# CVE-2026-56819: Netty memory leak in HTTP/2 content decompression

Source: https://junglewise.ai/threats/cve-2026-56819-netty-memory-leak-in-http-2-content-decompression  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-21. Updated: 2026-07-31  
License: CC BY 4.0 with a link back

CVE-2026-56819 · Severity: high · CVSS 7.5 · Published 2026-07-21

Netty is a popular networking library used by many Java-based web servers and applications to handle data traffic. A flaw in how it handles compressed web traffic (HTTP/2) allows a remote attacker to cause a memory leak by sending specially crafted data packets. Over time, this leak will consume all available system memory, causing the application to crash and resulting in a denial of service for legitimate users.

Technologies: [io.netty:netty-codec-http2 (Maven)](https://junglewise.ai/threats/technologies/io-netty-netty-codec-http2), [Netty Project Netty Codec HTTP2](https://junglewise.ai/threats/technologies/netty-codec-http2). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven), [Netty Project](https://junglewise.ai/threats/vendors/netty-project).

## Quick answers

**Is CVE-2026-56819 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-56819 being exploited in the wild.

**How severe is CVE-2026-56819?** High severity, with a CVSS score of 7.5, published 21 July 2026.

**Which products and versions are affected?** io.netty:netty-codec-http2 (Maven) ECOSYSTEM:introduced=4.2.0,fixed=4.2.16.Final; Netty Project Netty Codec HTTP2 >= 4.2.0, <= 4.2.15.Final.

**Is there a fix for CVE-2026-56819?** Yes. io.netty:netty-codec-http2 (Maven): upgrade to 4.2.16.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-56819 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-56819?** Check whether you run io.netty:netty-codec-http2 (Maven) or Netty Project Netty Codec HTTP2 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- io.netty:netty-codec-http2 (Maven): upgrade to 4.2.16.Final or later

  ```sh
  # set io.netty:netty-codec-http2 to 4.2.16.Final in your pom.xml or build.gradle
  ```


## Technical details

A memory leak exists in DelegatingDecompressorFrameListener.java within the Http2Decompressor.decompress() method. When a DATA frame is received for a stream where the decompressor has already been closed, the code calls data.retain() before writeInbound(), incrementing the reference count. If writeInbound() throws a ClosedChannelException, the error handling path fails to call data.release(), preventing the ByteBuf from ever reaching a zero reference count. An attacker can exploit this by repeatedly sending DATA frames for closed streams over a long-lived HTTP/2 connection to exhaust direct memory. The issue is fixed in Netty versions 4.1.136.Final and 4.2.16.Final.

## Affected products

- Netty netty-codec-http2 >= 4.2.0, <= 4.2.15.Final
- Netty netty-codec-http2 >= 4.1.0.Final, <= 4.1.135.Final

## Identifiers

- CVE-2026-56819
- GHSA-93wv-jw9v-4972

## Timeline

- 2026-07-14: disclosed
- 2026-07-31: advisory

## References

- [https://github.com/netty/netty/security/advisories/GHSA-93wv-jw9v-4972](https://github.com/netty/netty/security/advisories/GHSA-93wv-jw9v-4972)
- [https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b](https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b)
- [https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6](https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6)
- [https://github.com/netty/netty/releases/tag/netty-4.1.136.Final](https://github.com/netty/netty/releases/tag/netty-4.1.136.Final)
- [https://github.com/netty/netty/releases/tag/netty-4.2.16.Final](https://github.com/netty/netty/releases/tag/netty-4.2.16.Final)

## Related threats

- [Netty request smuggling via Host header duplication in HTTP/2 translation](https://junglewise.ai/threats/cve-2026-59900-netty-request-smuggling-via-host-header-duplication-in-http-2)
- [Netty denial of service in HTTP/2 codec via max header size handling](https://junglewise.ai/threats/cve-2026-50560-netty-denial-of-service-in-http-2-codec-via-max-header-size)
- [Netty memory exhaustion in DelegatingDecompressorFrameListener](https://junglewise.ai/threats/cve-2026-48043-netty-memory-exhaustion-in-delegatingdecompressorframelistener)
- [Netty uncontrolled resource consumption in HTTP/2 codec](https://junglewise.ai/threats/cve-2026-47244-netty-uncontrolled-resource-consumption-in-http-2-codec)
- [Netty denial of service via decompression limit bypass](https://junglewise.ai/threats/cve-2026-42587-netty-denial-of-service-via-decompression-limit-bypass)