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Attack Tree Analysis for spartnernl/laravel-excel

Objective: Exfiltrate sensitive data, execute arbitrary code, or disrupt service availability by exploiting vulnerabilities within the laravel-excel package or its dependencies.

Attack Tree Visualization

                                      Attacker's Goal:
                                Exfiltrate Data, Execute Code, or Disrupt Service
                                              |
                      -----------------------------------------------------------------
                      |                               |                               
        1.  Data Exfiltration                  2.  Code Execution                
                      |                               |                               
        -------------------------         ---------------------------------        
        |                       |         |                 |                 |        
        -                       **1.2 Formula**     **2.1  CSV Injection**  **2.2  XXE via**
                                **Injection (DDE)**         **(DDE)**             LibreOffice/
                                                                                  OpenOffice
                                                                                  (if used)
        |                       |         |                 |                        
        -                       **1.2.1**   1.2.2   **2.1.1  Injecting**   **2.2.1  Crafting**
                                **Execute**  Execute  **malicious**       **malicious**
                                **OS**       Excel    **formulas to**     **XML to**
                                **Commands**  Macros   **read files,**     **trigger XXE**
                                                     **perform SSRF,**
                                                     **or execute**
                                                     **code.**

Attack Tree Path: 1.2 Formula Injection (DDE)

  • Description: This attack vector exploits the Dynamic Data Exchange (DDE) feature in Excel (and potentially other spreadsheet applications). Attackers can craft malicious formulas that, when opened in a vulnerable application, execute arbitrary commands on the user's operating system. This is a client-side vulnerability triggered by a server-side flaw (lack of input sanitization).

    • Sub-Steps:

      • 1.2.1 Execute OS Commands (Critical Node):
        • Description: The attacker inserts a formula like =CMD|' /C calc'!A0 (or more sophisticated variations) into a cell. When the file is opened, and DDE is enabled (or can be tricked into enabling), the operating system command (calc in this example, but it could be anything) is executed.
        • Likelihood: High (if user input is not sanitized).
        • Impact: High (complete system compromise, data theft, malware installation).
        • Effort: Low (simple formulas can be used).
        • Skill Level: Medium (understanding of Excel formulas and DDE).
        • Detection Difficulty: Medium to High (can be obfuscated, requires careful file analysis).
      • 1.2.2 Execute Excel Macros:
        • Description: Similar to command execution, but involves injecting malicious VBA macros. Requires the user to enable macros.
        • Likelihood: Medium (depends on user enabling macros).
        • Impact: High (similar to OS command execution, but potentially more persistent).
        • Effort: Medium (requires knowledge of VBA).
        • Skill Level: Medium to High.
        • Detection Difficulty: Medium (macro analysis can be complex).

    • Actionable Insights (for the entire 1.2 path):

      • CRITICAL: Implement robust formula sanitization. This is the primary defense. Escape or remove dangerous characters (e.g., =, +, -, @, |, !) at the beginning of cell values. Prepending a single quote (') is a simple and effective method. Use regular expressions to detect and neutralize more complex formula patterns.
      • Disable DDE if possible: If DDE is not required, disable it at the operating system or application level.
      • User Education: Train users to be wary of opening Excel files from untrusted sources and to avoid enabling macros unless absolutely necessary.

Attack Tree Path: 2.1 CSV Injection (DDE)

  • Description: This is a variant of formula injection that targets CSV files. If the application allows users to upload CSV files that are later processed by laravel-excel (or any library that handles CSV), the attacker can inject malicious formulas into the CSV data.

    • Sub-Steps:

      • 2.1.1 Injecting malicious formulas (Critical Node):
        • Description: Identical in principle to 1.2.1, but the injection point is a CSV file instead of a directly generated Excel file. The formulas are designed to be executed when the CSV is opened in Excel or imported into another application.
        • Likelihood: High (if user-supplied CSV files are processed without sanitization).
        • Impact: High (same as 1.2.1).
        • Effort: Low.
        • Skill Level: Medium.
        • Detection Difficulty: Medium to High.

    • Actionable Insights (for the entire 2.1 path):

      • CRITICAL: Apply the same rigorous formula sanitization techniques used for Excel data to any CSV data that is processed. Treat CSV input as untrusted.
      • Validate CSV Structure: Ensure the CSV file conforms to expected structure and data types.

Attack Tree Path: 2.2 XXE via LibreOffice/OpenOffice (if used)

  • Description: This attack targets the XML processing capabilities of LibreOffice or OpenOffice, if they are used by the server for file conversion or other tasks. XXE (XML External Entity) vulnerabilities allow attackers to include external entities in XML documents, which can be exploited to read local files, access internal network resources, or even execute code.

    • Sub-Steps:

      • 2.2.1 Crafting malicious XML to trigger XXE (Critical Node):
        • Description: The attacker crafts a malicious Excel file (which is internally an XML-based format) that includes an XXE payload. This payload might try to read sensitive files (e.g., /etc/passwd), access internal network services (SSRF), or even attempt remote code execution (RCE) depending on the specific vulnerabilities present.
        • Likelihood: Medium (depends on whether LibreOffice/OpenOffice is used and its configuration).
        • Impact: High (potential for file disclosure, SSRF, RCE).
        • Effort: Medium (requires knowledge of XXE vulnerabilities and XML).
        • Skill Level: Medium to High.
        • Detection Difficulty: High (requires careful XML parsing and analysis).

    • Actionable Insights (for the entire 2.2 path):

      • CRITICAL: If LibreOffice/OpenOffice is used, ensure that XML external entity processing is DISABLED. This is the most important mitigation.
      • Input Validation: Validate any XML input, even if it's indirectly generated from user-supplied data.
      • Least Privilege: Run LibreOffice/OpenOffice with the minimum necessary privileges.
      • Network Segmentation: If possible, isolate the server that handles file conversions to limit the impact of a successful XXE attack.