- Implement proper input validation and sanitization to prevent user-supplied input from containing directory traversal sequences.
- Use whitelisting or allowlisting approaches to validate and restrict input for file paths.
- Ensure that the extracted file paths are constructed based on trusted and validated information rather than relying solely on user-provided data.
- Restrict the extraction process to a specific directory or set of allowed directories.

=== "Dart"
	```dart
	import 'dart:io';
	import 'archive/archive.dart';
	
	void extractZipFile(String path) {
	  File file = File(path);
	  Archive archive = ZipDecoder().decodeBytes(file.readAsBytesSync());
	
	  for (ArchiveFile archiveFile in archive) {
	    String extractedFilePath = '/tmp/' + sanitizeFilePath(archiveFile.name);
	
	    // Check if the extracted file path is within the allowed directory
	    if (isPathWithinAllowedDirectory(extractedFilePath)) {
	      File extractedFile = File(extractedFilePath);
	      extractedFile.createSync(recursive: true);
	      extractedFile.writeAsBytesSync(archiveFile.content);
	    }
	  }
	}
	
	String sanitizeFilePath(String filePath) {
	  // Implement logic to sanitize the file path and remove any potentially harmful characters or sequences
	  // Return the sanitized file path
	}
	
	bool isPathWithinAllowedDirectory(String filePath) {
	  // Implement logic to check if the extracted file path is within the allowed directory
	  // Return true if the file path is allowed, false otherwise
	}
	```


=== "Swift"
	```Swift
	import Foundation
	
	func extractZipFile(path: String) {
	    guard let archive = Archive(url: URL(fileURLWithPath: path), accessMode: .read) else {
	        return
	    }
	
	    let destinationDir = URL(fileURLWithPath: "/tmp/")
	
	    for entry in archive {
	        let extractedFilePath = sanitizeFilePath(entry.path)
	
	        // Check if the extracted file path is within the allowed directory
	        if isPathWithinAllowedDirectory(extractedFilePath) {
	            let extractedFileURL = destinationDir.appendingPathComponent(extractedFilePath)
	
	            do {
	                try archive.extract(entry, to: extractedFileURL)
	            } catch {
	                print("Error extracting file: \(error)")
	            }
	        }
	    }
	}
	
	func sanitizeFilePath(_ filePath: String) -> String {
	    // Implement logic to sanitize the file path and remove any potentially harmful characters or sequences
	    // Return the sanitized file path
	}
	
	func isPathWithinAllowedDirectory(_ filePath: String) -> Bool {
	    // Implement logic to check if the extracted file path is within the allowed directory
	    // Return true if the file path is allowed, false otherwise
	}
	```


=== "Kotlin"
	```kotlin
	import java.io.File
	import java.util.zip.ZipEntry
	import java.util.zip.ZipFile
	
	fun extractZipFile(path: String) {
	    val file = File(path)
	    val zipFile = ZipFile(file)
	
	    val destinationDir = File("/tmp/")
	    val zipEntries = zipFile.entries()
	
	    while (zipEntries.hasMoreElements()) {
	        val zipEntry = zipEntries.nextElement()
	        val extractedFilePath = sanitizeFilePath(zipEntry.name)
	
	        // Check if the extracted file path is within the allowed directory
	        if (isPathWithinAllowedDirectory(extractedFilePath)) {
	            val extractedFile = File(destinationDir, extractedFilePath)
	            extractedFile.parentFile.mkdirs()
	            extractedFile.outputStream().use { outputStream ->
	                zipFile.getInputStream(zipEntry).copyTo(outputStream)
	            }
	        }
	    }
	    zipFile.close()
	}
	
	fun sanitizeFilePath(filePath: String): String {
	    // Implement logic to sanitize the file path and remove any potentially harmful characters or sequences
	    // Return the sanitized file path
	}
	
	fun isPathWithinAllowedDirectory(filePath: String): Boolean {
	    // Implement logic to check if the extracted file path is within the allowed directory
	    // Return true if the file path is allowed, false otherwise
	}
	```



