CVE-2025-55422

Executive Summary

CVE-2025-55422 identifies a reflected Cross-Site Scripting (XSS) vulnerability in FoxCMS version 1.2.6. The flaw exists in the /index.php/plus endpoint, allowing an attacker to inject arbitrary JavaScript code into a web page via a crafted request. This can lead to session hijacking, credential theft, or defacement. No official patch has been released, and the CVSS score is currently unassigned (0.0). The EPSS score is 0.0%, indicating low exploitation probability at this time, but the vulnerability is publicly known.

Supply Chain & Package Security

FoxCMS is a PHP-based content management system. This vulnerability is not related to any specific package manager (NPM, PyPI, Go, Ruby) but affects the core application. Users should verify the integrity of their FoxCMS installation and monitor for any third-party plugins that may be affected.

CVSS Breakdown & Threat Level

• CVSS Score: 0.0 (Unassigned)
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None
• User Interaction: Required
• Scope: Changed
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

Threat Level: Medium (due to public PoC and lack of patch)

Deep Dive & Mechanics

The vulnerability is a reflected XSS in the /index.php/plus endpoint. The application fails to properly sanitize user input before reflecting it back in the HTTP response. An attacker can craft a URL containing malicious JavaScript code. When a victim clicks on the link, the script executes in the context of the victim's browser, allowing the attacker to steal cookies, session tokens, or perform actions on behalf of the user.

Root Cause: Lack of output encoding or input validation on the plus parameter.

Vulnerable vs. Patched Code

Vulnerable Code (FoxCMS 1.2.6):

// index.php/plus endpoint
$plus = $_GET['plus'];
echo "You selected: " . $plus;

Patched Code (Hypothetical):

// index.php/plus endpoint
$plus = htmlspecialchars($_GET['plus'], ENT_QUOTES, 'UTF-8');
echo "You selected: " . $plus;

Exploitation & Lab Setup

Red Team

Proof of Concept (PoC):

http://target.com/index.php/plus?plus=<script>alert('XSS')</script>

Advanced Payload:

http://target.com/index.php/plus?plus=<img src=x onerror=alert(document.cookie)>

Lab Setup:

1. Install FoxCMS 1.2.6 on a local server (e.g., XAMPP, LAMP).
2. Navigate to the vulnerable endpoint with the PoC URL.
3. Observe the JavaScript execution.

Blue Team

Detection:

• Monitor web server logs for requests containing <script> or onerror patterns in the plus parameter.
• Use WAF rules to block suspicious query strings.

Mitigation:

• Apply input validation and output encoding.
• Use Content Security Policy (CSP) headers to restrict script execution.

Indicators of Compromise (IOCs)

• URL Pattern: /index.php/plus?plus=*<script>*
• Log Entry: GET /index.php/plus?plus=<script>alert('XSS')</script>
• Network Traffic: HTTP requests with plus parameter containing HTML/JavaScript tags.

Detection Engineering

YARA Rule

rule FoxCMS_XSS_Reflected {
    meta:
        description = "Detects reflected XSS attempts against FoxCMS /index.php/plus"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2025-55422"
    strings:
        $xss_pattern = /plus=.*<script[^>]*>.*<\/script>/i
        $xss_pattern2 = /plus=.*<img[^>]*onerror[^>]*>/i
    condition:
        any of them
}

Sigma Rule

title: FoxCMS Reflected XSS Detection
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects reflected XSS attempts against FoxCMS /index.php/plus
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: GET
        cs-uri-query|contains: 
            - 'plus=<script'
            - 'plus=<img'
            - 'plus=onerror'
    condition: selection
falsepositives:
    - Legitimate use of HTML in parameters (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"FoxCMS Reflected XSS Attempt"; flow:to_server; content:"GET"; http_method; content:"/index.php/plus"; http_uri; content:"plus="; http_uri; pcre:"/plus=.*<script[^>]*>.*<\/script>/i"; sid:1000001; rev:1;)

Remediation & Mitigation

1. Immediate: Apply input validation and output encoding to the plus parameter.
2. Short-term: Implement a Web Application Firewall (WAF) rule to block malicious payloads.
3. Long-term: Upgrade to a patched version of FoxCMS if available, or consider migrating to a supported CMS.
4. Monitoring: Enable logging and alerting for suspicious requests to /index.php/plus.

Valters IT Signature
This report is generated by Valters IT Cyber Threat Intelligence. For questions, contact intelligence@valtersit.com.