Snow is the most advanced open sourced tool for securing same origin realms in runtime browser apps - secured and easy to use:

• Include Snow in your web app's loading html file (or by requiring it as a module):

<script src="https://unpkg.com/@lavamoat/snow/snow.prod.js"></script>

• Pass Snow a callback and Snow will invoke it with every new window object in runtime!

SNOW( win => console.log('New window detected:', win) )

About

Snow is an experimental ⚠️ tool coming in the form of a JavaScript shim that once is applied to the page exposes an API that when is provided with a callback, will make sure to call it with every new window that is being injected to DOM, before its creator gets a hold on it.

This ability exists for extensions (with the all_frames: true property), but Snow brings it to non extension javascript with the same privileges as the web app.

Read more about Snow and the motivation behind it here

🚨 IMPORTANT UPDATE 🚨

Starting Version 2.0.1 Snow officially doesn't support vulnerabilities that can be protected against by disallowing unsafe-inline completely and by correctly using the object-src directive to not allow self.

• To learn more why is that, see section 4.

In addition, Snow "stops playing nice" - operations that are considered insecure will be intercepted and cause Snow to throw an exception. This is part of the realization we reached as part of the work on Snow, where "nice security" leaves Snow vulnerable, and true security can only be shipped with a more "aggresive" approach.

• To learn more why is that, see #133.

Demo - The Snow Challenge! 🏆

Snow's challenge is the easiest way to graspe the power of Snow.

Here we have a serverless demo app, which installs and uses Snow to disable the functionality of the alert function for all same origin realms.

In other words, the app uses Snow to make sure no one can call the alert function, not even when:

• Trying to create an <iframe> and use its inner window's alert;
• Trying to call the alert function from the console (even self-XSS won't help you!);
• Trying to open a new tab and use its alert.

Hence, the rulls are very simple - visit the app and pop an alert! 😉

If you manage to bypass Snow and pop an alert message - help us by opening an issue so we could continue to improve Snow's security!

Usage

// API
SNOW(cb = (win) => { /* LOGIC */ });


// example, disable alert API in the webpage completely
SNOW((win) => {
    win.alert = (msg) => {
        console.log('alert is disabled! msg is: ' + msg);
    };
});

Install

The latest snow production version is included in the official repo and also in upkg cdn, so in order to install snow in the website, simply place it wherever and serve it to the website as-is:

<script src="https://unpkg.com/@lavamoat/snow/snow.prod.js"></script>

After this line, window should expose window.SNOW API for the rest of the scripts in the website to use.

Not like standard third party libraries, snow has special requirements (security-wise) in order for it to play its role securely.

👇 It is highly important to be aware of them when integrating Snow into an app to gain full security - READ CAREFULLY 👇:

1. It has to run as the first piece of javascript that runs in the webpage - otherwise any other javascript code will have the ability to bypass snow and cancel its purpose completely (that's why snow can never overpower extensions). In order to achieve that, when loading via a script tag it must load script synchronously (do not use async=true!).

2. It has to be served as-is - If it goes through any bundlers that might change it, the modified version might contain flaws that attackers might use to cancel its effect (for further explanation see natives section).

3. Snow needs to be set and called in every HTML page served from your web app - Even though this is the attack vector Snow tries to protect the app against, there are types of attacks Snow won't be able to defend against (which is why we want Snow to become a native browser feature so bad!). This mainly refers to the #73 discovery. The only way to defend the app against such an attack it to make sure all HTML files served by the app load Snow themselves. Does this make Snow useless? No - there are planty other types of attacks Snow defends your app against.

4. Most importantly, it's highly vulnerable without minimal help from CSP - As of version 2.0.1 the project will seize to attempt to defend against vulnerabilities that aren't possible to exploit when (a) unsafe-inline isn't allowed and (b) object-src to self isn't allowed. This is because (a) defending against string-JS attacks is basically an endless task and probably impossible, and (b) object/embed elements behaviour is also too unpredictable while these elements shouldn't be even used in the first place. Snow will do its best regardless of what CSP is applied - use at your own risk!

   • please learn more about this ☝️ at #118 & #133

SNOW API can also be required as part of a bundle instead of a script tag:

yarn add @lavamoat/snow

const snow = require('@lavamoat/snow');

Contribute

This project is an important POC aspiring to standardize how windows should be hermetically handled, however it is not yet production ready.

snow eventually is a shim that comes to both demonstrate and utilize the API we wish to see builtin to browsers in the future. Until snow becomes a platform builtin API, we have to attempt to overcome several challenges that are significantly harder to do so in pure javascript:

Support

snow supports Chrome, Firefox, Safari and all other Chromium based browsers (Opera, Edge, Brave, etc).

Performance

Achieving a hermetic solution costs in performance. Injecting this script into some major websites went smoothly while with some others it caused them some performance issues.

Security

Although this project takes the hermetic concept very seriously and massively tests for potential flaws, snow might potentially still have flaws which might enable attackers to bypass its hooks.

Bottom line - snow might have security vulnerabilities!

Hopefully in the future snow will become a builtin API provided by the browser. Achieving that goal will allow security assurance - such functionality will be safer to implement on behalf of the browser rather than the web app.

Tests

In order to assure security, there are many tests that verify that snow is fully hermetic as promised - everything that snow supports is fully tested.

The tests mainly try to bypass snow in any possible way.

If you found a vulnerability in snow, open a PR with a test that demonstrates it (or just let us know, and we'll do it).

Help

Help with promoting any of the topics above is very much appreciated in order for this project to become production ready and reshape how hermetic window hooking should look like!

Troubleshooting

In log.js file you can find references to issues you might encounter using snow. If you do, you should see an error/warning thrown to console in your application with a reference to the relevant issue thread.

In each thread a discussion around the issue is being made in order to better solve it, so please share your experience with the issue in order for us to solve it in the best way possible.

If you encounter an issue that is not being handled by snow correctly, please open a new one.

Supporters

Funded by Consensys 💙

Maintained and developed by MetaMask 🦊

Part of the LavaMoat 🌋 Javascript security toolbox

Invented and developed by Gal Weizman 👋🏻