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Attack Tree Analysis for phpoffice/phpexcel

Objective: Compromise Application Using PHPExcel/PHPSpreadsheet Vulnerabilities

Attack Tree Visualization

Attack Goal: Compromise Application Using PHPSpreadsheet Vulnerabilities └───[OR]─> 1. Exploit File Parsing Vulnerabilities [HIGH RISK PATH] │ └───[OR]─> 1.1. Remote Code Execution (RCE) via Malicious File [CRITICAL NODE - RCE] │ │ └───[AND]─> 1.1.1. Identify File Parsing Vulnerability in PHPSpreadsheet [CRITICAL NODE - Vulnerability Identification] │ │ └───[AND]─> 1.1.1.1. Vulnerability in Format Reader (e.g., Excel, CSV, ODS) [CRITICAL NODE - Format Reader Vulnerability] │ │ └───[AND]─> 1.1.3. Upload/Provide Malicious File to Application │ │ └───[AND]─> 1.1.3.1. Application Allows File Upload │ │ └───[AND]─> 1.1.3.2. Application Processes Uploaded File with PHPSpreadsheet │ └───[OR]─> 1.2. Denial of Service (DoS) via Resource Exhaustion [HIGH RISK PATH] │ │ └───[AND]─> 1.2.1. Identify Resource Intensive Parsing Behavior │ │ └───[AND]─> 1.2.3. Upload/Provide Resource Exhausting File to Application │ │ └───[AND]─> 1.2.3.1. Application Allows File Upload │ │ └───[AND]─> 1.2.3.2. Application Processes Uploaded File with PHPSpreadsheet │ └───[OR]─> 1.3. Information Disclosure via File Parsing Errors/Exceptions │ │ └───[AND]─> 1.3.2. Application Exposes Error Messages to Attacker [CRITICAL NODE - Error Exposure] │ │ └───[AND]─> 1.3.2.1. Lack of Proper Error Handling in Application Code [CRITICAL NODE - Application Error Handling Flaw] │ │ └───[AND]─> 1.3.2.2. Debug Mode Enabled in Production [CRITICAL NODE - Debug Mode in Prod] └───[OR]─> 2. Exploit File Generation Vulnerabilities │ └───[OR]─> 2.1. Content Injection in Generated Files [CRITICAL NODE - Content Injection] │ │ └───[AND]─> 2.1.1. Application Logic Flaws in Data Handling [CRITICAL NODE - Input Sanitization Flaw] │ │ └───[AND]─> 2.1.2. PHPSpreadsheet Generates File with Injected Content │ │ └───[AND]─> 2.1.3. Attacker Gains Advantage from Injected Content │ └───[OR]─> 2.2. Formula Injection in Generated Files [CRITICAL NODE - Formula Injection] │ │ └───[AND]─> 2.2.1. Application Logic Flaws in Formula Generation [CRITICAL NODE - Formula Sanitization Flaw] │ │ └───[AND]─> 2.2.2. PHPSpreadsheet Generates File with Injected Formula │ │ └───[AND]─> 2.2.3. Recipient of File Executes Malicious Formula └───[OR]─> 3. Dependency Vulnerabilities │ └───[AND]─> 3.1. PHPSpreadsheet Relies on Vulnerable Dependencies [CRITICAL NODE - Dependency Vulnerability] │ │ └───[AND]─> 3.1.2. Discover Known Vulnerabilities in Dependencies │ │ └───[AND]─> 3.1.3. Exploit Vulnerability in Dependency Through PHPSpreadsheet Usage └───[OR]─> 4. Configuration/Usage Vulnerabilities │ └───[OR]─> 4.1. Unsafe Temporary File Handling [CRITICAL NODE - Insecure Temp File Handling] │ │ └───[AND]─> 4.1.2. Application Fails to Securely Manage Temporary Files [CRITICAL NODE - Application Temp File Management Flaw] │ └───[OR]─> 4.2. Insecure Deserialization [CRITICAL NODE - Insecure Deserialization] │ │ └───[AND]─> 4.2.2. Deserialization Process is Vulnerable [CRITICAL NODE - Vulnerable Deserialization Process]

Attack Tree Path: 1. Exploit File Parsing Vulnerabilities [HIGH RISK PATH]

  • 1.1. Remote Code Execution (RCE) via Malicious File [CRITICAL NODE - RCE]:

