# CVE-2026-56816: Netty memory exhaustion in Http3FrameCodec

Source: https://junglewise.ai/threats/cve-2026-56816-netty-memory-exhaustion-in-http3framecodec  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-21. Updated: 2026-07-22  
License: CC BY 4.0 with a link back

CVE-2026-56816 · Severity: high · CVSS 7.5 · Published 2026-07-21

Netty, a popular networking framework for Java applications, contains a vulnerability in its HTTP/3 implementation. An attacker can send specially crafted network traffic that forces the server to consume excessive amounts of memory. This can lead to a system crash or service outage, preventing legitimate users from accessing the application.

Technologies: [io.netty:netty-codec-http3 (Maven)](https://junglewise.ai/threats/technologies/io-netty-netty-codec-http3), [Netty Codec HTTP/3](https://junglewise.ai/threats/technologies/codec-http-3). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven), [Netty](https://junglewise.ai/threats/vendors/netty).

## Quick answers

**Is CVE-2026-56816 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-56816 being exploited in the wild.

**How severe is CVE-2026-56816?** High severity, with a CVSS score of 7.5, published 21 July 2026.

**Which products and versions are affected?** io.netty:netty-codec-http3 (Maven) < 4.2.16.Final, ECOSYSTEM:introduced=0,fixed=4.2.16.Final.

**Is there a fix for CVE-2026-56816?** Yes. io.netty:netty-codec-http3 (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-2026-56816 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-56816?** Check whether you run io.netty:netty-codec-http3 (Maven) or Netty Codec HTTP/3 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-http3 (Maven): upgrade to 4.2.16.Final or later

  ```sh
  # set io.netty:netty-codec-http3 to 4.2.16.Final in your pom.xml or build.gradle
  ```


## Technical details

An uncontrolled resource consumption vulnerability exists in Netty's Http3FrameCodec. The decodeFrame method handles HTTP/3 reserved frame types by reading the payload length directly from the wire and trusting it without validation. An unauthenticated remote attacker can send a reserved frame with a payload length up to Integer.MAX_VALUE across multiple QUIC streams. This causes the server to buffer data in memory until the specified length is reached, leading to OutOfMemory (OOM) errors and a Denial of Service (DoS). The issue is fixed in version 4.2.16.Final.

## Affected products

- Netty netty-codec-http3 < 4.2.16.Final

## Identifiers

- CVE-2026-56816
- GHSA-hpcc-26xq-25fv

## Timeline

- 2026-07-14: patched: Fix released in version 4.2.16.Final
- 2026-07-21: advisory: NVD publication date
- 2026-07-22: disclosed: GitHub Advisory published

## References

- [https://api.github.com/users/violetagg](https://api.github.com/users/violetagg)
- [https://github.com/violetagg](https://github.com/violetagg)
- [https://api.github.com/users/violetagg/gists%7B/gist_id%7D](https://api.github.com/users/violetagg/gists%7B/gist_id%7D)
- [https://api.github.com/users/violetagg/repos](https://api.github.com/users/violetagg/repos)
- [https://avatars.githubusercontent.com/u/696661?v=4](https://avatars.githubusercontent.com/u/696661?v=4)
- [https://api.github.com/users/violetagg/events%7B/privacy%7D](https://api.github.com/users/violetagg/events%7B/privacy%7D)

## Related threats

- [Netty memory exhaustion in HTTP/3 QPACK decoder](https://junglewise.ai/threats/cve-2026-48748-netty-memory-exhaustion-in-http-3-qpack-decoder)
- [Netty memory exhaustion in Http3ConnectionHandler](https://junglewise.ai/threats/cve-2026-44892-netty-memory-exhaustion-in-http3connectionhandler)
- [Netty unbounded memory allocation in HTTP/3 QPACK decoder](https://junglewise.ai/threats/cve-2026-42582-netty-unbounded-memory-allocation-in-http-3-qpack-decoder)