All file-related operations must implement comprehensive input validation and sanitization to prevent path traversal attacks, arbitrary file system access, and execution of malicious content. This is especially critical when handling user-provided file paths or when systems interact with AI agents that could be manipulated through prompt injection. Key validation requirements: - **Filename sanitization**: Strip all non-alphanumeric characters except spaces, underscores, and hyphens. Replace invalid characters with underscores. Limit filenames to 64 characters maximum. - **Extension restrictions**: Only allow specific safe file extensions (e.g., `.txt`, `.pdf`) based on the use case. - **Path traversal prevention**: Reject any paths containing `..`, `/`, or `\` characters. Validate that paths don't resolve to dangerous system directories. - **Directory restrictions**: Explicitly block access to sensitive directories like `/`, `~`, `~/Desktop`, `~/Documents`. Restrict operations to dedicated safe directories or current working directory. - **Executable prevention**: Check for script indicators like `#!` at file start and verify no executable permission bits are set after file creation. Example implementation: ```python def validate_file_path(file_path: str, allowed_extensions: list[str]) -> str: # Check for dangerous directories dangerous_paths = ['/', '~', '~/Desktop', '~/Documents'] if file_path in dangerous_paths: raise ValueError(f"Access to {file_path} is not allowed") # Extract filename and validate filename = Path(file_path).name # Sanitize filename sanitized = re.sub(r'[^a-zA-Z0-9 _-]', '_', filename) if len(sanitized) > 64: sanitized = sanitized[:64] # Check extension if not any(sanitized.endswith(ext) for ext in allowed_extensions): raise ValueError(f"File extension not allowed: {sanitized}") return sanitized ``` This prevents AI agents or malicious users from writing to system files, executing scripts, or accessing sensitive directories through path traversal attacks.