At first, I attempted to Base64-encode a minified version of this JavaScript and include it within the onerror event of the XSS payload. It would then be decoded and executed using eval(atob()), as shown below:

The sentence is from How I Built An XSS Worm On Atmail. I have met this one serveral time. I can't understand this well. Here I know that the author is assuming that he tried to build xss payload, then the result may be like what he think instead of the reality. Therefore, What's phrase 'It would then be' mean? What's the meaning of word then here?

  • After I tried to encode the script in base 64 and insert it into the payload event, the script went along at that point (would then) get translated out of base 64 and on to running under the eval module. – Yosef Baskin Jun 25 '17 at 20:05

This is a kind of "future in the [hypothetical] past". It corresponds to "It will then be decoded" in the present.

So the writer is saying "If I had succeeded in ..., it would then ["next"] be decoded ... "

  • The author might have phrased it more clearly as "It would then have been decoded..." to be hypothetical past. – Chemus Jun 25 '17 at 20:09
  • @Chemus: it could have "have been", but it doesn't need to. I don't fnd that any clearer. – Colin Fine Jun 25 '17 at 20:11
  • That's true, hence my phrasing as 'might have been...' – Chemus Jun 25 '17 at 20:13

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