Netty: Memory Exhaustion via HTTP/3 Reserved Frame Types

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-56816: 0.64% estimated exploitation activity in the next 30 days; percentile 50.92 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Netty's Http3FrameCodec buffers incoming data for HTTP/3 reserved frame types up to the specified payload length without any limits. The payload length is read directly from the wire and trusted without validation. A bad actor can send a reserved frame with a payload length of up to Integer.MAXVALUE, causing the server to buffer the data in memory. This leads to an OOM and a gradual Denial of Service due to memory exhaustion as multiple streams are opened. Details io.netty.handler.codec.http3.Http3FrameCodec#decodeFrame handles reserved frame types as follows: The payLoadLength is read directly from the wire and trusted implicitly. Since payLoadLength can be up to Integer.MAXVALUE and there is no maximum payload length enforcement for reserved frames, the decoder will accumulate bytes in memory until the wire-provided length is reached. This allows a bad actor to exhaust server memory by opening multiple QUIC streams and sending reserved frames with large payload lengths,…

Published by the source

22 Jul 2026, 21:42 UTC

Last modified by the source

22 Jul 2026, 21:42 UTC

Source last checked

26 Oct 2026, 16:54 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-hpcc-26xq-25fv

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# Patch Next advisory brief: CVE-2026-56816

Advisory: Netty: Memory Exhaustion via HTTP/3 Reserved Frame Types
IDs: CVE-2026-56816, GHSA-hpcc-26xq-25fv
Record: https://patchnext.com/advisories/cve-2026-56816 (revision 1, source checked 26 Oct 2026, 16:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: io.netty:netty-codec-http3 4.2.16.Final. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven io.netty:netty-codec-http3: affected < 4.2.16.Final; fixed in 4.2.16.Final

## Suggested inspection (read-only)
- Maven io.netty:netty-codec-http3: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on io.netty:netty-codec-http3.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-hpcc-26xq-25fv (GitHub-reviewed advisory GHSA-hpcc-26xq-25fv lists affected ranges: Maven io.netty:netty-codec-http3 >=0 <4.2.16.Final)

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