CVE-2026-47244

Netty HTTP/2: Advertised MAXCONCURRENTSTREAMS are not enforced

Resources

https://www.rfc-editor.org/rfc/rfc7540.html#section-6.5.2

DefaultHttp2Connection.DefaultEndpoint initialises maxActiveStreams/maxStreams to Integer.MAX_VALUE, and Http2Settings never inserts SETTINGS_MAX_CONCURRENT_STREAMS by default (Http2Settings.java:305-307 only clamps a user-supplied value). Unless the application explicitly calls initialSettings().maxConcurrentStreams(n), a Netty HTTP/2 server advertises no limit and enforces none locally. Each open stream allocates a DefaultStream object, PropertyMap slots, flow-controller state and IntObjectHashMap entry; with ~2^30 permissible odd stream IDs a single TCP connection can create hundreds of thousands of long-lived stream objects. This is also the precondition for CVE-2023-44487-style Rapid-Reset amplification, where the absence of a low concurrent cap multiplies backend work.

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

CVE-2026-47244 has a CVSS score of 5.3 (Medium). 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 (4.2.15.Final, 4.1.135.Final); upgrading removes the vulnerable code path.

Kodem intelligence

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1. What is CVE-2026-47244? CVE-2026-47244 is a medium-severity uncontrolled resource consumption vulnerability in io.netty:netty-codec-http2 (maven), affecting versions >= 4.2.0.Final, <= 4.2.14.Final. It is fixed in 4.2.15.Final, 4.1.135.Final. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2026-47244? CVE-2026-47244 has a CVSS score of 5.3 (Medium). 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-http2 are affected by CVE-2026-47244? io.netty:netty-codec-http2 (maven) versions >= 4.2.0.Final, <= 4.2.14.Final is affected.
4. Is there a fix for CVE-2026-47244? Yes. CVE-2026-47244 is fixed in 4.2.15.Final, 4.1.135.Final. Upgrade to this version or later.
5. Is CVE-2026-47244 exploitable, and should I be worried? Whether CVE-2026-47244 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-2026-47244 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-2026-47244?
   • Upgrade io.netty:netty-codec-http2 to 4.2.15.Final or later
   • Upgrade io.netty:netty-codec-http2 to 4.1.135.Final or later

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