CVE-2024-3739

Executive Summary

CVE-2024-3739 is a critical OS command injection vulnerability identified in cym1102 nginxWebUI, affecting versions up to and including 3.9.9. The flaw resides in the /adminPage/main/upload endpoint, where the file argument is improperly sanitized, allowing an authenticated attacker to inject arbitrary operating system commands. With a CVSS score of 6.3 (Medium), the vulnerability can be exploited remotely with low complexity and requires low privileges. Public exploit code has been disclosed, increasing the risk of active exploitation. No official patch is currently available, making immediate mitigation measures essential.

Supply Chain & Package Security

This vulnerability affects a Java-based web application (nginxWebUI) distributed via GitHub and potentially through other channels. As no official package manager (NPM, PyPI, Go, Ruby) is involved, supply chain risks are limited to the integrity of the source code repository and any pre-built binaries. Users should verify the authenticity of their downloaded artifacts and consider building from source after applying manual mitigations.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely over the network.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): Low (L) – Attacker needs a valid user account.
• User Interaction (UI): None (N) – No user action needed.
• Scope (S): Unchanged (U) – Impact confined to the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure possible.
• Integrity (I): Low (L) – Limited ability to modify data.
• Availability (A): Low (L) – Limited impact on service availability.

Threat Level: Medium. The combination of public exploit availability, low attack complexity, and remote exploitability elevates the risk despite the medium CVSS score.

Deep Dive & Mechanics

The vulnerability is an OS command injection in the file upload functionality of nginxWebUI. The application fails to properly sanitize user-supplied input in the file parameter of the /adminPage/main/upload endpoint. When processing the uploaded file, the application constructs a system command using unsanitized input, allowing an attacker to inject arbitrary commands.

Root Cause: The application likely uses a function like Runtime.exec() or ProcessBuilder in Java to execute system commands (e.g., for file processing or validation) without proper input validation or escaping. The file parameter is concatenated directly into the command string.

Attack Vector: An authenticated attacker sends a crafted HTTP POST request to /adminPage/main/upload with a malicious file parameter containing command injection payloads (e.g., ; id or | whoami). The injected command is executed on the server with the privileges of the nginxWebUI application.

Impact: Successful exploitation allows the attacker to execute arbitrary OS commands, potentially leading to data exfiltration, lateral movement, or full server compromise.

Vulnerable vs. Patched Code

Vulnerable Code (Conceptual):

// Vulnerable: Direct concatenation of user input into command
String fileName = request.getParameter("file");
String command = "some_tool --process " + fileName;
Runtime.getRuntime().exec(command);

Patched Code (Conceptual):

// Patched: Use of parameterized commands and input validation
String fileName = request.getParameter("file");
if (!isValidFileName(fileName)) {
    throw new SecurityException("Invalid file name");
}
List<String> command = Arrays.asList("some_tool", "--process", fileName);
ProcessBuilder pb = new ProcessBuilder(command);
pb.start();

Note: No official patch is available. The above is a recommended fix.

Exploitation & Lab Setup

Red Team

Prerequisites:

• A valid user account on the target nginxWebUI instance.
• Network access to the /adminPage/main/upload endpoint.

Exploit Steps:

1. Authenticate to the nginxWebUI application.
2. Craft a malicious HTTP POST request to /adminPage/main/upload with the file parameter containing a command injection payload.
3. Execute the request and observe the output.

Example Payload (using curl):

curl -X POST -u "username:password" \
  -F "file=;id" \
  http://target.com/adminPage/main/upload

Expected Output: The id command output will be reflected in the response or logged.

Blue Team

Detection:

• Monitor for unusual HTTP POST requests to /adminPage/main/upload with suspicious file parameters (e.g., containing shell metacharacters like ;, |, &, $).
• Analyze server logs for unexpected command execution events.
• Deploy WAF rules to block common command injection patterns.

Hunting:

• Search for processes spawned by the nginxWebUI Java process that are not typical (e.g., id, whoami, nc, bash).
• Review file upload logs for anomalous file names or sizes.

Indicators of Compromise (IOCs)

• Network:
  • HTTP POST requests to /adminPage/main/upload with file parameter containing shell metacharacters.
  • Outbound connections from the server to unknown IPs (potential C2).
• Host:
  • Unexpected processes running under the nginxWebUI user (e.g., id, whoami, curl, wget).
  • New files in /tmp or other writable directories.
  • Modified system binaries or configuration files.
• Logs:
  • Application logs showing command execution errors or unexpected output.
  • System logs (e.g., /var/log/syslog) with entries from the nginxWebUI process executing shell commands.

Detection Engineering

YARA Rule

rule CVE_2024_3739_Command_Injection {
    meta:
        description = "Detects command injection attempts targeting CVE-2024-3739 in nginxWebUI"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-3739"
    strings:
        $s1 = "/adminPage/main/upload" ascii wide nocase
        $s2 = "file=" ascii wide nocase
        $s3 = ";" ascii wide
        $s4 = "|" ascii wide
        $s5 = "`" ascii wide
        $s6 = "$(" ascii wide
    condition:
        $s1 and $s2 and any of ($s3, $s4, $s5, $s6)
}

Sigma Rule

title: CVE-2024-3739 Command Injection Attempt
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects HTTP POST requests to /adminPage/main/upload with command injection patterns
author: Valters IT
date: 2024-01-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: '/adminPage/main/upload'
        cs-uri-query|contains|all:
            - 'file='
            - ';'
    condition: selection
falsepositives:
    - Legitimate use of semicolons in file names (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (
    msg:"CVE-2024-3739 Command Injection Attempt";
    flow:to_server,established;
    content:"POST"; http_method;
    content:"/adminPage/main/upload"; http_uri;
    content:"file="; http_client_body;
    pcre:"/file=[^&]*(;|\||`|\$\(|&&)/Pi";
    sid:1000001;
    rev:1;
    reference:cve,2024-3739;
    classtype:attempted-admin;
    priority:1;
)

Remediation & Mitigation

Immediate Actions:

1. Disable the upload functionality if not required, by removing or restricting access to the /adminPage/main/upload endpoint.
2. Apply input validation – Implement strict whitelisting for file names (e.g., alphanumeric characters only) and reject any input containing shell metacharacters.
3. Use parameterized commands – Replace Runtime.exec() with ProcessBuilder and pass arguments as a list to prevent injection.
4. Restrict application privileges – Run nginxWebUI with the least privileges necessary (e.g., a dedicated low-privilege user).
5. Deploy a WAF – Use a web application firewall to block common command injection patterns.

Long-Term Fix:

• Monitor the vendor’s repository for an official patch. If none is forthcoming, consider forking the project and applying the fixes manually, or migrating to an alternative solution.

Valters IT Signature: This report was generated by Valters IT – DevSecOps & Cyber Threat Intelligence Division.