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JS security

Best practices for JS security

1. Check regularly for npm package security issues

npm audit // shows vulnerable packages

2. Implement eslint security rules
for example :eslint-plugin-security

3. Use best practices

4. JWT vs servers-side sessions
JWTs provide a means of maintaining session state on the client in stead of doing it on the server.
With server-side sessions you will either have to store the session identifier in a database, or else keep it in memory and make sure that the client always hits the same server. Both of these have drawbacks. In the case of the database (or other centralised storage), this becomes a bottleneck and a thing to maintain – essentially an extra query to be done with every request.
With an in-memory solution you limit your horizontal scaling, and sessions will be affected by network issues (clients roaming between Wifi and mobile data, servers rebooting, etc)
Moving the session to the client means that you remove the dependency on a server-side session, but it imposes its own set of challenges.
- Storing the token securely
- transporting it securely
- JWTs Sessions can sometimes be hard to invalidate.
- Trusting the client’s claim.
These issues are shared by JWTs and other client-side session mechanisms alike.
JWT in particular addresses the last of these. It may help to understand what a JWT is:
It is a bit of information. For user sessions you could include the username and the time when the token expires. But it could conceivably be anything, even the session ID or the user’s entire profile. (Please don’t do that though) It has got a secure signature that prevents malicious parties from generating fake tokens (You need access to the server’s private key to sign them and you can verify that they were not modified after they were signed) You send them with every request, just like a cookie or Authorization Header would be sent. In fact they are commonly sent in the HTTP Authorization header but using a cookie is fine too.
The token is signed and so the server can verify its origin. We will assume that the server trusts its own ability to sign securely (you should use a standard library: don’t try to do it yourself, and secure the server properly)
On the issue with securely transporting the token the answer is commonly to send it via an encrypted channel, usually httpS.
Regarding securely storing the token in the client, you need to ensure that the bad guys can’t get to it. This (mostly) means preventing JS from bad web sites from reading the token to send it back to them. This is mitigated using the same strategies used to mitigate other kinds of XSS attacks.
If you have a need to invalidate JWTs there are definitely ways this can be achieved. Storing a per-user epoch for only users who have requested to have their “other sessions terminated” is a very efficient method that will probably be good enough. If a application needs per-session invalidation, then a session ID can be maintained in the same way and the “killed tokens” table can still be maintained to be much smaller than the full user table (You only need to retain records newer than the longest allowed token lifetime.) So the ability to invalidate the token partially negates the benefit of client-side sessions in that you would have to maintain this session killed state. This will more than likely be a much smaller table than the original session state table, so the lookups are still more efficient though.
One other benefit of using JWT tokens is that it is reasonably easy to implement using libraries available in probably every language you can expect to have it. It is also completely divorced from your initial user authentication scheme – if you move to a finger print based system you do not need to make any changes to the session management scheme.
A more subtle benefit: Because the JWT can carry “information” and this can be accessed by the client you can now start do some smart things. For example remind the user that their session will be expiring a few days before they are logged out, giving them the option to re-authenticate, based on the expiry date in the token. Whatever you can imagine.
So in short: JWTs answers some of the questions and shortcomings of other session techniques.
1. “Cheaper” authentication because you can eliminate a DB round trip (or at least have a much smaller table to query!), which in turns enable horizontal scalability.
2. Tamper-proof client-side claims.
While JWTs does not answer the other issues like secure storage or transport, it does not introduce any new security issues.
A lot of negativity exists around JWTs but if you implement the same security that you would for other types of authentication, you will be fine.
One final note: It is also not Cookies vs Tokens. Cookies is a mechanism for storing and transporting bits of information and can be used to store and transport JWT tokens too.

A few years ago, before the JWT revolution, a <token> was just a string with no intrinsic meaning, e.g. 2pWS6RQmdZpE0TQ93X. That token was then looked-up in a database, which held the claims for that token. The downside of this approach is that DB access (or a cache) is required everytime the token is used.

JWTs encode and verify (via signing) their own claims. This allows folks to issue short-lived JWTs that are stateless (read: self-contained, don’t depend on anybody else). They do not need to hit the DB. This reduces DB load and simplifies application architecture because only the service that issues the JWTs needs to worry about hitting the DB/persistence layer (the refresh_token you’ve probably come across).

5. Prevent against CSRF attacks with CORS: control allow origin

 res.set('Access-Control-Allow-Origin', '*');

5. Prevent against XSS (Cross site scripting)  attacks:

React library performs escaping logic components via the render method.  Only worry about excaping in following cases:

  • Do not use dangerouslySetinnerHtml and if you do, escape the values
  • Props are not validated, sanitized, or contextually escaped when they are passed to React.createElement; they are later added to the DOM by ReactDOM.render as attributes on elements, rather than text content. Some HMTL attributes allow you to inline javascript protocol-based links that execute JavaScript in the context of the current page. These handlers will be added to the page if you don’t handle them with custom code in your React components.
  • If you are styling your React Components using CSS-in-JS libraries like styled-components and glamorous, then ReactDOM.render does not escape the values you pass into the CSS. Attackers who can control the value of CSS properties passed in as props can inject malicious CSS and install key loggers and other tools in your users’ browsers.

Useful links:
Best practices security JS
Security best practices
ciper suites

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