Sniffing browser history using HSTS
JavaScript Python HTML Shell
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Sniffly2 is a variant of Sniffly which abuses HTTP Strict Transport Security headers and the Performance Timing API in order to sniff your browsing history in Chromium-based browsers.


Visit in Chrome/Chromium/Brave/etc. with HTTPS Everywhere disabled.


  • does not work on mobile or Firefox
  • does not work over HTTPS due to mixed content blocking.
  • adblockers may taint results


  • crbug436451, reported by, for the idea of probing port 443 over HTTP
  • Scott Helme for providing an initial list of HSTS hosts