Summary

In SvelteKit 2 sending a GET request with a body eg {} to a SvelteKit app in preview or with adapter-node throws Request with GET/HEAD method cannot have body. and crashes the app.

node:internal/deps/undici/undici:6066
          throw new TypeError("Request with GET/HEAD method cannot have body.");
                ^

TypeError: Request with GET/HEAD method cannot have body.
    at new Request (node:internal/deps/undici/undici:6066:17)
    at getRequest (file:///C:/Users/admin/Desktop/reproduction/node_modules/@sveltejs/kit/src/exports/node/index.js:107:9)
    at file:///C:/Users/admin/Desktop/reproduction/node_modules/@sveltejs/kit/src/exports/vite/preview/index.js:181:26
    at call (file:///C:/Users/admin/Desktop/reproduction/node_modules/vite/dist/node/chunks/dep-9A4-l-43.js:44795:7)
    at next (file:///C:/Users/admin/Desktop/reproduction/node_modules/vite/dist/node/chunks/dep-9A4-l-43.js:44739:5)
    at file:///C:/Users/admin/Desktop/reproduction/node_modules/@sveltejs/kit/src/exports/vite/preview/index.js:172:6
    at call (file:///C:/Users/admin/Desktop/reproduction/node_modules/vite/dist/node/chunks/dep-9A4-l-43.js:44795:7)
    at next (file:///C:/Users/admin/Desktop/reproduction/node_modules/vite/dist/node/chunks/dep-9A4-l-43.js:44739:5)
    at file:///C:/Users/admin/Desktop/reproduction/node_modules/@sveltejs/kit/src/exports/vite/preview/index.js:211:27
    at call (file:///C:/Users/admin/Desktop/reproduction/node_modules/vite/dist/node/chunks/dep-9A4-l-43.js:44795:7)

Node.js v20.11.0

TRACE requests will also cause the app to crash. Prerendered pages and SvelteKit 1 apps are not affected.

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PoC

<!-- _Complete instructions, including specific configuration details, to reproduce the vulnerability._ -->

First do a fresh install of SvelteKit 2 with the example app. Typescript.

1. npm run build
2. npm run preview

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