Netty HTTP/3 QPACK literal unbounded allocation

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-2026-42582: 0.44% estimated exploitation activity in the next 30 days; percentile 38.02 (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 When Netty decodes HTTP/3 headers, it sometimes runs new byte[length] using a length from the wire before checking that many bytes are really there. A small malicious header can claim a huge length (on the order of a gigabyte). Details When decoding header blocks, the non-Huffman branch of io.netty.handler.codec.http3.QpackDecoder#decodeHuffmanEncodedLiteral may execute new byte[length] for a string literal before verifying that length bytes are actually present in the compressed field section. The wire encoding allows a very large length to be expressed in few bytes. There is no check that length <= in.readableBytes() before new byte[length]. PoC The test below constructs a small HTTP/3 HEADERS frame whose QPACK section decodes to a ~1 GiB non-Huffman name length and is used to observe server-side failure; it illustrates how little wire data can target new byte[length]. Impact The server can slow down, stall, or crash under load when many crafted HTTP/3 HEADERS frames…

Published by the source

7 May 2026, 00:19 UTC

Last modified by the source

30 Jun 2026, 22:27 UTC

Source last checked

26 Oct 2026, 16:54 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-2c5c-chwr-9hqw

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# Patch Next advisory brief: CVE-2026-42582

Advisory: Netty HTTP/3 QPACK literal unbounded allocation
IDs: CVE-2026-42582, GHSA-2c5c-chwr-9hqw
Record: https://patchnext.com/advisories/cve-2026-42582 (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 4.2.13.Final. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven io.netty:netty-codec-http3: affected >= 4.2.0.Final, <= 4.2.12.Final; fixed in 4.2.13.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-2c5c-chwr-9hqw (GitHub-reviewed advisory GHSA-2c5c-chwr-9hqw lists affected ranges: Maven io.netty:netty-codec-http3 >=4.2.0.Final <=4.2.12.Final)

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