CVE-2026-59899: Netty Denial of Service Vulnerability

MODERATE
Advisory Identifier: GHSA-q4f6-jm68-57ww
Share
CWE-770
Published
Advisory Summary

CVE-2026-59899 is a MODERATE denial of service vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting Netty libraries in the Maven ecosystem. The issue involves [httpcontentencoder] unbounded per-connection queue growth via http/1.1 pipelining leads to denial of service. Remediation is available by upgrading affected packages to version 4.2.16.Final, 4.1.136.Final.

CVE-2026-59899 at a Glance

CVE Identifier CVE-2026-59899
GHSA Identifier GHSA-q4f6-jm68-57ww
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-770: Allocation of Resources Without Limits or Throttling
Affected Product Netty
Package Ecosystem Maven
Published Date
Last Updated

How to Fix CVE-2026-59899

To remediate this vulnerability, upgrade all affected Netty dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

io.netty:netty-codec-http fixed: 4.2.16.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-codec-http</artifactId>
    <version>4.2.16.Final</version>
</dependency>
io.netty:netty-codec-http fixed: 4.1.136.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-codec-http</artifactId>
    <version>4.1.136.Final</version>
</dependency>
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

mvn dependency:tree -Dincludes=io.netty

How to Check if You Are Affected

To determine whether your Java application is affected by CVE-2026-59899, inspect your build dependencies using the Maven Dependency Plugin:

mvn dependency:tree -Dincludes=io.netty

Analyze the terminal output to locate any version of Netty in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.2.16.Final), your application is affected.

Note: The mvn dependency:tree -Dincludes=io.netty command inspects the resolved dependency graph declared in your project's POM files; it does not perform automated security scanning or inspect runtime dynamic classpaths. Always verify runtime container classpaths and shaded JARs.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-770: Allocation of Resources Without Limits or Throttling, where the product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. In Netty, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Impact `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.

CVE-2026-59899 Affected Netty Versions

2 component(s)
Fixed Versions:
4.2.16.Final4.1.136.Final
Product / Package Ecosystem Affected Versions Fixed Version
io.netty:netty-codec-http
maven/io.netty/netty-codec-http
Maven
≥ 4.2.0.Final
< 4.2.16.Final
4.2.16.Final
io.netty:netty-codec-http
maven/io.netty/netty-codec-http
Maven
< 4.1.136.Final
4.1.136.Final

References

GitHub Advisory / Wiki ADVISORY
https://github.com/netty/netty/security/advisories/GHSA-q4f6-jm68-57ww
Netty Source Repository REPOSITORY
https://github.com/netty/netty
Netty Release RELEASE
https://github.com/netty/netty/releases/tag/netty-4.1.136.Final
Netty Release RELEASE
https://github.com/netty/netty/releases/tag/netty-4.2.16.Final

Frequently Asked Questions

What is CVE-2026-59899?
CVE-2026-59899 is a security vulnerability in Netty involving [HttpContentEncoder] Unbounded Per-Connection Queue Growth via HTTP/1.1 Pipelining Leads to Denial of Service under CWE-770: Allocation of Resources Without Limits or Throttling.
Which Netty versions are affected?
Affected versions include releases prior to 4.2.16.Final, 4.1.136.Final across affected packages: io.netty:netty-codec-http.
What version fixes CVE-2026-59899?
Upgrading to 4.2.16.Final, 4.1.136.Final (or the latest patched release for your respective branch) resolves the vulnerability.
Is netty-codec-http affected?
Yes, io.netty:netty-codec-http is affected in releases prior to 4.2.16.Final, 4.1.136.Final. Upgrade your dependency to 4.2.16.Final, 4.1.136.Final or later.
What CWE is associated with CVE-2026-59899?
CVE-2026-59899 is classified under CWE-770: Allocation of Resources Without Limits or Throttling (The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.).
How can I check Maven dependencies for CVE-2026-59899?
Run the dependency tree command: 'mvn dependency:tree -Dincludes=io.netty'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-q4f6-jm68-57ww",
  "modified" : "2026-07-22T21:49:13Z",
  "published" : "2026-07-22T21:49:13Z",
  "aliases" : [ "CVE-2026-59899" ],
  "summary" : "Netty: [HttpContentEncoder] Unbounded Per-Connection Queue Growth via HTTP/1.1 Pipelining Leads to Denial of Service",
  "details" : "### Impact\n`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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-codec-http"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.2.0.Final"
      }, {
        "fixed" : "4.2.16.Final"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.2.15.Final"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-codec-http"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.1.136.Final"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/security/advisories/GHSA-q4f6-jm68-57ww"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/netty/netty"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/releases/tag/netty-4.1.136.Final"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/releases/tag/netty-4.2.16.Final"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-22T21:49:13Z",
    "nvd_published_at" : null
  }
}