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

Source: https://junglewise.ai/threats/cve-2026-42582-netty-unbounded-memory-allocation-in-http-3-qpack-decoder  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-13. Updated: 2026-06-30  
License: CC BY 4.0 with a link back

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)](https://junglewise.ai/threats/technologies/io-netty-netty-codec-http3), [Netty Codec HTTP/3](https://junglewise.ai/threats/technologies/codec-http-3), [Netty](https://junglewise.ai/threats/technologies/netty), [Netty Project Codec HTTP3](https://junglewise.ai/threats/technologies/codec-http3). Vendors: [Maven](https://junglewise.ai/threats/vendors/maven), [Netty](https://junglewise.ai/threats/vendors/netty), [Netty Project](https://junglewise.ai/threats/vendors/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

  ```sh
  # 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

- [https://api.github.com/users/violetagg](https://api.github.com/users/violetagg)
- [https://github.com/violetagg](https://github.com/violetagg)
- [https://api.github.com/users/violetagg/gists%7B/gist_id%7D](https://api.github.com/users/violetagg/gists%7B/gist_id%7D)
- [https://api.github.com/users/violetagg/repos](https://api.github.com/users/violetagg/repos)
- [https://avatars.githubusercontent.com/u/696661?v=4](https://avatars.githubusercontent.com/u/696661?v=4)
- [https://api.github.com/users/violetagg/events%7B/privacy%7D](https://api.github.com/users/violetagg/events%7B/privacy%7D)

## Related threats

- [Netty HTTP/1 decoder request smuggling](https://junglewise.ai/threats/cve-2026-93562-a-flaw-was-found-in-netty-s-http-1-decoder-incomplete-validation)
- [Netty HTTP/1 to HTTP/2 conversion authority mismatch](https://junglewise.ai/threats/cve-2026-93569-netty-http-1-to-http-2-conversion-authority-mismatch)
- [Netty HTTP request smuggling via control characters in chunk size](https://junglewise.ai/threats/cve-2026-93566-netty-http-request-smuggling-via-control-characters-in-chunk-size)
- [Netty RtspDecoder method-token smuggling in RTSP parsing](https://junglewise.ai/threats/cve-2026-93565-netty-rtspdecoder-method-token-smuggling-in-rtsp-parsing)
- [Netty reference-count leak in HAProxy PROXY-v2 decoder](https://junglewise.ai/threats/cve-2026-93564-netty-reference-count-leak-in-haproxy-proxy-v2-decoder)