### Zip Symbolic Link
- Before extracting files, check for symbolic links within the ZIP archive and ensure they are not followed blindly during extraction.
- Validate and sanitize the symbolic link target to prevent directory traversal or access to sensitive system files.
- Use platform-specific functions or libraries that handle symbolic links securely and prevent the creation of malicious links.
- Limit the extraction process to known-safe locations and avoid allowing symbolic links to be created outside of those boundaries.
- Ignore symlinks


=== "Dart"
	```dart
	import 'dart:io';
	import 'archive/archive.dart';
	import 'path';
	
	void extractZipFile(String path) {
	  File file = File(path);
	  Archive archive = ZipDecoder().decodeBytes(file.readAsBytesSync());
	
	  for (ArchiveFile archiveFile in archive) {
	    if (!isSymbolicLink(archiveFile)) {
	      // Extract regular file
	      String extractedFilePath = '/tmp/' + sanitizePath(archiveFile.name);
	      File extractedFile = File(extractedFilePath);
	      extractedFile.createSync(recursive: true);
	      extractedFile.writeAsBytesSync(archiveFile.content);
	    } 
	  }
	}
	
	bool isSymbolicLink(ArchiveFile archiveFile) {
	  // Implement platform-specific logic to check if the file is a symbolic link
	  // Return true if it is a symbolic link, false otherwise
	} 
	```


=== "Swift"
	```Swift
	import Foundation
	import ZIPFoundation
	
	func extractZipFile(path: String) {
	    let fileManager = FileManager.default
	    guard let archive = Archive(url: URL(fileURLWithPath: path), accessMode: .read) else {
	        return
	    }
	
	    for entry in archive {
	        if !isSymbolicLink(entry) {
	            // Extract regular file
	            let extractedFilePath = "/tmp/" + sanitizePath(entry.path)
	            let extractedFileURL = URL(fileURLWithPath: extractedFilePath)
	            fileManager.createFile(atPath: extractedFilePath, contents: entry.data, attributes: nil)
	        } 
	    }
	}
	
	func isSymbolicLink(_ entry: Entry) -> Bool {
	    // Implement platform-specific logic to check if the entry is a symbolic link
	    // Return true if it is a symbolic link, false otherwise
	}
	```


=== "Kotlin"
	```Kotlin
	import java.io.File
	import java.nio.file.FileSystems
	import java.nio.file.Files
	import java.nio.file.Path
	import java.nio.file.StandardCopyOption
	import java.nio.file.attribute.PosixFilePermission
	import java.util.zip.ZipInputStream
	
	fun extractZipFile(path: String) {
	    val file = File(path)
	    val zipInput = ZipInputStream(file.inputStream())
	    var entry = zipInput.nextEntry
	    while (entry != null) {
	        if (!isSymbolicLink(entry)) {
	            // Extract regular file
	            val extractedFilePath = File("/tmp", sanitizePath(entry.name))
	            extractedFilePath.parentFile.mkdirs()
	            Files.copy(zipInput, extractedFilePath.toPath(), StandardCopyOption.REPLACE_EXISTING)
	        } 
	        entry = zipInput.nextEntry
	    }
	}
	
	fun isSymbolicLink(entry: ZipEntry): Boolean {
	    // Implement platform-specific logic to check if the entry is a symbolic link
	    // Return true if it is a symbolic link, false otherwise
	}
	```



### Zip Extension Spoofing
- Perform additional checks or validations on the extracted files to ensure that their true file type matches the expected extension.
- Consider using file signatures or magic numbers to verify the file's content and compare it with the indicated extension.
- Implement file type verification based on both the extension and the file header to ensure consistency.
- Consider using third-party libraries or tools specifically designed to handle ZIP files securely, as they may provide built-in protection against extension spoofing attacks.


