# CVE-2026-42583: Netty Lz4FrameDecoder resource exhaustion

Source: https://junglewise.ai/threats/cve-2026-42583-netty-lz4framedecoder-resource-exhaustion  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-13. Updated: 2026-05-18  
License: CC BY 4.0 with a link back

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)](https://junglewise.ai/threats/technologies/io-netty-netty-codec), [io.netty:netty-codec-compression (Maven)](https://junglewise.ai/threats/technologies/io-netty-netty-codec-compression). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven), [Netty Project](https://junglewise.ai/threats/vendors/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

  ```sh
  # 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

  ```sh
  # 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

- [https://github.com/netty/netty/security/advisories/GHSA-mj4r-2hfc-f8p6](https://github.com/netty/netty/security/advisories/GHSA-mj4r-2hfc-f8p6)

## Related threats

- [Netty Bzip2Decoder infinite loop denial of service](https://junglewise.ai/threats/cve-2026-59901-netty-bzip2decoder-infinite-loop-denial-of-service)
- [Netty's decoders vulnerable to DoS via zip bomb style attack](https://junglewise.ai/threats/cve-2025-58057-netty-s-decoders-vulnerable-to-dos-via-zip-bomb-style-attack)
- [SnappyFrameDecoder doesn't restrict chunk length any may buffer skippable chunks in an unnecessary way](https://junglewise.ai/threats/cve-2021-37137-snappyframedecoder-doesn-t-restrict-chunk-length-any-may-buffer)
- [Bzip2Decoder doesn't allow setting size restrictions for decompressed data](https://junglewise.ai/threats/cve-2021-37136-bzip2decoder-doesn-t-allow-setting-size-restrictions-for)