Is CVE-2026-33871 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-33871 being exploited in the wild.

How severe is CVE-2026-33871?

High severity, with a CVSS score of 7.5, published 27 March 2026.

Which products and versions are affected?

io.netty:netty-codec-http2 (Maven) ECOSYSTEM:introduced=0,fixed=4.1.132.Final.

Is there a fix for CVE-2026-33871?

Yes. io.netty:netty-codec-http2 (Maven): upgrade to 4.1.132.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-33871 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-33871?

Check whether you run io.netty:netty-codec-http2 (Maven) 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.

CVE-2026-33871: Netty Denial of Service via HTTP/2 CONTINUATION frame flood

CVE-2026-33871 · Severity: high · CVSS 7.5 · Published 2026-03-27

Netty is a widely used networking framework that helps Java applications communicate over the internet. A vulnerability in its handling of HTTP/2 traffic allows a remote attacker to overwhelm a server's processor (CPU) by sending a flood of specific empty data packets. This can cause the server to become completely unresponsive, leading to a service outage for legitimate customers and users.

Technologies: io.netty:netty-codec-http2 (Maven). Vendors: Maven.

Quick answers

Is CVE-2026-33871 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-33871 being exploited in the wild.
How severe is CVE-2026-33871?: High severity, with a CVSS score of 7.5, published 27 March 2026.
Which products and versions are affected?: io.netty:netty-codec-http2 (Maven) ECOSYSTEM:introduced=0,fixed=4.1.132.Final.
Is there a fix for CVE-2026-33871?: Yes. io.netty:netty-codec-http2 (Maven): upgrade to 4.1.132.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-33871 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-33871?: Check whether you run io.netty:netty-codec-http2 (Maven) 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-http2 (Maven): upgrade to 4.1.132.Final or later

# set io.netty:netty-codec-http2 to 4.1.132.Final in your pom.xml or build.gradle

Technical details

The vulnerability exists in Netty's DefaultHttp2FrameReader component. When an HTTP/2 HEADERS frame is received without the END_HEADERS flag, the server expects CONTINUATION frames; however, the verifyContinuationFrame() method fails to enforce a limit on the number of these frames. Furthermore, the existing maxHeaderListSize mitigation is bypassed when an attacker sends zero-byte payloads, as the size-based check is never triggered. An unauthenticated remote attacker can exploit this by sending a continuous stream of zero-byte CONTINUATION frames, exhausting CPU resources on the handling thread. The issue is fixed in versions 4.1.132.Final and 4.2.10.Final.

Affected products

Netty Project Netty < 4.1.132.Final, < 4.2.10.Final
Red Hat Red Hat JBoss Enterprise Application Platform 8.1
Red Hat Red Hat OpenShift Dev Spaces 3.27.1

Identifiers

CVE-2026-33871
GHSA-w9fj-cfpg-grvv

Timeline

2026-03-24: advisory: GitHub Security Advisory published by Netty project
2026-03-27: disclosed: NVD publication date
2026-04-23: patched: Red Hat released security updates for affected products

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.