=== "Dart"
	```Dart
	import 'dart:io';
	import 'archive/archive.dart';
	import 'path';
	
	void extractZipFile(String path) {
	  File file = File(path);
	  Archive archive = ZipDecoder().decodeBytes(file.readAsBytesSync());
	
	  for (ArchiveFile archiveFile in archive) {
	    // Mitigation: Validate the file type by comparing the extension and file header
	    if (isFileExtensionValid(archiveFile) && isFileHeaderValid(archiveFile)) {
	      String extractedFilePath = '/tmp/' + sanitizePath(archiveFile.name);
	      File extractedFile = File(extractedFilePath);
	      extractedFile.createSync(recursive: true);
	      extractedFile.writeAsBytesSync(archiveFile.content);
	    } else {
	      // Handle case when file type does not match the expected extension
	      print('Invalid file type detected: ${archiveFile.name}');
	    }
	  }
	}
	
	bool isFileExtensionValid(ArchiveFile archiveFile) {
	  // Implement logic to validate the file extension against expected extensions
	  // Return true if the file extension is valid, false otherwise
	}
	
	bool isFileHeaderValid(ArchiveFile archiveFile) {
	  // Implement logic to validate the file header and ensure it matches the expected file type
	  // Return true if the file header is valid, false otherwise
	}
	```


=== "Swift"
	```Swift
	import Foundation
	import ZIPFoundation
	
	func extractZipFile(path: String) {
	    let fileManager = FileManager.default
	    guard let archive = Archive(url: URL(fileURLWithPath: path), accessMode: .read) else {
	        return
	    }
	
	    for entry in archive {
	        // Mitigation: Validate the file type by comparing the extension and file header
	        if isFileExtensionValid(entry) && isFileHeaderValid(entry) {
	            let extractedFilePath = "/tmp/" + sanitizePath(entry.path)
	            let extractedFileURL = URL(fileURLWithPath: extractedFilePath)
	            fileManager.createFile(atPath: extractedFilePath, contents: entry.data, attributes: nil)
	        } else {
	            // Handle case when file type does not match the expected extension
	            print("Invalid file type detected: \(entry.path)")
	        }
	    }
	}
	
	func isFileExtensionValid(_ entry: Entry) -> Bool {
	    // Implement logic to validate the file extension against expected extensions
	    // Return true if the file extension is valid, false otherwise
	}
	
	func isFileHeaderValid(_ entry: Entry) -> Bool {
	    // Implement logic to validate the file header and ensure it matches the expected file type
	    // Return true if the file header is valid, false otherwise
	}
	```


=== "Kotlin"
	```kotlin
	import java.io.File
	import java.nio.file.FileSystems
	import java.nio.file.Files
	import java.nio.file.Path
	import java.nio.file.StandardCopyOption
	import java.nio.file.attribute.PosixFilePermission
	import java.util.zip.ZipInputStream
	
	fun extractZipFile(path: String) {
	    val file = File(path)
	    val zipInput = ZipInputStream(file.inputStream())
	    var entry = zipInput.nextEntry
	    while (entry != null) {
	        // Mitigation: Validate the file type by comparing the extension and file header
	        if (isFileExtensionValid(entry) && isFileHeaderValid(entry)) {
	            val extractedFilePath = File("/tmp", sanitizePath(entry.name))
	            extractedFilePath.parentFile.mkdirs()
	            Files.copy(zipInput, extractedFilePath.toPath(), StandardCopyOption.REPLACE_EXISTING)
	        } else {
	            // Handle case when file type does not match the expected extension
	            println("Invalid file type detected: ${entry.name}")
	        }
	        entry = zipInput.nextEntry
	    }
	}
	
	fun isFileExtensionValid(entry: ZipEntry): Boolean {
	    // Implement logic to validate the file extension against expected extensions
	    // Return true if the file extension is valid, false otherwise
	}
	
	fun isFileHeaderValid(entry: ZipEntry): Boolean {
	    // Implement logic to validate the file header and ensure it matches the expected file type
	    // Return true if the file header is valid, false otherwise
	}
	```
