Enable verbose logging on the router's web management interface if available
• Configure SIEM rules to correlate HTTP requests to /goform/set_cmd with subsequent suspicious network activity
• Segment router management interfaces from general network traffic to limit exposure
• Regularly audit router configurations for unauthorized changes

How to Mitigate CVE-2025-1609

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses or management VLANs only
• Disable remote management access if not required for operations
• Change default credentials and enforce strong authentication on the router
• Consider replacing vulnerable devices with alternatives that receive active security support

Patch Information

No patch is currently available from the vendor. LB-LINK was contacted regarding this vulnerability but did not respond. Organizations should implement compensating controls and consider device replacement. Monitor the vendor's support channels and VulDB for any future updates.

Workarounds

• Implement firewall rules to restrict access to the /goform/set_cmd endpoint and other management interfaces
• Place the router behind a network access control solution that limits administrative access to authorized personnel
• Deploy a Web Application Firewall (WAF) or reverse proxy with command injection detection capabilities in front of the management interface
• Consider firmware alternatives or third-party firmware if compatible and available for the hardware

# Example: Restrict router management access via external firewall
# Block external access to router management port (commonly 80/443)
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