CVE-2025-1608: LB-LINK AC1900 Firmware RCE Vulnerability

CVE-2025-1608 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_manpwd endpoint. By manipulating the routepwd argument, an authenticated attacker can inject arbitrary operating system commands that execute with elevated privileges on the affected device. The exploit has been publicly disclosed, and the vendor was contacted but did not respond.

Critical Impact

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

Affected Products

• LB-LINK AC1900 Firmware version 1.0.2
• LB-LINK AC1900 Hardware

Discovery Timeline

• 2025-02-24 - CVE-2025-1608 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2025-1608

Vulnerability Analysis

This vulnerability is classified as an OS Command Injection flaw (CWE-78) with elements of Command Injection (CWE-77). The vulnerable endpoint /goform/set_manpwd is designed to handle password management functionality on the router's administrative interface. The websGetVar function processes user-supplied input from the routepwd parameter without proper sanitization or validation before passing it to system command execution functions.

The attack can be launched remotely over the network, requiring only low-level authentication. When exploited successfully, an attacker gains the ability to execute arbitrary commands within the context of the router's operating system, which typically runs with root privileges on embedded devices like consumer routers.

Root Cause

The root cause of this vulnerability is improper input validation in the websGetVar function. User-controlled input from the routepwd parameter is directly incorporated into OS command strings without adequate sanitization, escaping, or parameterization. This allows attackers to break out of the intended command context and inject additional commands using shell metacharacters such as semicolons, pipes, or backticks.

Attack Vector

The attack vector is network-based, targeting the router's web management interface at the /goform/set_manpwd endpoint. An attacker with valid credentials (even low-privilege access) can craft a malicious HTTP request containing command injection payloads in the routepwd parameter. The injected commands are then executed by the underlying system shell (bl_do_system function), allowing the attacker to:

• Execute arbitrary system commands with elevated privileges
• Exfiltrate sensitive configuration data including WiFi credentials
• Establish persistent backdoor access
• Pivot to attack other devices on the network
• Modify router configuration to redirect traffic

The vulnerability leverages inadequate input handling where special characters and shell metacharacters in the password field are processed as command delimiters rather than literal strings. For detailed technical analysis, refer to the VulDB advisory and the technical writeup.

Detection Methods for CVE-2025-1608

Indicators of Compromise

• Unusual HTTP POST requests to /goform/set_manpwd containing shell metacharacters (;, |, $(), backticks) in the routepwd parameter
• Unexpected outbound network connections from the router to external IP addresses
• New or modified files in router filesystem directories, particularly scripts or binaries
• Unusual processes running on the router device that are not part of standard firmware

Detection Strategies

• Deploy network monitoring to inspect HTTP traffic destined for router management interfaces, flagging requests with suspicious payloads in form parameters
• Implement Web Application Firewall (WAF) rules to detect and block common command injection patterns in POST requests
• Monitor router system logs for unexpected command executions or authentication anomalies
• Use intrusion detection signatures targeting command injection attempts against embedded device web interfaces

Monitoring Recommendations

• Enable logging on the router management interface to capture all administrative access attempts and configuration changes
• Implement network segmentation to isolate router management interfaces from untrusted network segments
• Deploy network flow analysis to detect unusual traffic patterns originating from network infrastructure devices
• Consider periodic firmware integrity verification if supported by the device

How to Mitigate CVE-2025-1608

Immediate Actions Required

• Restrict access to the router's web management interface by implementing IP-based access controls, limiting administration to trusted management stations only
• Disable remote management access from WAN interfaces if not strictly required
• Place the router management interface behind a VPN or jump host to prevent direct exposure
• Monitor the router for signs of compromise and consider factory reset if suspicious activity is detected

Patch Information

No official security patch is currently available from LB-LINK. The vendor was contacted about this vulnerability disclosure but did not respond. Affected organizations should implement compensating controls and consider device replacement with a supported alternative. Monitor the VulDB entry for any future updates regarding vendor response or patch availability.

Workarounds

• Implement strict network access controls using firewalls to limit which IP addresses can reach the router's management interface on port 80/443
• Disable HTTP/HTTPS management interface entirely if command-line or alternative management options are available
• Deploy a reverse proxy or WAF in front of the management interface to filter malicious requests containing command injection patterns
• Consider replacing the affected device with a router from a vendor that provides active security support and timely patches

# Configuration example - Restrict management access via iptables on upstream firewall
# Block external access to router management interface
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 443 -j DROP

# Allow only specific management station
iptables -I FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT
iptables -I FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 443 -j ACCEPT