How severe is CVE-2026-59898?

No CVSS score has been assigned to CVE-2026-59898 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-59898?

CVE-2026-59898 affects the following packages: io.netty:netty-codec-http (Maven), io.netty:netty-codec-http (Maven). Ecosystems affected: Maven.

How do I fix CVE-2026-59898?

Update io.netty:netty-codec-http to 4.2.16.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-59898 is resolved across your whole dependency graph.

How do I detect CVE-2026-59898 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-codec-http, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-59898 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-59898 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-59898 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-59898?

CVE-2026-59898 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 37th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-59898?

CVE-2026-59898 is classified as CWE-444 (CWE-444). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-59898 published, and has it been updated?

CVE-2026-59898 was published on July 29, 2026 and was last updated on October 21, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕ Maven

Not in CISA KEV

CVE-2026-59898 — netty-codec-http

CVE-2026-59898 is a CWE-444 vulnerability in io.netty:netty-codec-http. A fix is available for io.netty:netty-codec-http — see the affected versions and patch details below.

Netty: WebSockets V07/V08 handshaker missing Connection/Upgrade validation

Also known asGHSA-4mp9-239f-g9hg

Published

Jul 29, 2026

Updated

Oct 21, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 21, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-59898.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs37th percentile — riskier than 37% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

2 pkgs affected

☕io.netty:netty-codec-http☕io.netty:netty-codec-http

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.

Description

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, ab attacker can force WebSocket upgrade via the lax V07 (or V08) handshaker by sending Sec-WebSocket-Version: 7 and omitting Connection: Upgrade / Upgrade: websocket headers, completing a protocol switch that a proxy would not recognize as an Upgrade request and enabling HTTP request smuggling / protocol-confusion attacks. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`io.netty:netty-codec-http`	≥ 4.2.0.Final&&< 4.2.16.Final	4.2.16.Final`io.netty:netty-codec-http:4.2.16.Final`
☕Maven	`io.netty:netty-codec-http`	all versions	4.1.136.Final`io.netty:netty-codec-http:4.1.136.Final`

Affected Products

1 product · 2 configurations

Application

nettynetty

≥ 4.2.0 && < 4.2.16

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.netty:netty-codec-http, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.netty:netty-codec-http to 4.2.16.Final or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-59898 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

This Moderate flaw in Netty's WebSocket handshaker, specifically within `netty-codec-http`, could allow an attacker to bypass security checks or force unexpected protocol versions during the WebSocket upgrade process. This issue primarily impacts Red Hat products that leverage Netty for WebSocket communication,…

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.

Source: Red Hat security advisory for CVE-2026-59898 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat build of Quarkus 3.27.4.SP3	`io.netty/netty-codec-http:4.1.136.Final-redhat-00001`	RHSA-2026:47189
Red Hat build of Quarkus 3.33.2.SP3	`io.netty/netty-codec-http:4.1.136.Final-redhat-00001`	RHSA-2026:47172

Frequently Asked Questions

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, ab attacker can force WebSocket upgrade via the lax V07 (or V08) handshaker by sending `Sec-WebSocket-Version: 7` and omitting `Connection: Upgrade` / `Upgrade: websocket` headers, completing a protocol switch that a proxy would not recognize as an Upgrade request and enabling HTTP request smuggling / protocol-confusion attacks. This issue has been fixed in versions 4.1.136.Final and 4.2.16.Final.

O3 Security · Impact-Aware SCA

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