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Bypassing Chrome's CORB Feature

I'm trying to load some external JavaScript, but Chrome isn't having it.
To be clear, I'm using a bookmarklet to create a new script element, change the src attribute to my source code, and then append it to the header.
Here's the code:
javascript:var script=document.createElement("script");script.src="URL";document.getElementsByTagName('head')[0].appendChild(script);
Unfortunately, Chrome's Cross-Origin Read Blocking algorithm is preventing me from injecting the source into the header. I believe that this is due to the fact that said source document is simply plain text, and not an acceptable JavaScript file.
Is there any workaround for this?

There are many websites that because of CSP (Content Secrutiy Policy) not let you load scripts from other URLS. You should check the CSP headers of the website you trying to inject scripts into.
More info on CSP:
https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP
UPDATE
I see that your edit your question (after my initial answer) and now your asking specific about CORB issue. In that case you have to ensure that your script returing the correct content-type header. If you script doens't return text/javascript chrome will not execute it.
How do you serve the JavaScript file? if you will give more details we can try to help.
Usually servers are giving the correct header to JS files. There are some exception. For e.g. when user upload JS file to GitHub, GitHub will serve it without the content type header. This is because they don't want that a webmaster that trust only GitHub will have a risk that a user will execute user uploaded script (to GitHub) on his website.
More info:
https://www.chromium.org/Home/chromium-security/corb-for-developers

jQuery .load() with Relative Path - XMLHttpRequest Cannot Load - Workaround?

I have a locally-stored project whose directory structure is the following (I minimized non-relevant folders):
What I want to do is that in an HTML file, like index.html, to add a <header> such that its contents would be loaded from an external HTML file, so all of what I'll have to write in index.html would be <header>, and my solution would load the content automatically.
To do this, I'd like to use JavaScript (preferably jQuery, but I'll accept other solutions if they work and jQuery doesn't, or if they work and executed faster than jQuery).
I don't think that I should use an <iframe> due to the fact that it'd probably increase loading times more than using jQuery/JavaScript (which, like I said, is what works now, when the website is live).
Right now, I'm using the jQuery .load() function. I don't know much about jQuery, but I've been told that it should work locally - and it doesn't, for me.
My browser's console shows me the problem:
jquery-3.1.1.min.js:4 XMLHttpRequest cannot load file:///C:/Users/GalGr/Desktop/eiomw/header.html. Cross origin requests are only supported for protocol schemes: http, data, chrome, chrome-extension, https, chrome-extension-resource.
And I'm trying to overcome it.
This code works on my live website - it might not be updated to the code of the files that I linked to below, but it doesn't matter - their code matters.
This is the index.html file:
index.html
This is the header.html file:
header.html
This is `main_script.js:
main_script

The reason you're having a problem with this locally is mainly down to security measures in your browser.
Essentially whenever you're using jQuery's load() function it makes a separate HTTP request (approach known as AJAX) for the file or URL you give it.
Modern browsers enforce that the URL you request using AJAX methods is from the same origin (server) as a security feature to stop pages randomly loading content from anywhere on the internet in the background. In your case it seems like this shouldn't affect you because you're browsing your pages locally and the request you're making using load() is also for a local file (header.html).
However, I am assuming you're just opening up the page directly in your browser, so your browser's URL will look something like 'file:///C:/Users...' (similar example in the error message you gave). This means your browser is directly reading the file from disk and interpreting it as HTML to display the page. It seems likely you don't actually have a local HTTP server hosting the page, otherwise the URL would start with 'http://'. It is for this reason that the browser is giving the security error, even though your AJAX request for header.html is technically from the same source as the page it is executed on.
Your server will have an HTTP server which it's using to host the pages, and so everything works fine as you're then using HTTP as normal, and this security feature does not get in your way.
I would suggest that you simply install an HTTP server locally on your dev machine. You don't even need to 'install' one per-se, there are loads of development HTTP servers that just run standalone, so you start them up when you want to browse your local HTML files. As you appear to be on Windows, I'd check out either IIS (Windows' HTTP server) or IIS Express (like IIS but runs standalone). There are also many others available like Apache, Nginx, etc. etc.
If you do this, you can host your pages on something like 'http://localhost/index.html'. Then, any AJAX requests you make for local files will work fine, just like your server.
Hope that makes sense, and I'm not telling you something you already know?

Why not using something more straight foreword like mustache.js ?

I found a solution:
Using phpStorm's built-in localhost, I was able to emulate a server that handles my requests and responses.

Avoid cryptic javascript "script error" using cdn

I'm using a script that detects Javascript errors and reports them to my backend. However I am getting cryptic "script error" messages, which is not very helpful for debugging.
According to Cryptic "Script Error." reported in Javascript in Chrome and Firefox the reason is because the script that threw the error is served from a different origin than my site.
Since I'm using a CDN all of my scripts are effectively served from another domain. Is there a way to get more useful error messages while still using a CDN?
Also everything is served over SSL so I would like to retain this ability.