    • Attack Vector: Attacker crafts a malicious spreadsheet file designed to exploit a vulnerability in PHPSpreadsheet's file parsing process.
    • Vulnerability Focus:
      • 1.1.1.1. Vulnerability in Format Reader (e.g., Excel, CSV, ODS) [CRITICAL NODE - Format Reader Vulnerability]: Bugs within the code that reads and interprets different spreadsheet file formats. This could be due to:
        • Buffer overflows when handling unexpected data lengths.
        • Integer overflows leading to memory corruption.
        • Logic errors in parsing specific file structures.
    • Exploitation Steps:
      1. Identify Vulnerability: Discover a specific parsing flaw in PHPSpreadsheet's format readers.
      2. Craft Malicious File: Create a spreadsheet file that triggers the identified vulnerability. This might involve:
        • Embedding specific byte sequences or malformed data structures in the file.
        • Creating files that exceed expected size limits or structure complexity.
      3. Upload/Provide Malicious File: Get the application to process the crafted file, typically by uploading it through a file upload feature.
    • Impact: Successful exploitation leads to Remote Code Execution, allowing the attacker to gain complete control of the server.

  • 1.2. Denial of Service (DoS) via Resource Exhaustion [HIGH RISK PATH]:

    • Attack Vector: Attacker provides a specially crafted spreadsheet file that causes PHPSpreadsheet to consume excessive server resources (CPU, memory) during parsing, leading to application slowdown or crash.
    • Vulnerability Focus: Inefficient handling of specific file structures or content by PHPSpreadsheet. This could be due to:
      • 1.2.1. Identify Resource Intensive Parsing Behavior:
        • Processing extremely large files or worksheets.
        • Handling files with a very high number of complex formulas.
        • Decompressing maliciously crafted compressed files (zip bombs for XLSX).
    • Exploitation Steps:
      1. Identify Resource Intensive Behavior: Determine file characteristics that cause PHPSpreadsheet to consume excessive resources.
      2. Craft Resource Exhausting File: Create a spreadsheet file with these characteristics, such as:
        • Files with millions of rows and columns.
        • Files with deeply nested and computationally expensive formulas.
        • Zip bombs that expand to enormous sizes upon decompression.
      3. Upload/Provide Resource Exhausting File: Get the application to process the crafted file, causing resource exhaustion and DoS.
    • Impact: Application becomes unavailable or severely degraded, disrupting service for legitimate users.

  • 1.3. Information Disclosure via File Parsing Errors/Exceptions:

    • 1.3.2. Application Exposes Error Messages to Attacker [CRITICAL NODE - Error Exposure]:
      • Attack Vector: Attacker provides malformed or unexpected spreadsheet files to trigger errors in PHPSpreadsheet. If the application is not properly configured, these errors, which may contain sensitive information, are displayed to the attacker.
      • Vulnerability Focus:
        • 1.3.2.1. Lack of Proper Error Handling in Application Code [CRITICAL NODE - Application Error Handling Flaw]: Application code fails to catch and handle exceptions thrown by PHPSpreadsheet gracefully, instead displaying raw error messages.
        • 1.3.2.2. Debug Mode Enabled in Production [CRITICAL NODE - Debug Mode in Prod]: Production environment is mistakenly configured with debug mode enabled, leading to verbose error output being displayed.
      • Exploitation Steps:
        1. Trigger Errors: Provide intentionally malformed or unexpected spreadsheet files to the application.
        2. Observe Error Messages: Analyze the application's response to see if detailed error messages are exposed.
      • Impact: Disclosure of sensitive information such as:
        • Internal file paths and directory structures.
        • Configuration details.
        • Potentially database connection strings or other credentials if errors originate from database interactions.

Attack Tree Path: 2. Exploit File Generation Vulnerabilities

  • 2.1. Content Injection in Generated Files [CRITICAL NODE - Content Injection]:

    • Attack Vector: Attacker injects malicious content into data that is used to generate spreadsheet files via PHPSpreadsheet. If the application doesn't properly sanitize user input, this malicious content can be embedded in the generated file.
    • Vulnerability Focus:
      • 2.1.1. Application Logic Flaws in Data Handling [CRITICAL NODE - Input Sanitization Flaw]: Application fails to sanitize user-provided data before using it to populate spreadsheet cells.
    • Exploitation Steps:
      1. Identify Injection Point: Find application features where user input is used to generate spreadsheet content.
      2. Inject Malicious Content: Provide input containing malicious payloads, such as:
        • HTML or JavaScript code if the generated file is intended to be viewed in a web browser.
        • Phishing links or deceptive text.
      3. Generate and Distribute File: Trigger the application to generate the spreadsheet file with the injected content.
      4. Gain Advantage: Distribute the malicious spreadsheet to victims, potentially for phishing attacks, defacement (if displayed online), or other social engineering attacks.
    • Impact: Phishing attacks, defacement, reputation damage, and potential compromise of users who interact with the malicious file.

