Cross-Site Scripting attack (XSS) on dev mode 404 page in SvelteKit

Vulnerability Description

SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. "Unsanitized input from *the request URL* flows into `end`, where it is used to render an HTML page returned to the user. This may result in a Cross-Site Scripting attack (XSS)." The files `packages/kit/src/exports/vite/dev/index.js` and `packages/kit/src/exports/vite/utils.js` both contain user controllable data which under specific conditions may flow to dev mode pages. There is little to no expected impact. The Vite development is not exposed to the network by default and even if someone were able to trick a developer into executing an XSS against themselves, a development database should not have any sensitive data. None the less this issue has been addressed in version 2.8.3 and all users are advised to upgrade.

References

• https://github.com/sveltejs/kit/security/advisories/GHSA-rjjv-87mx-6x3h
• https://github.com/sveltejs/kit/commit/d338d4635a7fd947ba5112df6ee632c4a0979438