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attack-surface.md

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Attack Surface Analysis for phpoffice/phppresentation

Attack Surface: XML External Entity (XXE) Injection

  • Description: Exploitation of insecure XML parsing to access local files, perform SSRF, or cause DoS.
  • phpoffice/phppresentation Contribution: The library parses XML as part of the OOXML (PPTX) format. If the underlying XML parser is misconfigured, it becomes vulnerable. This is a direct involvement because the library's core functionality relies on XML parsing.
  • Example: An attacker uploads a PPTX file containing an XML entity that references a sensitive local file (e.g., /etc/passwd) or an internal service endpoint.
  • Impact:
    • Disclosure of sensitive local files.
    • Server-Side Request Forgery (SSRF) to internal or external systems.
    • Denial of Service (DoS).
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Developer:
      • Disable External Entity Resolution: Use libxml_disable_entity_loader(true); in PHP before any XML parsing operations related to the library. This is the primary defense and is absolutely essential.
      • Validate XML Schema (if feasible): If a strict schema is available, validate against it. This is a secondary, more complex defense.

Attack Surface: XML Bomb (Billion Laughs Attack)

  • Description: Denial of Service attack using exponentially expanding XML entities.
  • phpoffice/phppresentation Contribution: The library parses XML, making it susceptible to resource exhaustion if entity expansion isn't limited. This is direct involvement as the library's core functionality includes XML parsing.
  • Example: An attacker uploads a PPTX file with deeply nested XML entities that consume all available memory.
  • Impact: Denial of Service (DoS) due to resource exhaustion (CPU, memory).
  • Risk Severity: High
  • Mitigation Strategies:
    • Developer:
      • Limit XML Entity Expansion: Check if the underlying XML parser has built-in limits (and verify they are enabled). If not, implement application-level checks to limit recursion depth and overall entity expansion.
      • Limit File Size: Enforce a reasonable maximum file size for uploaded PPTX files. This is a general good practice and helps mitigate this specific attack.
      • Resource Monitoring: Monitor server resources (CPU, memory) during PPTX processing.

Attack Surface: Image/Media Parsing Vulnerabilities

  • Description: Exploitation of vulnerabilities in image/media parsing libraries used by phpoffice/phppresentation.
  • phpoffice/phppresentation Contribution: The library directly interacts with and relies on external image/media processing libraries (e.g., GD, ImageMagick) when handling embedded content within PPTX files. This is a direct involvement because the library's functionality includes processing these embedded resources.
  • Example: An attacker embeds a maliciously crafted image within a PPTX file, designed to trigger a buffer overflow in the image parsing library (e.g., a known vulnerability in an older version of GD).
  • Impact:
    • Remote Code Execution (RCE) (if the underlying library vulnerability allows it).
    • Denial of Service (DoS).
    • Information Disclosure.
  • Risk Severity: High (potentially Critical if RCE is possible)
  • Mitigation Strategies:
    • Developer:
      • Keep Libraries Updated: Ensure GD, ImageMagick, and any other image/media processing libraries are up-to-date with the latest security patches. This is crucial. Use composer update regularly and monitor for security advisories related to these libraries.
      • Input Validation (Image): Validate image dimensions, file sizes, and file types before passing them to the processing libraries. This can help prevent some exploits.
      • Sandboxing (Ideal): Process images in a sandboxed environment (e.g., a container) to limit the impact of any vulnerabilities. This is the most robust mitigation.

Attack Surface: Zip Slip Vulnerability

  • Description: Exploitation of insecure file extraction to write files outside the intended directory.
  • phpoffice/phppresentation Contribution: If the application extracts files from a ZIP archive (which PPTX files are) and uses those files with phpoffice/phppresentation, a vulnerability could exist. This is direct involvement, because phppresentation is working with extracted files.
  • Example: An attacker uploads a crafted PPTX file with a filename containing ".." sequences, causing files to be extracted to an unintended location on the server.
  • Impact:
    • Overwriting critical system files.
    • Remote Code Execution (RCE).
  • Risk Severity: High
  • Mitigation Strategies:
    • Developer:
      • Validate Filenames: Before extracting files, thoroughly validate filenames to ensure they don't contain directory traversal characters ("../", "..", etc.).
      • Use Secure Extraction Functions: Use secure file extraction functions that are designed to prevent Zip Slip vulnerabilities. Avoid custom extraction logic.
      • Least Privilege: Run the extraction process with the least necessary privileges.