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Mitigation Strategies Analysis for stirling-tools/stirling-pdf

Mitigation Strategy: Strict Timeouts (Stirling-PDF Operations)

Description:

  1. Identify Stirling-PDF API Calls: List all direct calls to Stirling-PDF functions within your application code (e.g., splitPDF(), mergePDF(), extractText(), performOCR(), and any others you use).
  2. Determine Reasonable Time Limits: For each Stirling-PDF function call, estimate a maximum reasonable processing time. This should be based on factors like expected file size ranges, complexity of operations, and server resources. Start conservatively and adjust based on testing.
  3. Implement Timeouts Around API Calls: Wrap each individual Stirling-PDF function call in a timeout mechanism provided by your programming language. If the Stirling-PDF operation exceeds the timeout, forcefully terminate the associated process or release the resources held by the Stirling-PDF library. This prevents a single, slow operation from blocking the entire application.
  4. Handle Timeout Exceptions: Implement robust error handling to catch timeout exceptions that occur when a Stirling-PDF operation is terminated. Log the event, handle the error gracefully, and prevent application crashes.
  5. Regularly review and adjust: Periodically review the timeout values and adjust them as needed based on performance monitoring and changes in the application or expected input.

Threats Mitigated:

  • Resource Exhaustion (Denial of Service) within Stirling-PDF: (Severity: High) - Prevents attackers from crafting malicious PDFs that cause specific Stirling-PDF operations (splitting, merging, OCR, etc.) to consume excessive CPU or memory, even if the overall file size is within limits.
  • Hanging Stirling-PDF Processes: (Severity: Medium) - Prevents the application from becoming unresponsive due to a Stirling-PDF operation getting stuck on a malformed or complex PDF.

Impact:

  • Resource Exhaustion: Significantly reduces the risk by limiting the time any single Stirling-PDF operation can consume.
  • Hanging Processes: Eliminates the risk of individual Stirling-PDF operations hanging indefinitely.

Currently Implemented:

  • Timeout for the extractText() function implemented using Python's concurrent.futures with a timeout of 30 seconds.

Missing Implementation:

  • Timeouts are missing for mergePDF() and performOCR() functions. These need to be added with appropriate timeout values.
  • No granular timeouts based on file size within the Stirling-PDF operation wrappers.

Mitigation Strategy: Disable JavaScript and Forms (PDFBox Configuration)

Description:

  1. Assess the Need: Determine if your application's use of Stirling-PDF requires JavaScript execution or form handling within the processed PDFs. If these features are not essential, disabling them significantly reduces the attack surface.
  2. Identify PDFBox Configuration Options: Stirling-PDF relies on PDFBox. Consult the PDFBox documentation to find the specific configuration options for disabling JavaScript and form execution. Common options include:
    • PDDocument.setJavaScript(null) (or equivalent to disable JavaScript)
    • Settings related to PDAcroForm to disable form filling and submission.
  3. Apply Configuration in Code: Modify your application code to apply these PDFBox configuration settings before passing the PDF document to Stirling-PDF for processing. This ensures that the underlying PDF parsing library operates with these security restrictions.
  4. Test Thoroughly: After implementing these changes, thoroughly test your application's functionality to ensure that core features are not broken and that PDFs are still processed as expected (without JavaScript or form execution).

Threats Mitigated:

  • Malicious PDF Content (Exploits via PDFBox): (Severity: High) - Eliminates a large category of PDF-based exploits that rely on malicious JavaScript or form actions to compromise the PDF parsing library (PDFBox) itself.

Impact:

  • Malicious PDF Content: Significantly reduces the risk of exploits targeting PDFBox, if JavaScript and forms are not required for your application's functionality.

Currently Implemented:

  • None.

Missing Implementation:

  • The application does not currently configure PDFBox to disable JavaScript or forms. This is a missing security measure that should be implemented if the application's functionality permits.

Mitigation Strategy: Configure Secure Temporary File Handling (Stirling-PDF/PDFBox)

Description:

  1. Identify Temporary File Usage: Determine how Stirling-PDF and, crucially, its underlying PDFBox library, create and manage temporary files during PDF processing. This may involve inspecting the Stirling-PDF and PDFBox source code or documentation.
  2. Configure a Dedicated Temporary Directory (if possible): If Stirling-PDF or PDFBox provides configuration options to specify a temporary directory, use this to set a dedicated, secure directory. This directory should:
    • Be located on a secure partition.
    • Have restricted permissions (only the user running the application should have access).
    • Be regularly cleaned up (e.g., via a separate process or system utility).
  3. Influence Temporary File Permissions (if possible): If Stirling-PDF or PDFBox allows control over the permissions of created temporary files, ensure they are set to the most restrictive settings possible (e.g., read/write only for the owning user). This might involve modifying Stirling-PDF's code if direct configuration options are not available.
  4. Secure Deletion (if control is possible): If you have any influence over how Stirling-PDF deletes temporary files (e.g., through callbacks or by modifying its source), ensure secure deletion methods are used that overwrite the file contents to prevent data recovery.

Threats Mitigated:

  • Data Leakage (from Stirling-PDF's temporary files): (Severity: Medium) - Reduces the risk of sensitive data from processed PDFs remaining in temporary files, where it could be accessed by unauthorized users or recovered.
  • Local File Inclusion (LFI) targeting Stirling-PDF: (Severity: Medium) - Makes it harder for attackers to exploit LFI vulnerabilities to access or manipulate Stirling-PDF's temporary files.

Impact:

  • Data Leakage: Reduces the risk of data exposure from temporary files created by Stirling-PDF.
  • LFI: Provides some mitigation, but other LFI defenses are also needed.

Currently Implemented:

  • The application relies on the default temporary file handling of Stirling-PDF and the underlying OS.

Missing Implementation:

  • No specific configuration of Stirling-PDF or PDFBox's temporary file handling is in place. This should be investigated to determine if any control is possible and, if so, to implement secure settings.

Mitigation Strategy: Limit OCR Usage (Stirling-PDF Feature Control)

Description:

  1. Assess OCR Necessity: Determine if OCR is essential for all PDF processing within your application. If not, provide mechanisms to control or limit its use.
  2. Provide a Disable Option: If OCR is not always required, offer a user-configurable option (e.g., a checkbox, an API parameter) to disable OCR processing for specific files or requests.
  3. Conditional OCR: Implement logic within your application to only invoke Stirling-PDF's OCR functionality when it's truly needed, based on file type, user input, or other criteria. Avoid unnecessary OCR processing.
  4. Separate OCR Processing: If possible, consider isolating OCR processing into a separate function or service within your application. This allows for more granular control over timeouts, resource limits, and error handling specifically for OCR.

Threats Mitigated:

  • Resource Exhaustion (Denial of Service) targeting OCR: (Severity: High) - Reduces the attack surface by allowing users or the application to disable OCR when it's not needed, preventing attackers from forcing expensive OCR operations on maliciously crafted images within PDFs.
  • Performance Issues: (Severity: Medium) - Improves overall application performance by avoiding unnecessary OCR processing, which is computationally intensive.

Impact:

  • Resource Exhaustion: Significantly reduces the risk if OCR can be selectively disabled or controlled.
  • Performance Issues: Improves performance by avoiding unnecessary OCR.

Currently Implemented:

  • OCR is automatically performed on all uploaded PDFs.

Missing Implementation:

  • No mechanism to disable or conditionally control OCR usage. This should be added to allow users or the application to avoid unnecessary OCR processing.