An XSS bug was found in United Airlines by Strukt and Burelogic (full article here). Apparently they were using this to protect from XSS:

Basically, the code overrides the native alert(), confirm(), prompt(), unescape(), and document.write()functions and nullifies them, so calling them does absolutely nothing. This was implemented as an "XSS protection".

I was wondering if using a base tag to point to a js file with a simple XSS payload would be blocked by the same function that blocked the XSS in the first place.

  • You can't import JS with base, you would need script. Or are you suggesting that you should set base href to a domain that you control, and then host the code without the XSS protections there? – Anders Nov 19 '17 at 11:27

The CSP will block your JS from a third party website. However, in the event that you manage to find a CSP bypass, XSSObject.proxy will override those functions anyway, because a javascript src runs on the page it is called.

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