DoH3 to cloudflare-dns.com yields HTTP 400 if GREASE http3 frame after DATA frame

What is the name of the domain?

What is the error number?

400

What is the error message?

Invalid query

What is the issue you’re encountering

“HTTP 400 Invalid query” for GREASE frames after DATA frames over DoH3

What feature, service or problem is this related to?

I don’t know

What are the steps to reproduce the issue?

When a DoH3 request (but likely reproduces for any HTTP3 request against cloudflare edge?) is performed through quinn or the quiche client PoC below
it seems like the received body is wrongly handled and a HTTP 400 Invalid query is returned.
Those specifically send GREASE frames after the body.
Therefore it could be that whatever cloudflare uses on top of quiche (?) handles GREASE frames after the body/DATA frames wrong.

Original issue: GREASE incompatible with Cloudflare · Issue #206 · hyperium/h3 · GitHub
Quiche Client PoC: Quiche Cloudflare Grease Post Body Bug Reproduce · GitHub

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