I had a similar problem: my scripts are served by a subdomain and fall under the same origin restriction. However, I solved this by:
1) adding every script tag like this:
<script type="text/javascript" src="http://subdomain.mydomain.tld" crossorigin="*.mydomain.tld" />
2) modifying the apache httpd.conf by adding the following inside every vhost (you must enbable mod_headers):
<IfModule mod_headers.c>
Header add Access-Control-Allow-Origin "*.mydomain.tld"
</IfModule>
On one of my server I was not able to make this functional except by replacing
*.mydomain.tld
by
*
Be aware of the flaws with potentially allowing * to phish extended information. Documentation on CORS, same-origin, img & fonts, cdn is available but very fewer about script tag crossorigin details is available.
Hope this helps ...

Try using jsonp for the dataType attribute in jQuery.ajax. The remote server will also need to support jsonp. It will get around the browser security preventing XSS.
Alternatively, you could use an IFrame and use jQuery within each window, but use HTML5 postMessage to communicate back and forth between the windows on two different domains.
Or, if you control both servers you can set the headers for same origin.
Jsonp has been my weapon of choice for this kind of problem. The others are just a legitimate.

Mixed Content Warning IE: What matters; css, images, everything?

I have just moved my site from http to https and IE-9 started showing non-secure content warning at home page. This warning is understandable because i have one http call to googleapi for getting jquery script. But when I login and enter the inner pages there is no warning from IE despite the fact that most of the images are coming from other servers through http protocol.
So the question: Is getting image over http is fine when accessing site over https? Does only css and js matters? or shall I have to get all the data through HTTPS? If so how is my scenario justifiable (getting images over http from other server on https page without warning)?

If you load CSS and JS over HTTP then an attacker can inject executable code. Unfortunately IE will execute JavaScript within CSS. The problem with loading images over HTTP from the same domain is that the browser will likely spill the session id in plain text which is a violation OWASP a9.

You can use the protocol-relative URL on all your urls to avoid this issue in IE.
Basicaly, instead of linking to a js/image/css by using its full path with the protocol, you instead link to it by leaving out the protocol bit and just using a double slash, //.
This will have the effect of all the above links inheriting the protocol from the parent page.
Of course this depends on you having valid SSL certs on the domains you're serving the different files form.
One other thing to note also is that images in your pages or CSS that are done using data URI could also cause mixed content warnings in IE.
To find out what files are causing issues, I recommend using Fiddler
There is also another tool that a fellow SO user, Eric Law wrote:
Install it from http://www.bayden.com/dl/scriptfreesetup.exe and you will get a different mixed content prompt which shows the exact URL of the first insecure resource on the page. That tool is basically a prototype and you should uninstall it when you're done with it. It works on IE8 and you should install it as admin.

JavaScript and CouchDB - How do I avoid cross-origin policy errors on GET/POST/PUT/DELETE requests

I am posting this question on Super User as well. In my opinion this question overlaps the two...
I am creating a simple JavaScript wrapper for CouchDB's REST-ful interface, but I am stuck on same-origin policy issues.
So far I've been developing my code to work locally - and only as a proof of concept - on Mozilla FireFox. My server is running on localhost, port 5984.
To disable cross-origin policy in Mozilla FireFox you can use the PrivilegeManager, but it only gets me half-way in the sense that I can't do PUT requests against my server...
/*
* Including this in my JavaScript file only seems to disable cross-origin
* policy checks for POST and GET requests in Mozilla FireFox.
* PUT requests fail.
*/
netscape.security.PrivilegeManager.enablePrivilege(
"UniversalBrowserRead UniversalBrowserWrite"
);
Is there any way that I can configure my server to hide it's location so I won't have to implement browser-specific work-arounds to avoid same-origin policy issues? If not: what browser work-arounds exist to disable same-origin policy completely?

Unfortunately, any browser workarounds to disable same-origin policies are likely to be treated as serious security bugs and fixed as soon as possible.
See if you can come up with a way to work within the same-origin policy without trying to bypass it.
Can you serve your example scripts on the target server? Could you build a reflection script that would load the target script on your server after a local script on the users computer uploaded whatever they modified?
There should be a good solution that doesn't involve bypassing the same-origin policy. Trying to hack your way around it is a good way to ensure that your code doesn't work properly in future browsers.

I strugled with that issue too, trying to run automated tests on a local html file connecting to a virtualized CouchDB server, here's my solution:
I created a small implementation (and open sourced it) of the simplest solution when you can't enable CORS on the server,
you need to upload a .js and an .html file to the target server, (you can use any security mechanism to restrict access to this file if you want). Or you can change some simple parameters on the html file to restrict by domain.
On your page you use the same script to create an invisible iframe where the hosted .html is loaded, and proxy certain methods (sort-of RPC) thru that iframe using window.postMessage(), by default jQuery ajax methods can be proxied without extra configuration.
All this with one line of js code :)
FrameProxy at GitHub
(fell free to use it and fork it!)