The Snyk Advisor website (https://snyk.io/advisor/) was vulnerable to a stored XSS prior to 28th March 2023. A feature of Snyk Advisor is to display the contents of a scanned package's Readme on its package health page. An attacker could create a package in NPM with an associated markdown README file containing XSS-able HTML tags. Upon Snyk Advisor importing the package, the XSS would run each time an end user browsed to the package's page on Snyk Advisor.
CWE-79, CWE-79