H3 is a minimal H(TTP) framework built for high performance and portability. Prior to 1.15.5, there is a critical HTTP Request Smuggling vulnerability. readRawBody is doing a strict case-sensitive check for the Transfer-Encoding header. It explicitly looks for "chunked", but per the RFC, this header should be case-insensitive. This vulnerability is fixed in 1.15.5.

Affected: npm: h3

I was digging into h3 v1 (specifically v1.15.4) and found a critical HTTP Request Smuggling vulnerability.

Basically, `readRawBody` is doing a strict case-sensitive check for the Transfer-Encoding header. It explicitly looks for "chunked", but per the RFC, this header should be case-insensitive.

**The Bug**: If I send a request with Transfer-Encoding: ChuNked (mixed case), h3 misses it. Since it doesn't see "chunked" and there's no Content-Length, it assumes the body is empty and processes the request immediately.

This leaves the actual body sitting on the socket, which triggers a classic TE.TE Desync (Request Smuggling) if the app is running behind a Layer 4 proxy or anything that doesn't normalize headers (like AWS NLB or Node proxies).

**Vulnerable Code** (`src/utils/body.ts`):

```js if ( !Number.parseInt(event.node.req.headers["content-length"] || "") && !String(event.node.req.headers["transfer-encoding"] ?? "") .split(",") .map((e) => e.trim()) .filter(Boolean) .includes("chunked") // <--- This is the issue. "ChuNkEd" returns false here. ) { return Promise.resolve(undefined); } ```

I verified this locally:

- Sent a `Transfer-Encoding: ChunKed` request without a closing 0 chunk. - Express hangs (correctly waiting for data). - h3 responds immediately (vulnerable, thinks body is length 0).

**Impact**: Since H3/Nuxt/Nitro is often used in containerized setups behind TCP load balancers, an attacker can use this to smuggle reque…