  • 2.2. Formula Injection in Generated Files [CRITICAL NODE - Formula Injection]:

    • Attack Vector: Similar to content injection, but specifically targets formulas. Attacker injects malicious formulas into data used for spreadsheet generation.
    • Vulnerability Focus:
      • 2.2.1. Application Logic Flaws in Formula Generation [CRITICAL NODE - Formula Sanitization Flaw]: Application fails to sanitize user input that is used to construct formulas in generated spreadsheets.
    • Exploitation Steps:
      1. Identify Formula Injection Point: Find application features where user input is used to create spreadsheet formulas.
      2. Inject Malicious Formula: Provide input containing malicious formulas, such as:
        • Formulas that attempt to access external data sources (if enabled and not properly restricted).
        • Formulas designed to perform unexpected calculations or display misleading information.
      3. Generate and Distribute File: Trigger the application to generate the spreadsheet file with the injected formula.
      4. Recipient Executes Malicious Formula: If the generated file is shared and opened by another user, the malicious formula is executed when the spreadsheet is opened or recalculated.
    • Impact: Data manipulation within the spreadsheet, potential for recipient-side attacks if malicious formulas can interact with the recipient's system (though PHPSpreadsheet itself primarily focuses on server-side generation).

Attack Tree Path: 3. Dependency Vulnerabilities

  • 3.1. PHPSpreadsheet Relies on Vulnerable Dependencies [CRITICAL NODE - Dependency Vulnerability]:
    • Attack Vector: PHPSpreadsheet relies on third-party libraries for various functionalities. If any of these dependencies have known vulnerabilities, they can be indirectly exploited through PHPSpreadsheet.
    • Vulnerability Focus: Vulnerabilities in libraries used by PHPSpreadsheet, such as XML parsers, zip libraries, or other components.
    • Exploitation Steps:
      1. Identify Vulnerable Dependencies: Determine the dependencies used by the specific version of PHPSpreadsheet in use.
      2. Discover Known Vulnerabilities: Check vulnerability databases for known vulnerabilities in these dependencies.
      3. Exploit Dependency Vulnerability: Craft an attack that leverages PHPSpreadsheet functionality to trigger the vulnerable code path within the dependency. This might involve:
        • Providing specific file types or content that causes PHPSpreadsheet to use the vulnerable dependency in a vulnerable way.
    • Impact: Impact depends on the nature of the dependency vulnerability. It could range from DoS to RCE, depending on the exploited flaw.

Attack Tree Path: 4. Configuration/Usage Vulnerabilities

  • 4.1. Unsafe Temporary File Handling [CRITICAL NODE - Insecure Temp File Handling]:

    • Attack Vector: PHPSpreadsheet might create temporary files during file processing. If the application or server environment is misconfigured, these temporary files might be handled insecurely, leading to vulnerabilities.
    • Vulnerability Focus:
      • 4.1.2. Application Fails to Securely Manage Temporary Files [CRITICAL NODE - Application Temp File Management Flaw]:
        • Insecure Permissions on Temporary File Directory: Temporary file directories have overly permissive permissions, allowing unauthorized access.
        • Predictable Temporary File Names: Temporary file names are predictable, allowing attackers to guess and potentially access or overwrite them.
    • Exploitation Steps:
      1. Identify Temporary File Usage: Determine if and how PHPSpreadsheet uses temporary files in the application context.
      2. Exploit Insecure Handling: If temporary file handling is insecure (e.g., predictable names, weak permissions), attackers might:
        • Access temporary files to read sensitive data.
        • Overwrite temporary files to inject malicious content or disrupt processing.
    • Impact: Information disclosure, local file inclusion, potential for further exploitation depending on the content and usage of temporary files.

  • 4.2. Insecure Deserialization [CRITICAL NODE - Insecure Deserialization]:

    • Attack Vector: If the application extends PHPSpreadsheet or uses it in conjunction with serialization mechanisms, and if deserialization is performed on untrusted data without proper safeguards, insecure deserialization vulnerabilities can arise.
    • Vulnerability Focus:
      • 4.2.2. Deserialization Process is Vulnerable [CRITICAL NODE - Vulnerable Deserialization Process]: Application uses unserialize() in PHP on untrusted data that might contain serialized PHPSpreadsheet objects or related data structures.
    • Exploitation Steps:
      1. Identify Deserialization Point: Find application code where unserialize() is used on data that could be influenced by an attacker.
      2. Craft Malicious Serialized Payload: Create a malicious serialized payload that, when deserialized, executes arbitrary code on the server.
      3. Provide Malicious Payload: Inject the malicious serialized payload into the application's deserialization process (e.g., through cookies, POST parameters, or file uploads if applicable).
    • Impact: Remote Code Execution, allowing the attacker to gain complete control of the server.