NPM package apollo-server-core version 2.0.0 through 2.25.2, and 3.0.0 through 3.4.0 are imacted. Fixed in 2.25.3 and 3.4.1. In certain configurations, Apollo Server serves the client-side web app "GraphQL Playground" from the same web server that executes GraphQL operations. This web app has access to cookies and other credentials associated with the web server's operations. There is a cross-site scripting vulnerability in GraphQL Playground that allows for arbitrary JavaScript code execution in your web server's origin. If a user clicks a specially crafted link to your GraphQL Playground page served by Apollo Server, an attacker can steal cookies and other private browser data. Details of the underlying GraphQL Playground vulnerability are available in this graphql-playground advisory. (A similar vulnerability exists in the related graphiql project.) This advisory focuses on identifying whether Apollo Server installations are vulnerable and mitigating the vulnerability in Apollo Server; see the other advisories for details on the XSS vulnerability itself. The impact of this vulnerability is more severe if (as is common) your GraphQL server's origin URL is an origin that is used to store sensitive data such as cookies. In order for this vulnerability to affect your Apollo Server installation, it must actually serve GraphQL Playground. The integration between Apollo Server and GraphQL Playground is different in Apollo Server 2 and Apollo Server 3. You can tell which version of Apollo Server you are running by looking at the version of the package from which you import the ApolloServer class: this may be apollo-server, apollo-server-express, apollo-server-lambda, etc.