I built FoxIO's 54 KB HTTP/3 accordion by hand. aioquic's decoder unfolded it to 200 MB.

FoxIO disclosed QPACK amplification attacks against HTTP/3 (7 of 10 stacks, up to 4,000x on Bun; aioquic unpatched). I hand-crafted the encoder-stream bytes against the exact decoder aioquic builds by default: 54,009 wire bytes decoded to 50,000 fields / 200,500,000 bytes (3,712x), no error, no cap — and aioquic's MAX_FIELD_SECTION_SIZE constant is defined but never sent or enforced.