When an attacker gains control over the URL used by an application to fetch content, it introduces a critical security risk. By manipulating the URL, the attacker can redirect the application to a malicious server or inject their own content into the response. This can lead to various security vulnerabilities and potential consequences. For instance:

* Code Execution: The attacker may alter the URL to point to a server they control, enabling them to deliver malicious code to the application. This code could exploit vulnerabilities in the application, execute arbitrary commands, or install malware on the user's system.
* Data Theft: By redirecting the application to a fraudulent server, the attacker can trick users into entering sensitive information such as login credentials, credit card details, or personal data, which can then be captured and misused.
* Content Manipulation: The attacker can modify the content retrieved by the application, altering the displayed information or injecting malicious scripts. This can lead to various consequences such as displaying misleading information, defacing webpages, or conducting phishing attacks.
* Supply Chain Attacks: If the application fetches content from external sources, such as libraries or plugins, controlling the URL can allow the attacker to replace legitimate resources with compromised or malicious versions. This can compromise the security of the entire system.

Below is a sample code of an application fetching attacker controlled input:

`Kotlin`

```kotlin
import android.content.Intent
import android.net.Uri
import android.os.Bundle
import androidx.appcompat.app.AppCompatActivity
import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.GlobalScope
import kotlinx.coroutines.launch
import java.io.BufferedReader
import java.io.InputStreamReader
import java.net.HttpURLConnection
import java.net.URL

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        // Get the URL from the intent
        val intent: Intent = intent
        val url: String? = intent.getStringExtra("url")

        if (url != null) {
            // Fetch the content from the provided URL
            GlobalScope.launch(Dispatchers.IO) {
                val content: String? = fetchContent(url)
                // Process the fetched content as needed
                if (content != null) {
                    // TODO: Process the fetched content here
                }
            }
        }
    }

    private fun fetchContent(urlString: String): String? {
        var connection: HttpURLConnection? = null
        var reader: BufferedReader? = null

        try {
            val url = URL(urlString)
            connection = url.openConnection() as HttpURLConnection
            connection.requestMethod = "GET"

            // Check if the response code is successful
            if (connection.responseCode == HttpURLConnection.HTTP_OK) {
                reader = BufferedReader(InputStreamReader(connection.inputStream))
                val response = StringBuilder()
                var line: String?

                // Read the response line by line
                while (reader.readLine().also { line = it } != null) {
                    response.append(line)
                }

                return response.toString()
            }
        } catch (e: Exception) {
            e.printStackTrace()
        } finally {
            // Close the connection and reader
            connection?.disconnect()
            reader?.close()
        }

        return null
    }
}
```

`Dart`

```dart
import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;

class MainActivity extends StatefulWidget {
  final String url;

  MainActivity({required this.url});

  @override
  _MainActivityState createState() => _MainActivityState();
}

class _MainActivityState extends State<MainActivity> {
  String? content;

  @override
  void initState() {
    super.initState();
    fetchContent(widget.url);
  }

  Future<void> fetchContent(String url) async {
    try {
      final response = await http.get(Uri.parse(url));

      if (response.statusCode == 200) {
        setState(() {
          content = response.body;
        });
        // TODO: Process the fetched content here
      } else {
        // Handle error response
      }
    } catch (e) {
      // Handle network or API call error
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Fetching URL Content'),
      ),
      body: Center(
        child: content != null
            ? Text(content!)
            : CircularProgressIndicator(),
      ),
    );
  }
}
```

`Swift`

```swift
import UIKit

class AppDelegate: UIResponder, UIApplicationDelegate {

    var window: UIWindow?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Handle deep link URL if the app was launched from a URL
        if let url = launchOptions?[.url] as? URL {
            handleDeepLink(url)
        }
        return true
    }

    func application(_ application: UIApplication, open url: URL, options: [UIApplication.OpenURLOptionsKey : Any] = [:]) -> Bool {
        // Handle deep link URL when the app is already running
        handleDeepLink(url)
        return true
    }

    private func handleDeepLink(_ url: URL) {
        // Check if the URL scheme is "ostorlab"
        if url.scheme == "ostorlab" {
            // Extract the URL from the deep link
            if let deepLinkURL = URL(string: url.absoluteString.replacingOccurrences(of: "ostorlab://", with: "")) {
                // Fetch the content from the provided URL
                fetchContent(deepLinkURL)
            }
        }
    }

    private func fetchContent(_ url: URL) {
        URLSession.shared.dataTask(with: url) { (data, response, error) in
            if let error = error {
                print("Error fetching content: \(error.localizedDescription)")
                return
            }
            if let data = data, let content = String(data: data, encoding: .utf8) {
                // Process the fetched content here
                print("Fetched content: \(content)")
            }
        }.resume()
    }
}
```