Netty Lz4FrameDecoder is vulnerable to resource exhaustion

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-2026-42583: 0.46% estimated exploitation activity in the next 30 days; percentile 40.00 (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 Lz4FrameDecoder allocates a ByteBuf of size decompressedLength (up to 32 MB per block) before LZ4 runs. A peer only needs a 21-byte header plus compressedLength payload bytes - 22 bytes if compressedLength == 1 - to force that allocation. Details io.netty.handler.codec.compression.Lz4FrameDecoder#decode Header fields are trusted for sizing. On the compressed path, after readableBytes = compressedLength, the decoder does ctx.alloc().buffer(decompressedLength, decompressedLength) then decompresses. PoC The test below demonstrates how an attacker sending 22 bytes will force the server to allocate 32MB Impact Untrusted senders without per-channel / aggregate limits can stress memory with many small requests.

Published by the source

7 May 2026, 00:20 UTC

Last modified by the source

14 May 2026, 20:41 UTC

Source last checked

26 Oct 2026, 16:45 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-mj4r-2hfc-f8p6

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# Patch Next advisory brief: CVE-2026-42583

Advisory: Netty Lz4FrameDecoder is vulnerable to resource exhaustion
IDs: CVE-2026-42583, GHSA-mj4r-2hfc-f8p6
Record: https://patchnext.com/advisories/cve-2026-42583 (revision 1, source checked 26 Oct 2026, 16:45 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-compression 4.2.13.Final; io.netty:netty-codec 4.1.133.Final. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven io.netty:netty-codec-compression: affected <= 4.2.12.Final; fixed in 4.2.13.Final
- Maven io.netty:netty-codec: affected <= 4.1.132.Final; fixed in 4.1.133.Final

## Suggested inspection (read-only)
- Maven io.netty:netty-codec-compression: check the installed version with your package manager.
- Maven io.netty:netty-codec: 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-compression, io.netty:netty-codec.
- 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-mj4r-2hfc-f8p6 (GitHub-reviewed advisory GHSA-mj4r-2hfc-f8p6 lists affected ranges: Maven io.netty:netty-codec-compression >=0 =0 <=4.1.132.Final)

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