HTML Injection Vulnerability

Description

HTML injection is a security vulnerability that occurs when user-manipulated input in a mobile application can be used to insert arbitrary HTML code into a vulnerable webview. This vulnerability can be exploited to launch various attacks, such as stealing a user's session tokens or CSRF tokens, which can then be used for further malicious activities. Additionally, it allows attackers to modify the content displayed to victims, giving them the ability to insert malicious code or deface the page with their own message.

DartSwiftKotlin

import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'HTML Injection Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: WebViewScreen(),
    );
  }
}

class WebViewScreen extends StatefulWidget {
  @override
  _WebViewScreenState createState() => _WebViewScreenState();
}

class _WebViewScreenState extends State<WebViewScreen> {
  late WebViewController _webViewController;
  String? htmlInput;

  @override
  void initState() {
    super.initState();
    getHtmlInputFromIntent();
  }

  void getHtmlInputFromIntent() {
    // Retrieve the intent extras
    Map<String, dynamic>? extras = ModalRoute.of(context)?.settings.arguments as Map<String, dynamic>?;

    // Extract the user input from the intent extras
    htmlInput = extras?['htmlInput'];
  }

  void _injectHtml() async {
    if (htmlInput != null) {
      await _webViewController.loadUrl(Uri.dataFromString(htmlInput!, mimeType: 'text/html').toString());
    }
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('HTML Injection Demo'),
      ),
      body: Column(
        children: [
          ElevatedButton(
            onPressed: _injectHtml,
            child: Text('Inject HTML'),
          ),
          Expanded(
            child: WebView(
              initialUrl: 'about:blank',
              onWebViewCreated: (WebViewController controller) {
                _webViewController = controller;
              },
            ),
          ),
        ],
      ),
    );
  }
}

import UIKit
import WebKit

class ViewController: UIViewController, WKNavigationDelegate {

    var webView: WKWebView!
    var htmlInput: String?

    override func viewDidLoad() {
        super.viewDidLoad()

        // Retrieve the user input from the intent extras
        if let extras = self.navigationController?.navigationBar.accessibilityUserInputLabels {
            htmlInput = extras["htmlInput"] as? String
        }

        // Create and configure the web view
        webView = WKWebView(frame: view.bounds)
        webView.navigationDelegate = self
        view.addSubview(webView)

        // Load the web page
        let htmlString = "<html><body><h1>\(htmlInput ?? "")</h1></body></html>"
        webView.loadHTMLString(htmlString, baseURL: nil)
    }
}

import android.annotation.SuppressLint
import android.os.Bundle
import android.webkit.WebSettings
import android.webkit.WebView
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {

    private lateinit var webView: WebView

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

        webView = findViewById(R.id.webView)

        val name = intent.getStringExtra("name")

        val html = "<html><body><h1>Hello, $name!</h1></body></html>"
        webView.loadDataWithBaseURL(null, html, "text/html", "UTF-8", null)

        val webSettings: WebSettings = webView.settings
        webSettings.javaScriptEnabled = false
    }
}

Recommendation

To mitigate the risks associated with HTML injection vulnerabilities, the following recommendations should be implemented:

Sanitize User Input: Perform proper input validation and sanitization on user-supplied data that will be rendered as part of HTML code. Use encoding techniques to ensure that user input is treated as data and not executable code.
Use Templating Engines: Utilize secure templating engines or frameworks that automatically escape user input by default, such as Handlebars, Twig, or Django templates. These engines help prevent HTML injection by properly handling user input.
Whitelisting Input: Implement whitelisting or allow listing approaches to validate and restrict input for HTML elements, attributes, and protocols. Only allow specific tags, attributes, and protocols that are necessary for the application's functionality.
Contextual Output Encoding: Encode user-generated content based on its context. Different contexts, such as HTML attributes, JavaScript code, or CSS styles, require specific encoding techniques to prevent HTML injection attacks. Use appropriate encoding functions or libraries based on the context.

