CVE-2026-42587: Netty denial of service via decompression limit bypass

CVE-2026-42587 · Severity: high · CVSS 7.5 · Published 2026-05-13

Netty is a widely used networking framework that helps Java applications handle web traffic. A security flaw allows attackers to bypass built-in protections designed to prevent 'decompression bombs'—maliciously crafted files that expand to a massive size when opened. By sending these files using specific compression formats like Brotli or Zstd, an attacker can crash the server by exhausting its memory, leading to a total service outage.

Technologies: io.netty:netty-codec-http (Maven), io.netty:netty-codec-http2 (Maven), Netty Project Codec HTTP. Vendors: Maven, Netty Project.

Quick answers

Is CVE-2026-42587 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-42587 being exploited in the wild.
How severe is CVE-2026-42587?
High severity, with a CVSS score of 7.5, published 13 May 2026.
Which products and versions are affected?
io.netty:netty-codec-http (Maven) ECOSYSTEM:introduced=4.2.0.Alpha1,fixed=4.2.13.Final; io.netty:netty-codec-http2 (Maven) ECOSYSTEM:introduced=4.2.0.Alpha1,fixed=4.2.13.Final.
Is there a fix for CVE-2026-42587?
Yes. io.netty:netty-codec-http (Maven): upgrade to 4.2.13.Final or later; io.netty:netty-codec-http2 (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-2026-42587 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-42587?
Check whether you run io.netty:netty-codec-http (Maven), io.netty:netty-codec-http2 (Maven), Netty Project Codec HTTP 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-http (Maven): upgrade to 4.2.13.Final or later
    # set io.netty:netty-codec-http to 4.2.13.Final in your pom.xml or build.gradle
  • io.netty:netty-codec-http2 (Maven): upgrade to 4.2.13.Final or later
    # set io.netty:netty-codec-http2 to 4.2.13.Final in your pom.xml or build.gradle

Technical details

A resource consumption vulnerability exists in Netty's HttpContentDecompressor and DelegatingDecompressorFrameListener. While the framework provides a 'maxAllocation' parameter to limit decompression buffer sizes, this limit is only enforced for gzip and deflate encodings. When an attacker specifies 'br' (Brotli), 'zstd', or 'snappy' in the Content-Encoding header, the limit is ignored, leading to unbounded memory allocation. This allows a remote, unauthenticated attacker to trigger an OutOfMemoryError (OOM) and crash the application by sending a small, highly compressed payload. The issue is resolved in versions 4.2.13.Final and 4.1.133.Final by properly passing and enforcing the allocation limits across all supported decoders.

Affected products

  • Netty netty-codec-http <= 4.2.12.Final, <= 4.1.132.Final
  • Netty netty-codec-http2 <= 4.2.12.Final, <= 4.1.132.Final

Identifiers

  • CVE-2026-42587
  • GHSA-f6hv-jmp6-3vwv

Timeline

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

References

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