How severe is CVE-2026-59899?

No CVSS score has been assigned to CVE-2026-59899 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-59899?

CVE-2026-59899 affects the following packages: io.netty:netty-codec-http (Maven), io.netty:netty-codec-http (Maven). Ecosystems affected: Maven.

How do I fix CVE-2026-59899?

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-2026-59899 is resolved across your whole dependency graph.

How do I detect CVE-2026-59899 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-2026-59899 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2026-59899 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-59899 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-2026-59899?

CVE-2026-59899 has an EPSS (Exploit Prediction Scoring System) score of 0.6%, placing it in the 49th 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-2026-59899?

CVE-2026-59899 is classified as CWE-770 (CWE-770). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-59899 published, and has it been updated?

CVE-2026-59899 was published on July 29, 2026 and was last updated on October 28, 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-2026-59899 — netty-codec-http

CVE-2026-59899 is a CWE-770 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 HttpContentEncoder: Unbounded Per-Connection Queue Growth via HTTP/1.1 Pipelining Leads to Denial of Service

Also known asGHSA-q4f6-jm68-57ww

Published

Jul 29, 2026

Updated

Oct 28, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 27, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
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-2026-59899.

EPSS Exploitation Probability

via FIRST.org ↗

0.6%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs49th percentile — riskier than 49% 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, HttpContentEncoder (the superclass of the production handler HttpContentCompressor) maintains a per-channel ArrayDeque<CharSequence> named acceptEncodingQueue that accumulates attacker-controlled data without any size limit. The queue is filled on the I/O thread for every inbound HTTP request and drained only when the application later writes a non-1xx response. This creates a resource exhaustion vulnerability when an attacker exploits HTTP/1.1 pipelining to flood the connection with requests faster than the application produces responses. 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-2026-59899 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

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 HatImportant

This is an Important vulnerability in Netty's HTTP decoder, which could lead to a denial of service. Red Hat products utilizing `netty-codec-http` are susceptible to memory exhaustion when processing specially crafted, highly compressed HTTP payloads. This allows a remote attacker to trigger excessive memory…

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-2026-59899 (CC BY 4.0)

Product	Fixed in	Advisory
Cryostat 4 on RHEL 9	`cryostat/cryostat-reports-rhel9:4.2.0-14`	RHSA-2026:68333
Red Hat AMQ Broker 7.13.6	`netty-codec-http`	RHSA-2026:66545
Red Hat AMQ Broker 7.14.1	`netty-codec-http`	RHSA-2026:66488
Red Hat Build of Apache Camel 3.33.2.SP3	`io.netty/netty-codec-http:4.1.136.Final-redhat-00001`	RHSA-2026:48118
Red Hat build of Apache Camel 4.18.3 for Spring Boot 3.5.16	`netty-codec-http`	RHSA-2026:54622
Red Hat build of Apicurio Registry 3.3.3	`netty-codec-http`	RHSA-2026:76637
Red Hat build of Keycloak 26.4.14	see advisory	RHSA-2026:50846
Red Hat build of Keycloak 26.6.5	see advisory	RHSA-2026:50848

Frequently Asked Questions

Netty is an asynchronous, event-driven network application framework. Prior to versions 4.1.136.Final and 4.2.16.Final, `HttpContentEncoder` (the superclass of the production handler `HttpContentCompressor`) maintains a per-channel `ArrayDeque<CharSequence>` named `acceptEncodingQueue` that accumulates attacker-controlled data without any size limit. The queue is filled on the I/O thread for every inbound HTTP request and drained only when the application later writes a non-1xx response. This creates a resource exhaustion vulnerability when an attacker exploits HTTP/1.1 pipelining to flood the

O3 Security · Impact-Aware SCA

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