threat-modeling.md

Threat Model Analysis for phpoffice/phppresentation

Threat: XML External Entity (XXE) Injection in ODP/PPTX Parsing

• Description: An attacker crafts a malicious ODP or PPTX file (or provides malicious XML input if the application allows direct XML input) containing external entity references. These references could point to local files on the server, internal network resources, or external URLs. PHPPresentation, when parsing the XML within the ODP/PPTX structure, might resolve these entities, leading to information disclosure or potentially Server-Side Request Forgery (SSRF). This is a direct vulnerability within PHPPresentation's parsing logic.
  • Impact:
    • Information Disclosure: Exposure of sensitive files on the server (e.g., /etc/passwd, configuration files).
    • SSRF: The attacker could force the server to make requests to internal or external systems, potentially bypassing firewalls or accessing internal services.
    • Denial of Service: XXE can also be used for DoS attacks (e.g., the "Billion Laughs" attack).
  • PHPPresentation Component Affected:
    • PhpPresentation\Reader\Odf (for ODP files)
    • PhpPresentation\Reader\PowerPoint2007 (for PPTX files)
    • Any component that uses PHPPresentation's XML parsing capabilities internally (even if not directly exposed to user input, vulnerabilities in the parsing of the presentation structure are relevant).
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Disable External Entity Loading: The most effective mitigation is to completely disable the loading of external entities in the XML parser. This must be done at the level of the underlying XML library used by PHPPresentation (e.g., libxml_disable_entity_loader(true) in PHP, or equivalent configuration for other XML parsers). Verify that PHPPresentation is configured to do this, and test thoroughly. Do not assume it's handled by default.
    • Input Validation (Secondary): If user-provided XML is absolutely unavoidable (which is highly discouraged), implement strict validation against a predefined, known-good schema (whitelist approach). Do not rely on blacklisting. This is a secondary defense and should not be relied upon as the primary mitigation.
    • Update Dependencies: Ensure that PHPPresentation and its underlying XML parsing libraries are up-to-date to benefit from any security patches. This is crucial, as XXE vulnerabilities are often patched in underlying libraries.

Threat: Image File Inclusion Leading to Remote Code Execution (RCE) via PHPPresentation's Handling

• Description: While RCE through image processing is often attributed to underlying libraries (GD, Imagick), PHPPresentation's handling of image files and its interaction with these libraries is the direct point of concern. An attacker uploads a specially crafted image file that, when processed by PHPPresentation, triggers a vulnerability. The vulnerability might be in how PHPPresentation passes data to the underlying library, or in how it handles the results. The key is that PHPPresentation is the active component in the attack chain.
  • Impact:
    • Remote Code Execution (RCE): Complete compromise of the server, allowing the attacker to execute arbitrary commands, steal data, and potentially pivot to other systems.
  • PHPPresentation Component Affected:
    • PhpPresentation\Shape\Drawing\* (various classes for handling different image formats) – specifically, the code that interacts with external image processing libraries.
    • Any component that uses PHPPresentation's image handling capabilities and passes data to or receives data from external libraries.
  • Risk Severity: Critical
  • Mitigation Strategies:
    • Image Validation (Before PHPPresentation): Perform robust image validation before the image data is ever passed to PHPPresentation. Use a library that actually parses the image header and checks for structural integrity, not just file extensions.
    • Image Resizing/Re-encoding (Before PHPPresentation): Resize and re-encode all uploaded images using a trusted library (e.g., ImageMagick with a secure configuration) before passing them to PHPPresentation. This can mitigate many vulnerabilities in image parsing.
    • Update Dependencies: Keep PHPPresentation and all related image processing libraries (GD, Imagick, etc.) up-to-date. This is critical as many RCE vulnerabilities are patched in these libraries.
    • Least Privilege: Run the PHP process with limited privileges to minimize the impact of a successful RCE.
    • Sandboxing (Ideal): If possible, isolate the image processing component (including PHPPresentation's image handling) in a sandboxed environment (e.g., Docker, a separate process with restricted permissions).

Threat: Denial of Service via Resource Exhaustion (Complex Presentations) - PHPPresentation Processing

• Description: An attacker uploads a presentation file (or provides input that generates a presentation) designed to be excessively complex. This complexity directly targets PHPPresentation's parsing and rendering logic, causing it to consume excessive CPU, memory, or disk I/O, leading to a denial of service. The vulnerability lies in PHPPresentation's inability to efficiently handle such complex input.
  • Impact:
    • Denial of Service (DoS): The application becomes unresponsive, preventing legitimate users from accessing it.
  • PHPPresentation Component Affected:
    • All components involved in reading, parsing, and rendering presentations. This is a broad impact across the library, particularly affecting the core parsing and object model handling.
  • Risk Severity: High
  • Mitigation Strategies:
    • Input Validation (Targeted at PHPPresentation):
      • Limit the maximum file size of uploaded presentations before they are processed by PHPPresentation.
      • Limit the maximum number of slides, shapes, and other elements based on PHPPresentation's known limitations.
      • Limit the maximum dimensions and file sizes of embedded images before they are handled by PHPPresentation.
      • Restrict the nesting depth of objects within the presentation structure (if possible, and if PHPPresentation exposes such controls).
    • Resource Limits (PHP): Set resource limits (memory_limit, max_execution_time) for the PHP process specifically tailored to the expected resource usage of PHPPresentation.
    • Timeout Mechanisms (Application Level): Implement timeouts for presentation processing operations within your application code, wrapping calls to PHPPresentation.
    • Asynchronous Processing (Recommended): Use a queue system (e.g., RabbitMQ, Redis, Beanstalkd) to handle presentation generation asynchronously. This prevents a single malicious request from blocking the entire application and allows for better resource management.
    • Rate Limiting (Network/Application Level): Limit the number of presentation generation requests from a single user or IP address within a given time period.

Threat: Path Traversal in PHPPresentation's File Handling

• Description: If PHPPresentation allows specifying file paths for resources (images, templates, etc.) and PHPPresentation itself does not properly sanitize these paths, an attacker might use ".." sequences to access files outside the intended directory. This is a direct vulnerability in how PHPPresentation handles file paths internally.
  • Impact:
    • Information Disclosure: Reading arbitrary files on the server.
    • Potentially Code Execution: If the attacker can overwrite critical files (less likely, but possible depending on server configuration).
  • PHPPresentation Component Affected:
    • Any component that handles file paths internally, particularly within PhpPresentation\Shape\Drawing\* (for image loading) and potentially in any template loading mechanisms. The key is to identify where PHPPresentation itself constructs or manipulates file paths.
  • Risk Severity: High
  • Mitigation Strategies:
    • Strict Path Validation (Within Application, Before PHPPresentation): Validate all file paths provided to PHPPresentation before they are used. Use a whitelist of allowed directories and ensure that paths do not contain ".." sequences or other potentially dangerous characters. Use PHP's realpath() function (with caution, understanding its limitations and potential security implications if misused) or, preferably, a dedicated path sanitization library. The goal is to ensure that PHPPresentation never receives a potentially malicious path.
    • Avoid User-Controlled Paths (Ideal): If possible, avoid allowing users to directly specify file paths. Instead, use predefined paths or identifiers that map to safe locations.
    • Chroot Jail (Advanced): In highly sensitive environments, consider running the PHP process in a chroot jail to restrict its access to a specific directory subtree. This provides a strong layer of defense, but requires careful configuration.