CVE-2026-42582: Netty unbounded memory allocation in HTTP/3 QPACK decoder

CVE-2026-42582 · Severity: high · CVSS 7.5 · Published 2026-05-13

Netty is a popular networking framework used by many Java applications to handle web traffic. A vulnerability in its HTTP/3 implementation allows a remote attacker to send a specially crafted message that forces the server to allocate massive amounts of memory. This can lead to significant performance slowdowns, service instability, or a complete server crash, potentially disrupting business operations.

Technologies: io.netty:netty-codec-http3 (Maven), Netty Codec HTTP/3, Netty, Netty Project Codec HTTP3. Vendors: Maven, Netty, Netty Project.

Quick answers

Is CVE-2026-42582 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-42582 being exploited in the wild.
How severe is CVE-2026-42582?
High severity, with a CVSS score of 7.5, published 13 May 2026.
Which products and versions are affected?
io.netty:netty-codec-http3 (Maven) <= 4.2.12.Final, >= 4.2.0.Final, <= 4.2.12.Final, ECOSYSTEM:introduced=4.2.0.Final,fixed=4.2.13.Final.
Is there a fix for CVE-2026-42582?
Yes. io.netty:netty-codec-http3 (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-2026-42582 attacked?
It is attacked over the network, in a software library.
Am I affected by CVE-2026-42582?
Check whether you run io.netty:netty-codec-http3 (Maven), Netty Codec HTTP/3, Netty 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-http3 (Maven): upgrade to 4.2.13.Final or later
    # set io.netty:netty-codec-http3 to 4.2.13.Final in your pom.xml or build.gradle

Technical details

A vulnerability exists in the QpackDecoder of Netty's HTTP/3 codec due to improper validation of literal lengths. Specifically, in the non-Huffman branch of decodeHuffmanEncodedLiteral, the decoder performs a byte array allocation based on a length value provided directly from the network wire before verifying if that many bytes are actually available in the buffer. An attacker can exploit this by sending a small, malicious HTTP/3 HEADERS frame that specifies a very large length (e.g., 1GB), leading to excessive memory allocation (CWE-770, CWE-789). This can result in an OutOfMemoryError or IndexOutOfBoundsException, causing a denial of service. The issue is fixed in version 4.2.13.Final.

Affected products

  • Netty netty-codec-http3 >= 4.2.0.Final, <= 4.2.12.Final

Identifiers

  • CVE-2026-42582
  • GHSA-2c5c-chwr-9hqw

Timeline

  • 2026-05-05: disclosed: Vulnerability disclosed by chrisvest
  • 2026-05-07: advisory: GitHub Advisory GHSA-2c5c-chwr-9hqw published
  • 2026-05-13: other: Published to the National Vulnerability Database (NVD)
  • 2026-06-30: other: Advisory last updated

References

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