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/nodemodules/@sveltejs/kit/src/exports/node/index.js:107:9) at file:///C:/Users/admin/Desktop/reproduction/nodemodules/@sveltejs/kit/src/exports/vite/preview/index.js:181:26 at call (file:///C:/Users/admin/Desktop/reproduction/nodemodules/vite/dist/node/chunks/dep-9A4-l-43.js:44795:7) at next (file:///C:/Users/admin/Desktop/reproduction/nodemodules/vite/dist/node/chunks/dep-9A4-l-43.js:44739:5) at file:///C:/Users/admin/Desktop/reproduction/nodemodules/@sveltejs/kit/src/exports/vite/preview/index.js:172:6 at call (file:///C:/Users/admin/Desktop/reproduction/nodemodules/vite/dist/node/chunks/dep-9A4-l-43.js:44795:7) at next (file:///C:/Users/admin/Desktop/reproduction/nodemodules/vite/dist/node/chunks/dep-9A4-l-43.js:44739:5) at file:///C:/Users/admin/Desktop/reproduction/nodemodules/@sveltejs/kit/src/exports/vite/preview/index.js:211:27 at call (file:///C:/Users/admin/Desktop/reproduction/nodemodules/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.

<!-- Details Give all details on the vulnerability. Pointing to the incriminated source code is very helpful for the maintainer. --> 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 3. Go to http://localhost:4173 (works) 4. curl -X GET -d "{}" http://localhost:4173/bye 5. Application crashes and http://localhost:4173 is down

Impact <!-- What kind of vulnerability is it? Who is impacted? --> Denial of Service for apps using adapter-node