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Interview question · Application & API Security

Does a Content Security Policy stop DOM-based XSS?

A strict CSP blocks many XSS payloads but not all, and DOM XSS has paths it cannot see. The scored answer explains what a nonce-based policy stops, where it fails, and why Trusted Types targets the DOM sinks.

mediumNewPreparation tags: Google, Microsoft, MetaUpdated Nov 2026

A strict CSP blocks many XSS payloads but not all, and DOM XSS has paths it cannot see. The scored answer explains what a nonce-based policy stops, where it fails, and why Trusted Types targets the DOM sinks.

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  1. 01 State the assumptions your answer depends on.
  2. 02 Explain the mechanism and choose a control.
  3. 03 Name a condition that would change your decision.

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What if · the follow-ups in this answer

The answer works through 6 follow-ups like an interviewer would

A single-page app has a strict, nonce-based Content Security Policy, and a tester reports a DOM XSS finding where URL fragment data reaches innerHTML.

  1. What does a strict CSP stop?
  2. What does it not stop?
  3. Should the finding be fixed anyway?
  4. How do Trusted Types help?
  5. How do you keep the CSP strong?
  6. How would you respond to the finding?

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