Description

Netty: Memory Exhaustion via HTTP/3 Reserved Frame Types

Summary

Netty's Http3FrameCodec buffers incoming data for HTTP/3 reserved frame types up to the specified payload length without any limits. The payload length is read directly from the wire and trusted without validation. A bad actor can send a reserved frame with a payload length of up to Integer.MAX_VALUE, causing the server to buffer the data in memory. This leads to an OOM and a gradual Denial of Service due to memory exhaustion as multiple streams are opened.

Details

io.netty.handler.codec.http3.Http3FrameCodec#decodeFrame handles reserved frame types as follows:

                // Handling reserved frame types
                // https://tools.ietf.org/html/draft-ietf-quic-http-32#section-7.2.8
                if (in.readableBytes() < payLoadLength) {
                    return 0;
                }

The payLoadLength is read directly from the wire and trusted implicitly. Since payLoadLength can be up to Integer.MAX_VALUE and there is no maximum payload length enforcement for reserved frames, the decoder will accumulate bytes in memory until the wire-provided length is reached.

This allows a bad actor to exhaust server memory by opening multiple QUIC streams and sending reserved frames with large payload lengths, followed by a small amount of data (e.g., up to the defined limit) on each stream.

PoC

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

Denial of Service due to gradual memory exhaustion. Any application using Netty's HTTP/3 codec is impacted.

Mitigation

Aliases

References