Unescaped error message included on error page in SvelteKit

Vulnerability Description

SvelteKit is a framework for rapidly developing robust, performant web applications using Svelte. The static error.html template for errors contains placeholders that are replaced without escaping the content first. error.html is the page that is rendered when everything else fails. It can contain the following placeholders: %sveltekit.status% — the HTTP status, and %sveltekit.error.message% — the error message. This leads to possible injection if an app explicitly creates an error with a message that contains user controlled content. Only applications where user provided input is used in the `Error` message will be vulnerable, so the vast majority of applications will not be vulnerable This issue has been addressed in version 2.8.3 and all users are advised to upgrade. There are no known workarounds for this vulnerability.

References

• https://github.com/sveltejs/kit/security/advisories/GHSA-mh2x-fcqh-fmqv
• https://github.com/sveltejs/kit/commit/134e36343ef57ed7e6e2b3bb9e7f05ad37865794
• https://kit.svelte.dev/docs/errors