CVE-2026-89044: Netty versions 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through 4.2.17.Final fail to properly vali

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MEDIUM 6.5REMOTEUPGRADE

CVE-2026-89044 is a medium-severity flaw (CVSS 6.5) affecting netty. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Netty versions 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through 4.2.17.Final fail to properly validate the final transfer coding in the Transfer-Encoding header, allowing attackers to smuggle requests by using malformed encoding declarations. Attackers can split Transfer-Encoding headers across multiple lines or use values like 'chunked, xchunked' to bypass validation and decode messages as chunked when the final coding is not chunked

Why this priority

Public exploit reference
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 79%)
CISA exploited list	No
Weakness	CWE-444
Published	2026-09-10
Last modified	2026-09-18

Publisher (CNA): VulnCheck · Vendor: netty

Last updated 2026-09-18 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-10 18:18 UTCPublished CVE record published
2026-09-18 18:17 UTCUpdated Record last modified

netty netty UPGRADE

Affected: >= 4.1.133 and < 4.1.138 · >= 4.2.13 and < 4.2.18

Fixed in: 4.1.138, 4.2.18

Safe to downgrade to: a release before 4.1.133

1. Check installed version

apt-cache policy netty || rpm -q netty || netty --version

2. UPGRADE to 4.1.138 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade netty

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade netty

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 4.1.133 (Debian / Ubuntu)

apt-cache madison netty sudo apt install netty=<VERSION_BEFORE_4.1.133> sudo apt-mark hold netty

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list netty sudo dnf downgrade netty-<VERSION_BEFORE_4.1.133> sudo dnf versionlock add netty

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-89044?

netty: upgrade to 4.1.138, 4.2.18. Exact commands for each OS are on this page.

Is CVE-2026-89044 being exploited?

CVE-2026-89044 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-89044 affect?

CVE-2026-89044 affects netty. Severity is medium (CVSS 6.5). Netty versions 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through 4.2.17.Final fail to properly validate the final transfer coding in the Transfer-Encoding header, allowing attackers to smuggle requests by using malformed encoding

How urgent is CVE-2026-89044?

Priority 38/100. Public exploit reference; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-42587 HIGH 7.5 UPGRADE Netty is an asynchronous, event-driven network application framework
CVE-2026-42584 HIGH 7.3 UPGRADE Netty is an asynchronous, event-driven network application framework
CVE-2026-42583 HIGH 7.5 UPGRADE Netty is an asynchronous, event-driven network application framework
CVE-2026-42580 MEDIUM 6.5 UPGRADE Netty is an asynchronous, event-driven network application framework
CVE-2026-42585 MEDIUM 6.5 UPGRADE Netty is an asynchronous, event-driven network application framework

References

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