Is CVE-2026-55831 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-55831 being exploited in the wild.

How severe is CVE-2026-55831?

High severity, with a CVSS score of 7.5, published 21 July 2026.

Which products and versions are affected?

io.netty:netty-codec-http (Maven) ECOSYSTEM:introduced=4.2.0.Final,fixed=4.2.16.Final.

Is there a fix for CVE-2026-55831?

Yes. io.netty:netty-codec-http (Maven): upgrade to 4.2.16.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-55831 attacked?

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

Am I affected by CVE-2026-55831?

Check whether you run io.netty:netty-codec-http (Maven) or Netty Project Codec HTTP 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-2026-55831: Netty resource exhaustion in SPDY SETTINGS decoder

CVE-2026-55831 · Severity: high · CVSS 7.5 · Published 2026-07-21

Netty is a popular networking framework used by many Java-based applications to handle web traffic. A vulnerability in its SPDY protocol implementation allows a remote attacker to crash or slow down a server by sending a specially crafted message. This can lead to a denial-of-service (DoS) condition, making the affected service unavailable to legitimate users.

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

Quick answers

Is CVE-2026-55831 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-55831 being exploited in the wild.
How severe is CVE-2026-55831?: High severity, with a CVSS score of 7.5, published 21 July 2026.
Which products and versions are affected?: io.netty:netty-codec-http (Maven) ECOSYSTEM:introduced=4.2.0.Final,fixed=4.2.16.Final.
Is there a fix for CVE-2026-55831?: Yes. io.netty:netty-codec-http (Maven): upgrade to 4.2.16.Final or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-55831 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-55831?: Check whether you run io.netty:netty-codec-http (Maven) or Netty Project Codec HTTP 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 4.2.16.Final or later

# set io.netty:netty-codec-http to 4.2.16.Final in your pom.xml or build.gradle

Technical details

An uncontrolled resource consumption vulnerability (CWE-400) exists in Netty's SpdyFrameCodec. The SPDY SETTINGS decoder accepts a peer-declared entry count up to the 24-bit frame-length limit without an implementation-level cap. When a crafted frame is received, DefaultSpdySettingsFrame materializes every unique setting ID into a TreeMap. A remote, unauthenticated attacker can send a ~2 MiB frame containing 262,144 entries, causing significant heap growth and CPU consumption due to map insertion work. This can be exploited to trigger a denial-of-service (DoS) via memory exhaustion. The issue is patched in versions 4.1.136.Final and 4.2.16.Final.

Affected products

Netty netty-codec-http >= 4.1.0.Final, <= 4.1.135.Final
Netty netty-codec-http >= 4.2.0.Final, <= 4.2.15.Final

Identifiers

CVE-2026-55831
GHSA-6jqx-86gh-f27w

Timeline

2026-07-14: disclosed: Initial disclosure in Netty repository
2026-07-21: advisory: NVD publication date
2026-07-22: advisory: GitHub Advisory Database publication date

References

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