threat-modeling.md

Threat Model Analysis for phpoffice/phpspreadsheet

Threat: Malicious Formula Injection (File Parsing)

• Description: An attacker uploads a crafted spreadsheet file containing malicious formulas (e.g., =SYSTEM(), =WEBSERVICE()). PhpSpreadsheet parses the file, and if formula evaluation is enabled or occurs indirectly, the malicious formulas could be executed on the server.
• Impact: Remote Code Execution (RCE), Server Compromise, Data Breach, Privilege Escalation.
• PhpSpreadsheet Component Affected: Formula Parser, Calculation Engine (if enabled or indirectly triggered). Primarily affects file readers (e.g., XLSX Reader, CSV Reader, ODS Reader).
• Risk Severity: Critical
• Mitigation Strategies:
  • Disable Formula Calculation: If formula evaluation is not essential, disable it completely in PhpSpreadsheet configuration.
  • Input Validation and Sanitization: Implement strict file type validation and content checks to reject potentially malicious files.
  • Sandboxing: Run PhpSpreadsheet processing in a sandboxed environment with restricted permissions to limit the impact of potential RCE.
  • Regular Updates: Keep PhpSpreadsheet updated to the latest version to patch known vulnerabilities.

Threat: XML External Entity (XXE) Injection

• Description: An attacker uploads a malicious spreadsheet (XLSX, ODS) containing crafted XML that exploits XXE vulnerabilities in PhpSpreadsheet's XML parsing process. This can allow the attacker to read local files, perform Server-Side Request Forgery (SSRF), or cause Denial of Service.
• Impact: Information Disclosure (local file access), Server-Side Request Forgery (SSRF), Denial of Service (DoS).
• PhpSpreadsheet Component Affected: XML Readers (specifically used by XLSX and ODS Readers), potentially underlying XML processing libraries used by PHP.
• Risk Severity: High
• Mitigation Strategies:
  • Disable External Entity Processing: Configure PhpSpreadsheet and underlying XML libraries to disable external entity processing by default.
  • Regular Updates: Update PhpSpreadsheet and its dependencies to patch known XXE vulnerabilities.
  • Input Validation: Implement input validation to detect and reject suspicious XML structures in uploaded files.

Threat: Zip Bomb / Decompression Bomb

• Description: An attacker uploads a small, compressed spreadsheet file (XLSX, ODS) that expands to an enormous size when decompressed by PhpSpreadsheet. This can exhaust server resources (CPU, memory, disk space), leading to Denial of Service.
• Impact: Denial of Service (DoS), Resource Exhaustion, Application Unavailability.
• PhpSpreadsheet Component Affected: ZIP Archive Handling (used by XLSX and ODS Readers), File Readers (XLSX Reader, ODS Reader).
• Risk Severity: High
• Mitigation Strategies:
  • File Size Limits: Implement strict limits on the size of uploaded files.
  • Resource Limits: Set resource limits (memory, CPU time) for PhpSpreadsheet processing to prevent resource exhaustion.
  • Streaming/Iterative Parsing: If available in PhpSpreadsheet, use streaming or iterative parsing methods to limit memory usage during decompression and processing.

Threat: Buffer Overflow / Memory Corruption in Parsers

• Description: A malformed or excessively large spreadsheet file exploits bugs in PhpSpreadsheet's parsing logic (for any format: CSV, XLSX, ODS, etc.). This can lead to buffer overflows or memory corruption, potentially causing crashes, Denial of Service, or in severe cases, Remote Code Execution.
• Impact: Denial of Service (DoS), Application Crash, Potential Remote Code Execution (RCE).
• PhpSpreadsheet Component Affected: File Readers (CSV Reader, XLSX Reader, ODS Reader, etc.), Parsing Logic for specific file formats.
• Risk Severity: High (potentially Critical if RCE is possible)
• Mitigation Strategies:
  • Regular Updates: Keep PhpSpreadsheet updated to benefit from bug fixes and security patches.
  • Fuzzing and Security Testing: Conduct fuzzing and security testing of PhpSpreadsheet integration with various file formats and malformed files.
  • Resource Limits: Implement resource limits to mitigate DoS from crashes.

Threat: Known Vulnerabilities in PhpSpreadsheet (Unpatched)

• Description: PhpSpreadsheet itself may contain undiscovered or unpatched security vulnerabilities. Attackers can exploit these vulnerabilities if the application uses a vulnerable version of PhpSpreadsheet.
• Impact: Varies depending on the vulnerability, could range from Denial of Service to Remote Code Execution.
• PhpSpreadsheet Component Affected: Core library code, various modules depending on the specific vulnerability.
• Risk Severity: Varies (can be Critical, High, or Medium depending on the vulnerability)
• Mitigation Strategies:
  • Regular Updates: Crucially, keep PhpSpreadsheet updated to the latest stable version. Monitor security advisories and release notes.
  • Vulnerability Scanning: Use static analysis tools and vulnerability scanners to identify potential weaknesses in the application's use of PhpSpreadsheet and its dependencies.

Threat: Vulnerabilities in PhpSpreadsheet Dependencies

• Description: PhpSpreadsheet relies on external libraries. Vulnerabilities in these dependencies can indirectly compromise applications using PhpSpreadsheet.
• Impact: Varies depending on the dependency vulnerability, could range from Denial of Service to Remote Code Execution.
• PhpSpreadsheet Component Affected: Indirectly affects the entire library through dependency chain.
• Risk Severity: Varies (can be Critical, High, or Medium depending on the dependency vulnerability)
• Mitigation Strategies:
  • Dependency Management and Updates: Use dependency management tools (like Composer) to track and update PhpSpreadsheet and all its dependencies.
  • Dependency Vulnerability Scanning: Regularly scan dependencies for known vulnerabilities using security tools.
  • Monitor Security Advisories: Stay informed about security advisories for PhpSpreadsheet's dependencies.