DartSwiftKotlin

import 'package:flutter/material.dart';
import 'package:webview_flutter/webview_flutter.dart';
import 'package:sanitize_html/sanitize_html.dart' show sanitizeHtml;

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'HTML Injection Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: WebViewScreen(),
    );
  }
}

class WebViewScreen extends StatefulWidget {
  @override
  _WebViewScreenState createState() => _WebViewScreenState();
}

class _WebViewScreenState extends State<WebViewScreen> {
  late WebViewController _webViewController;
  String? htmlInput;

  @override
  void initState() {
    super.initState();
    getHtmlInputFromIntent();
  }

  void getHtmlInputFromIntent() {
    // Retrieve the intent extras
    Map<String, dynamic>? extras =
        ModalRoute.of(context)?.settings.arguments as Map<String, dynamic>?;

    // Extract the user input from the intent extras
    htmlInput = extras?['htmlInput'];
  }

  void _injectHtml() async {
    if (htmlInput != null) {
      final sanitizedHtml = sanitizeHtml(htmlInput);
      await _webViewController.loadUrl(
        Uri.dataFromString(sanitizedHtml, mimeType: 'text/html', encoding: Encoding.getByName('utf-8'))!.toString(),
      );
    }
  }


  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('HTML Injection Demo'),
      ),
      body: Column(
        children: [
          ElevatedButton(
            onPressed: _injectHtml,
            child: Text('Inject HTML'),
          ),
          Expanded(
            child: WebView(
              initialUrl: 'about:blank',
              onWebViewCreated: (WebViewController controller) {
                _webViewController = controller;
              },
            ),
          ),
        ],
      ),
    );
  }
}

import UIKit
import WebKit
import DOMPurify

class ViewController: UIViewController, WKNavigationDelegate {

    private var webView: WKWebView!

    override func viewDidLoad() {
        super.viewDidLoad()

        webView = WKWebView(frame: view.bounds)
        webView.navigationDelegate = self
        view.addSubview(webView)

        let name = "John Doe"
        let plainText = "Hello, \(name)!"
        let sanitizedText = sanitizeHTML(plainText)
        let html = "<html><body><h1>\(sanitizedText)</h1></body></html>"
        webView.loadHTMLString(html, baseURL: nil)
    }

    private func sanitizeHTML(_ html: String) -> String {
        guard let sanitized = DOMPurify.sanitize(html) else {
            return ""
        }
        return sanitized
    }
}

import android.annotation.SuppressLint
import android.os.Bundle
import android.webkit.WebSettings
import android.webkit.WebView
import androidx.appcompat.app.AppCompatActivity

class MainActivity : AppCompatActivity() {

    private lateinit var webView: WebView

    PolicyFactory policy = new HtmlPolicyBuilder()
        .allowElements("a")
        .allowUrlProtocols("https")
        .allowAttributes("href").onElements("a")
        .requireRelNofollowOnLinks()
        .build();

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

        webView = findViewById(R.id.webView)

        val name = intent.getStringExtra("name")
        val sanitizedName = policy.sanitize(name)   

        val html = "<html><body><h1>Hello, $sanitizedName!</h1></body></html>"
        webView.loadDataWithBaseURL(null, html, "text/html", "UTF-8", null)

        val webSettings: WebSettings = webView.settings
        webSettings.javaScriptEnabled = false
    }

}

Links

Standards

OWASP_TOP_10:
- A3:2017-Sensitive Data Exposure
- A7:2017-Cross-Site Scripting (XSS)
OWASP_MASVS_L1:
- MSTG_PLATFORM_5
- MSTG_PLATFORM_7
OWASP_MASVS_L2:
- MSTG_PLATFORM_5
- MSTG_PLATFORM_7
PCI_STANDARDS:
- REQ_6_2
- REQ_6_3
- REQ_6_4
- REQ_11_3