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I was testing a website which does not have XSS in their scope. So I thought it would be a good idea to escalate XSS to a bug which is valid. I need to make a request to my server but the problem is closing tag > or forward slashes / are escaped but everything else works. The event handlers also work.

Is there way to call javascript file externally from these event handlers so that I can execute script?

Actually I want to inject third part js file without script tag or any tag which closes.

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  • Welcome to the community. Your question is a bit unclear to me on what you want to achieve exactly. Inject 3rd party JS files or what? Aug 17, 2022 at 15:16
  • Please clarify your specific problem or provide additional details to highlight exactly what you need. As it's currently written, it's hard to tell exactly what you're asking.
    – Community Bot
    Aug 17, 2022 at 15:16

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If you have any injection sites within the following locations, the restrictions mentioned are not enough to prevent XSS:

  • Within an HTML element tag, e.g. as an HTML attribute value. You can end one attribute and start a new one, including event handlers and so on.
  • Within a script block. No need to provide the closing (or opening!) script tags if you're already between valid ones.

Additionally, if you check the client-side script, you might find opportunities for DOM-based XSS (where client script takes some user-controlled input and treats it as code, either by injecting it directly into the DOM without suitable escaping, or executing it as code e.g. via JS eval).

However, the mitigation you've described (why do you think the site "does not have XSS in their scope", given that they've implemented this obviously-anti-XSS measure?) is sufficient to prevent adding your own complete HTML elements or breaking out of HTML comments or CDATA sections (although those are XML/XHTML and not HTML constructs and thus rarely seen in modern sites). Without that, you won't be able to get stored or reflected XSS unless you can find an injection point that isn't just in the document body (specifically, one that satisfies the above bullet points) or an injection point where this escaping isn't performed.

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