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Threat Model Analysis for mozilla/pdf.js

Threat: PDF Parsing Vulnerability Exploitation

  • Description: An attacker crafts a malicious PDF file with malformed or unexpected structures specifically designed to exploit weaknesses in pdf.js's PDF parsing logic. When a user opens this PDF in the application using pdf.js, the parser attempts to process the malicious structures, potentially leading to crashes, memory corruption, or in rare cases, code execution. The attacker might distribute this malicious PDF through various channels, such as email attachments, compromised websites, or file sharing platforms, aiming to target users of applications utilizing vulnerable pdf.js versions.
    • Impact:
      • Denial of Service (DoS) - Browser tab or browser crash, disrupting user access to the application and potentially other browser functionalities.
      • Potential Remote Code Execution (RCE) - Though less likely due to browser sandboxing, successful exploitation could allow an attacker to execute arbitrary code on the user's machine, leading to complete system compromise.
      • Information Disclosure - Parsing errors could lead to the leakage of sensitive data from the PDF content itself or potentially from browser memory, exposing confidential information to the attacker.
    • Affected pdf.js Component: PDF Parser (specifically modules responsible for parsing various PDF object types and structures, including but not limited to object streams, cross-reference tables, and content streams).
    • Risk Severity: High
    • Mitigation Strategies:
      • Keep pdf.js updated: Regularly update pdf.js to the latest stable version to benefit from crucial security patches and bug fixes that address known parsing vulnerabilities.
      • Implement robust error handling: Develop application-level error handling to gracefully manage potential parsing failures and prevent crashes from propagating to the entire application or browser.
      • Utilize browser sandboxing: Rely on the browser's built-in sandboxing mechanisms to limit the impact of potential RCE vulnerabilities by isolating pdf.js execution and restricting access to system resources.
      • Consider server-side PDF sanitization (if applicable): If your application workflow allows, implement server-side PDF sanitization or pre-processing to detect and potentially neutralize malicious PDF structures before they are processed by pdf.js in the user's browser. This adds an extra layer of defense.

Threat: Malicious JavaScript Execution in PDF

  • Description: An attacker embeds malicious JavaScript code within a PDF document. If pdf.js fails to properly sanitize, disable, or sandbox this JavaScript, it could be executed within the user's browser when the PDF is rendered. This malicious JavaScript can then operate within the context of the web application, potentially bypassing security measures and gaining unauthorized access. Attackers might use social engineering to trick users into opening PDFs containing malicious JavaScript, or embed them on compromised websites.
    • Impact:
      • Cross-Site Scripting (XSS) - Successful JavaScript execution can lead to XSS attacks, allowing the attacker to steal user cookies, session tokens, and potentially gain control of the user's account within the web application. They could also perform actions on behalf of the user without their knowledge or consent.
      • Information Disclosure - Malicious JavaScript could access browser APIs or local storage to steal sensitive user data, including personal information, financial details, or application-specific secrets.
      • Redirection/Phishing - The attacker could use JavaScript to redirect users to attacker-controlled websites, potentially for phishing attacks to steal credentials or install malware. They could also display fake login forms or misleading content within the PDF viewer to deceive users.
    • Affected pdf.js Component: JavaScript Engine/Sandbox (specifically modules responsible for handling and restricting JavaScript execution within PDFs, including the security policies and execution environment for embedded scripts).
    • Risk Severity: High
    • Mitigation Strategies:
      • Disable JavaScript execution in pdf.js (recommended): If your application's functionality does not require JavaScript execution within PDFs, configure pdf.js to completely disable this feature. This is the most effective mitigation.
      • Implement a strong Content Security Policy (CSP): Deploy a robust CSP for your web application to further restrict the capabilities of any JavaScript that might be executed by pdf.js, even if it bypasses initial sanitization. CSP can limit access to resources, APIs, and execution contexts, reducing the potential impact of XSS.
      • Educate users about PDF risks: Inform users about the potential risks associated with opening PDFs from untrusted sources and advise them to be cautious when opening PDFs, especially from unknown senders or websites.
      • Regularly review pdf.js JavaScript handling configurations: Periodically review and audit your pdf.js configuration related to JavaScript handling to ensure it remains secure and aligned with your application's security requirements.