To mitigate Regular Expression Denial of Service (ReDoS) vulnerabilities consider the following recommendations:


* **Minimize Dependency on User Input:**
Whenever feasible, minimize the reliance on user-supplied input for constructing regular expressions (regex). Consider alternative approaches or design patterns that reduce the need for dynamic regex generation based on user input. By limiting exposure to potentially malicious patterns, you can significantly decrease the risk of ReDoS vulnerabilities.


* **Validate User Input:**
Implement robust validation mechanisms to ensure that user-provided input for regex construction adheres to predefined criteria. Validate the length, complexity, and structure of input patterns to mitigate the risk of maliciously crafted expressions. By validating input at the outset, you can preemptively identify and reject potentially harmful patterns.

  
* **Implement Rate Limiting and Timeout Mechanisms:**
Apply rate limiting and timeout mechanisms to restrict the execution time and resource consumption associated with regex evaluation. Set appropriate limits on the complexity and duration of regex matching operations to prevent excessive computational overhead. By imposing reasonable constraints on regex processing, you can mitigate the risk of ReDoS attacks and ensure the stability of your application under varying input conditions.

=== "Java"
  ```java
 import java.util.Scanner;
 import java.util.concurrent.*;
 
 public class TimeoutDatabaseCheckExample {
     public static void main(String[] args) {
         // Create a Scanner object to read user input
         Scanner scanner = new Scanner(System.in);
 
         // Prompt the user to enter a regex pattern
         System.out.print("Enter a regex pattern: ");
         String regexPattern = scanner.nextLine();
 
         // Set the timeout duration in milliseconds
         long timeoutDuration = 1000; // 1 second
 
         // Create an ExecutorService with a single thread
         ExecutorService executor = Executors.newSingleThreadExecutor();
 
         // Submit the database check task to the executor
         Future<Boolean> future = executor.submit(() -> {
             // Perform the database check operation
             return checkDatabase(regexPattern);
         });
 
         try {
             // Wait for the result with timeout
             boolean recordExists = future.get(timeoutDuration, TimeUnit.MILLISECONDS);
 
             // Check if the record exists in the database
             if (recordExists) {
                 System.out.println("Record exists in the database!");
             } else {
                 System.out.println("Record not found in the database.");
             }
         } catch (TimeoutException e) {
             // Handle timeout
             System.out.println("Database operation timed out.");
         } catch (InterruptedException | ExecutionException e) {
             // Handle other exceptions
             e.printStackTrace();
         } finally {
             // Shutdown the executor
             executor.shutdown();
         }
 
         // Close the scanner
         scanner.close();
     }
 
     // Hypothetical database check function
     public static boolean checkDatabase(String regexPattern) {
         // Perform the database check operation here
         // For demonstration purposes, assume the record exists if the regex pattern matches
         return Pattern.compile(regexPattern).matcher("record_from_database").find();
     }
 }
 
 ```
=== "Swift"
  ```swift
 import Foundation
 
 // Function to perform database check
 func checkDatabase(forRegexPattern regexPattern: String) -> Bool {
     // Perform the database check operation here
     // For demonstration purposes, assume the record exists if the regex pattern matches
     let inputString = "record_from_database"
     return inputString.range(of: regexPattern, options: .regularExpression) != nil
 }
 
 // Function to perform database check with timeout
 func checkDatabaseWithTimeout(forRegexPattern regexPattern: String, timeout: TimeInterval) -> Bool? {
     var result: Bool?
     
     // Create a dispatch group
     let group = DispatchGroup()
     
     // Create a dispatch queue
     let queue = DispatchQueue.global()
     
     // Enter the dispatch group
     group.enter()
     
     // Asynchronously perform the database check operation
     queue.async {
         result = checkDatabase(forRegexPattern: regexPattern)
         // Leave the dispatch group when the operation is complete
         group.leave()
     }
     
     // Wait for the operation to complete with timeout
     let dispatchResult = group.wait(timeout: .now() + timeout)
     
     // Check if the operation timed out
     if dispatchResult == .timedOut {
         // Return nil indicating timeout
         return nil
     }
     
     // Return the result of the database check operation
     return result
 }
 
 // Function to get regex pattern from user input
 func getRegexPatternFromUser() -> String {
     print("Enter the regex pattern:")
     guard let input = readLine() else {
         return ""
     }
     return input
 }
 
 // Example usage
 let regexPattern = getRegexPatternFromUser()
 let timeoutDuration = 1.0 // Timeout duration in seconds
 
 if !regexPattern.isEmpty {
     if let recordExists = checkDatabaseWithTimeout(forRegexPattern: regexPattern, timeout: timeoutDuration) {
         if recordExists {
             print("Record exists in the database!")
         } else {
             print("Record not found in the database.")
         }
     } else {
         print("Database operation timed out.")
     }
 } else {
     print("Invalid regex pattern.")
 }
 
  ```