CVE-2026-42584

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpClientCodec pairs each inbound response with an outbound request by queue.poll() once per response, including for 1xx. If the client pipelines GET then HEAD and the server sends 103, then 200 with GET body, then 200 for HEAD, the queue pairs HEAD with the first 200. The HEAD rule then skips reading that message’s body, so the GET entity bytes stay on the stream and the following 200 is parsed from the wrong offset. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

Summary

If HttpClientCodec is configured, there are use cases when a response body from one request, can be parsed as another's.

Details

HttpClientCodec pairs each inbound response with an outbound request by queue.poll() once per response, including for 1xx. If the client pipelines GET then HEAD and the server sends 103, then 200 with GET body, then 200 for HEAD, the queue pairs HEAD with the first 200. The HEAD rule then skips reading that message’s body, so the GET entity bytes stay on the stream and the following 200 is parsed from the wrong offset.

Prerequisites

• HTTP/1.1 pipelining
• HEAD in the pipeline
• The server sends 1xx

PoC

    @Test
    public void test() {
        EmbeddedChannel channel = new EmbeddedChannel(new HttpClientCodec());

        assertTrue(channel.writeOutbound(new DefaultFullHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.GET, "/1")));
        ByteBuf request = channel.readOutbound();
        request.release();
        assertNull(channel.readOutbound());

        assertTrue(channel.writeOutbound(new DefaultFullHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.HEAD, "/2")));
        request = channel.readOutbound();
        request.release();
        assertNull(channel.readOutbound());

        String responseStr = "HTTP/1.1 103 Early Hints\r\n\r\n" +
                "HTTP/1.1 200 OK\r\nContent-Length: 5\r\n\r\nhello" +
                "HTTP/1.1 200 OK\r\n\r\n";
        assertTrue(channel.writeInbound(Unpooled.copiedBuffer(responseStr, CharsetUtil.US_ASCII)));

        // Response 1
        HttpResponse response = channel.readInbound();
        assertEquals(HttpResponseStatus.EARLY_HINTS, response.status());
        LastHttpContent last = channel.readInbound();
        assertEquals(0, last.content().readableBytes());
        last.release();

        // Response 2
        response = channel.readInbound();
        assertEquals(HttpResponseStatus.OK, response.status());
        last = channel.readInbound();
        assertEquals(0, last.content().readableBytes());
        last.release();

        // Response 3
        FullHttpResponse response1 = channel.readInbound();
        assertTrue(response1.decoderResult().isFailure());
        assertEquals(0, response1.content().readableBytes());
        response1.release();

        assertFalse(channel.finish());
    }

Impact

Integrity/availability of HTTP parsing on that connection, unsafe reuse of the socket.

A client might overload the server by issue frequent RST frames. This can cause a massive amount of load on the remote system and so cause a DDOS attack.

Impact

This is a DDOS attack, any http2 server is affected and so you should update as soon as possible.

Patches

This is patched in version 4.1.100.Final.

Workarounds

A user can limit the amount of RST frames that are accepted per connection over a timeframe manually using either an own Http2FrameListener implementation or an ChannelInboundHandler implementation (depending which http2 API is used).

References

• https://www.cve.org/CVERecord?id=CVE-2023-44487
• https://blog.cloudflare.com/technical-breakdown-http2-rapid-reset-ddos-attack/
• https://cloud.google.com/blog/products/identity-security/google-cloud-mitigated-largest-ddos-attack-peaking-above-398-million-rps/

Red Hat Lightwell has released io.netty:netty-codec-http 4.1.100.Final-rhlw-00001 with backported fixes for CVE-2024-29025, CVE-2025-58056, CVE-2025-67735, CVE-2026-33870, CVE-2026-41417, CVE-2026-42580, CVE-2026-42581, CVE-2026-42584, CVE-2026-42585, CVE-2026-42587, CVE-2026-50020, CVE-2026-55831, CVE-2026-55833, CVE-2026-56745, CVE-2026-56746, CVE-2026-59898, CVE-2026-59899, CVE-2026-59903, and CVE-2026-59921.

CVE-2024-29025: Netty HttpPostRequestDecoder can OOM

CVE-2025-58056: Netty is vulnerable to request smuggling due to incorrect parsing of chunk extensions

CVE-2025-67735: Netty has a CRLF Injection vulnerability in io.netty.handler.codec.http.HttpRequestEncoder

CVE-2026-33870: Netty: HTTP Request Smuggling via Chunked Extension Quoted-String Parsing

CVE-2026-41417: Netty vulnerable to HTTP request smuggling and RTSP request injection via DefaultHttpRequest.setUri()

CVE-2026-42580: Netty: HTTP Request Smuggling due to incorrect chunk size parsing

CVE-2026-42581: Netty: HTTP/1.0 TE+CL Coexistence Bypasses Smuggling Sanitization

CVE-2026-42584: Netty: HttpClientCodec response desynchronization

CVE-2026-42585: Netty: HTTP Request Smuggling due to malformed Transfer-Encoding

CVE-2026-42587: Netty: HttpContentDecompressor maxAllocation bypass via Content-Encoding: br/zstd/snappy enables decompression bomb DoS

CVE-2026-50020: Netty's HttpObjectDecoder skips arbitrary initial control characters when only initial CRLF characters are permitted

CVE-2026-55831: Netty SPDY SETTINGS frame count materializes unbounded settings map

CVE-2026-55833: Netty SPDY zlib header block continues decoded expansion after maxHeaderSize truncation

CVE-2026-56745: Netty SpdyHttpDecoder: ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion

CVE-2026-56746: Netty has a Security Control Bypass via CORS Short-Circuit Failure

CVE-2026-59898: Netty: WebSockets V07/V08 handshaker missing Connection/Upgrade validation

CVE-2026-59899: Netty HttpContentEncoder: Unbounded Per-Connection Queue Growth via HTTP/1.1 Pipelining Leads to Denial of Service

CVE-2026-59903: Netty: Cache Poisoning and Information Disclosure via CORS Vary Header Overwrite

CVE-2026-59921: Netty: CRLF Injection via Multipart Filename in Netty HttpPostRequestEncoder

This patched artifact is a drop-in replacement for io.netty:netty-codec-http 4.1.100.Final from Maven Central.

Root has patched CVE-2026-42584 in the io.netty:netty-codec-http package for Root:Maven. Multiple fixed versions available.

Root has patched GHSA-xpw8-rcwv-8f8p in the io.root.io.netty:netty-codec-http2 package for Root:Maven. Multiple fixed versions available.

Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, HttpClientCodec pairs each inbound response with an outbound request by queue.poll() once per response, including for 1xx. If the client pipelines GET then HEAD and the server sends 103, then 200 with GET body, then 200 for HEAD, the queue pairs HEAD with the first 200. The HEAD rule then skips reading that message’s body, so the GET entity bytes stay on the stream and the following 200 is parsed from the wrong offset. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.

TuxCare rebuilt 47 io.netty packages to address 59 CVEs. Fixed in 4.1.122.Final-tuxcare.2.

TuxCare rebuilt 47 io.netty packages to address 60 CVEs. Fixed in 4.1.119.Final-tuxcare.1.

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