CVE-2026-56819

Netty: HTTP/2 decompression leaks ByteBuf reference count when the decompressor channel is already closed (Direct memory leak / OOM DoS)

• Vulnerability type: uncontrolled resource consumption / memory leak (CWE-401), leading to
  denial of service. Each crafted DATA frame leaks one (typically direct/off-heap) ByteBuf.
• Who is impacted: any server (or client) that enables HTTP/2 content decompression by installing
  DelegatingDecompressorFrameListener in its HTTP/2 pipeline.
• Attacker requirements: remote, unauthenticated. The attacker only needs to send HTTP/2 DATA
  frames for a stream whose decompressor has been cleaned up (e.g. continue sending DATA after
  END_STREAM). No special server configuration beyond decompression being enabled.
• Result: sustained triggering over a long-lived connection exhausts direct memory and crashes
  the JVM with OutOfMemoryError.

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

CVE-2026-56819 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-2026-56819? CVE-2026-56819 is a high-severity uncontrolled resource consumption vulnerability in io.netty:netty-codec-http2 (maven), affecting versions >= 4.2.0, <= 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-2026-56819? CVE-2026-56819 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-http2 are affected by CVE-2026-56819? io.netty:netty-codec-http2 (maven) versions >= 4.2.0, <= 4.2.15.Final is affected.
4. Is there a fix for CVE-2026-56819? Yes. CVE-2026-56819 is fixed in 4.2.16.Final, 4.1.136.Final. Upgrade to this version or later.
5. Is CVE-2026-56819 exploitable, and should I be worried? Whether CVE-2026-56819 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-2026-56819 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-2026-56819?
   • Upgrade io.netty:netty-codec-http2 to 4.2.16.Final or later
   • Upgrade io.netty:netty-codec-http2 to 4.1.136.Final or later

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