CVE-2026-42584

Netty has HttpClientCodec response desynchronization

    @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());
    }

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

CVE-2026-42584 has a CVSS score of 7.3 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.2.13.Final, 4.1.133.Final); upgrading removes the vulnerable code path.

Kodem intelligence

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1. What is CVE-2026-42584? CVE-2026-42584 is a high-severity security vulnerability in io.netty:netty-codec-http (maven), affecting versions >= 4.2.0.Alpha1, <= 4.2.12.Final. It is fixed in 4.2.13.Final, 4.1.133.Final.
2. How severe is CVE-2026-42584? CVE-2026-42584 has a CVSS score of 7.3 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of io.netty:netty-codec-http are affected by CVE-2026-42584? io.netty:netty-codec-http (maven) versions >= 4.2.0.Alpha1, <= 4.2.12.Final is affected.
4. Is there a fix for CVE-2026-42584? Yes. CVE-2026-42584 is fixed in 4.2.13.Final, 4.1.133.Final. Upgrade to this version or later.
5. Is CVE-2026-42584 exploitable, and should I be worried? Whether CVE-2026-42584 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-42584 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-42584?
   • Upgrade io.netty:netty-codec-http to 4.2.13.Final or later
   • Upgrade io.netty:netty-codec-http to 4.1.133.Final or later

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