Affected: Maven: io.netty:netty-codec-http

## Summary A flaw in netty's parsing of chunk extensions in HTTP/1.1 messages with chunked encoding can lead to request smuggling issues with some reverse proxies.

## Details When encountering a newline character (LF) while parsing a chunk extension, netty interprets the newline as the end of the chunk-size line regardless of whether a preceding carriage return (CR) was found. This is in violation of the HTTP 1.1 standard which specifies that the chunk extension is terminated by a CRLF sequence (see the [RFC](https://datatracker.ietf.org/doc/html/rfc9112#name-chunked-transfer-coding)).

This is by itself harmless, but consider an intermediary with a similar parsing flaw: while parsing a chunk extension, the intermediary interprets an LF without a preceding CR as simply part of the chunk extension (this is also in violation of the RFC, because whitespace characters are not allowed in chunk extensions). We can use this discrepancy to construct an HTTP request that the intermediary will interpret as one request but netty will interpret as two (all lines ending with CRLF, notice the LFs in the chunk extension):

``` POST /one HTTP/1.1 Host: localhost:8080 Transfer-Encoding: chunked

48;\nAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA\n0

POST /two HTTP/1.1 Host: localhost:8080 Transfer-Encoding: chunked

0

```

The intermediary will interpret this as a single request. Once forwarded to netty, netty will interpret it as two separate requests. This is a…