CVE-2026-42583: Netty Lz4FrameDecoder resource exhaustion

CVE-2026-42583 · Severity: high · CVSS 7.5 · Published 2026-05-13

Netty is a widely used networking framework that helps Java applications communicate over the internet. A flaw in how it handles compressed data allows a remote attacker to force the application to allocate large amounts of memory using very small requests. This can lead to a denial-of-service (DoS) condition where the application crashes or becomes unresponsive due to memory exhaustion.

Technologies: io.netty:netty-codec (Maven), io.netty:netty-codec-compression (Maven). Vendors: Maven, Netty Project.

Quick answers

Is CVE-2026-42583 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-42583 being exploited in the wild.
How severe is CVE-2026-42583?
High severity, with a CVSS score of 7.5, published 13 May 2026.
Which products and versions are affected?
io.netty:netty-codec (Maven) <= 4.1.132.Final, ECOSYSTEM:introduced=0,fixed=4.1.133.Final; io.netty:netty-codec-compression (Maven) <= 4.2.12.Final, ECOSYSTEM:introduced=0,fixed=4.2.13.Final; Netty Project Codec <= 4.1.132.Final.
Is there a fix for CVE-2026-42583?
Yes. io.netty:netty-codec (Maven): upgrade to 4.1.133.Final or later; io.netty:netty-codec-compression (Maven): upgrade to 4.2.13.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-42583 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-42583?
Check whether you run io.netty:netty-codec (Maven), io.netty:netty-codec-compression (Maven), Netty Project Codec or one of the others listed 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 (Maven): upgrade to 4.1.133.Final or later
    # set io.netty:netty-codec to 4.1.133.Final in your pom.xml or build.gradle
  • io.netty:netty-codec-compression (Maven): upgrade to 4.2.13.Final or later
    # set io.netty:netty-codec-compression to 4.2.13.Final in your pom.xml or build.gradle

Technical details

The Lz4FrameDecoder in Netty fails to properly validate the 'decompressedLength' field in LZ4 frame headers before allocating memory. An attacker can send a specially crafted 21-byte header that specifies a large decompression size (up to 32 MB), forcing the decoder to allocate a ByteBuf of that size before the actual decompression occurs. By sending multiple such small requests, a remote, unauthenticated attacker can exhaust the heap memory of the application. This vulnerability affects the io.netty:netty-codec and io.netty:netty-codec-compression packages and is fixed in versions 4.1.133.Final and 4.2.13.Final.

Affected products

  • Netty netty-codec <= 4.1.132.Final
  • Netty netty-codec-compression <= 4.2.12.Final

Identifiers

  • CVE-2026-42583
  • GHSA-mj4r-2hfc-f8p6

Timeline

  • 2026-05-05: advisory: GitHub Security Advisory published
  • 2026-05-13: disclosed: CVE published to NVD

References

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