Learn how to protect your data and your users from security risks when using HTML5 local storage. Follow these best practices and tips to prevent XSS attacks, encrypt the data, and limit the scope and duration of the data.

HTML5 local storage is a feature that allows web applications to store data locally on the user's browser. It provides a way to store key-value pairs of data, similar to cookies, but with a larger storage capacity and improved performance. The data stored in local storage is persistent and remains available even after the browser is closed or the computer is restarted. It can be accessed and manipulated using JavaScript, making it a powerful tool for web developers to create interactive and personalized experiences for users.

To limit the scope and duration of HTML5 local storage data: Use sessionStorage for session-specific data that should be deleted when the browser is closed. Utilize origin-specific storage to restrict access to data from specific subdomains or protocols. Set expiration dates or time-to-live values for the data and delete it when it becomes invalid. These measures help protect user privacy and prevent the accumulation of outdated or irrelevant data.

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How can you use HTML5 local storage safely?

HTML5 local storage is a feature that allows you to store data on the user's browser, without relying on cookies or server-side databases. It can be useful for enhancing the performance, functionality, and user experience of your web applications. However, it also comes with some security risks that you need to be aware of and mitigate. In this article, you will learn how to use HTML5 local storage safely, by following some best practices and tips.

1 What is HTML5 local storage?

HTML5 local storage is a key-value pair storage mechanism that lets you store data on the user's browser, up to 5 MB per domain. You can access and manipulate the data using JavaScript, without sending it to the server or expiring it after a session. This makes it faster and more efficient than cookies, which are limited in size and require HTTP requests. You can use HTML5 local storage for various purposes, such as caching data, saving user preferences, storing form inputs, or creating offline web applications.

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Islati Sk

Director & Founder; Software Engineer & Developer
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HTML5 local storage is a feature that allows web applications to store data locally on the user's browser. It provides a way to store key-value pairs of data, similar to cookies, but with a larger storage capacity and improved performance. The data stored in local storage is persistent and remains available even after the browser is closed or the computer is restarted. It can be accessed and manipulated using JavaScript, making it a powerful tool for web developers to create interactive and personalized experiences for users.

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2 What are the security risks of HTML5 local storage?

HTML5 local storage is not encrypted, meaning that anyone who can access the user's browser can potentially read or modify the data. This can expose sensitive information, such as personal details, passwords, tokens, or credit card numbers, to malicious actors or third-party scripts. Moreover, HTML5 local storage is vulnerable to cross-site scripting (XSS) attacks, which can inject malicious code into your web pages and access or manipulate the data. Therefore, you need to take some precautions to protect your data and your users from these threats.

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Islati Sk

Director & Founder; Software Engineer & Developer
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HTML local storage poses security risks due to lack of encryption, vulnerability to XSS attacks, potential Same Origin Policy bypass, and data leakage to scripts on the same domain. To mitigate these risks, developers should encrypt sensitive data, validate user input, implement strict content security policies, and regularly update security measures. While local storage can be useful for non-sensitive data, caution and proper security measures are necessary.

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3 How to prevent XSS attacks on HTML5 local storage?

XSS attacks are one of the most common and dangerous web security vulnerabilities, which can compromise your web application and your user's data. To protect against such attacks on HTML5 local storage, you should validate and sanitize all user inputs before storing or displaying them. Additionally, escape and encode all output from HTML5 local storage or user inputs before inserting them into the HTML document. Utilizing a library or framework, such as OWASP ESAPI or ReactJS, can assist with this process. Moreover, you can use Content Security Policy (CSP) to restrict the sources and types of scripts that can run on your web page, thus preventing malicious scripts from accessing or modifying your HTML5 local storage data. This can be accomplished by setting the CSP header on your server or in your HTML meta tag.

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Islati Sk

Director & Founder; Software Engineer & Developer
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To prevent XSS attacks on HTML5 local storage, implement input validation, output encoding, use trusted libraries/frameworks, apply Content Security Policy (CSP), regularly update software, follow secure coding practices, and conduct security testing. These measures reduce the risk of XSS attacks and enhance web application security.

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4 How to encrypt HTML5 local storage data?

Protecting HTML5 local storage data can be done by encrypting it before storing it on the user's browser. This can prevent unauthorized access or modification of the data, even if the user's browser is compromised or the data is leaked. However, encryption adds complexity and overhead to your web application, so you must carefully consider the benefits and costs of this approach. To encrypt HTML5 local storage data, you must choose a strong encryption algorithm and secure key management system, such as CryptoJS or Web Crypto API. Additionally, you must also encrypt and decrypt the data on the client-side using JavaScript before storing it in HTML5 local storage and using it in your web application.

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Islati Sk

Director & Founder; Software Engineer & Developer
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To HTML5 local storage data, choose a strong encryption algorithm, generate and manage encryption key securely, encrypt the data on the client-side using JavaScript, and decrypt it when needed. Consider trade-offs between security and performance, and implement additional security measures to protect the encryption key.

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5 How to limit the scope and duration of HTML5 local storage data?

To protect HTML5 local storage data, you should limit its scope and duration. For example, use sessionStorage instead of localStorage if you only need the data for the user's session. This will delete the data when the user closes the browser tab or window. Additionally, you can use origin-specific storage to store the data for a specific subdomain or protocol. HTML5 local storage is scoped by origin, meaning that it is only accessible by web pages with the same protocol, domain, and port. Finally, you can set expiration dates or time-to-live values for the data. JavaScript can be used to check the expiration date or time-to-live value of the data and delete it from HTML5 local storage when it is no longer valid. This will prevent outdated or irrelevant data from accumulating on the user's browser.

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Islati Sk

Director & Founder; Software Engineer & Developer
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To limit the scope and duration of HTML5 local storage data: Use sessionStorage for session-specific data that should be deleted when the browser is closed. Utilize origin-specific storage to restrict access to data from specific subdomains or protocols. Set expiration dates or time-to-live values for the data and delete it when it becomes invalid. These measures help protect user privacy and prevent the accumulation of outdated or irrelevant data.

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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Daniel King - CISSP CEH

I help companies secure their critical applications | Led the AWS Penetration Testing Division | Application Security Expert
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Don't store any sensitive data in local storage especially authentication or authorization data. Encoding, encrypting, or hashing doesn't protect your data. For example, you store an encrypted access token in local storage to authorize access. After an attacker gains access to your data in local storage data, they will access the URL of your app, add the key/encrypted token value via Dev Tools, refresh the app and access your app. The app is reading the encrypted value and decrypting it. It's the same as a pass the hash attack once they have the value. For an attacker to access local storage they only need physical access to machine/browser, XSS, or vulnerable JavaScript.

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How can you use HTML5 local storage safely?

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1 What is HTML5 local storage?

2 What are the security risks of HTML5 local storage?

3 How to prevent XSS attacks on HTML5 local storage?

4 How to encrypt HTML5 local storage data?

5 How to limit the scope and duration of HTML5 local storage data?

6 Here’s what else to consider

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