CVE-2026-59898: Netty WebSockets V07/V08 Handshaker Missing Connection/Upgrade Vulnerability

MODERATE
Advisory Identifier: GHSA-4mp9-239f-g9hg
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CWE-444
Published
Advisory Summary

CVE-2026-59898 is a MODERATE websockets v07/v08 handshaker missing connection/upgrade vulnerability (CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')) affecting Netty libraries in the Maven ecosystem. The issue involves websockets v07/v08 handshaker missing connection/upgrade validation. Remediation is available by upgrading affected packages to version 4.2.16.Final, 4.1.136.Final.

CVE-2026-59898 at a Glance

CVE Identifier CVE-2026-59898
GHSA Identifier GHSA-4mp9-239f-g9hg
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Affected Product Netty
Package Ecosystem Maven
Published Date
Last Updated

How to Fix CVE-2026-59898

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-2026-59898, 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-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling'), where the product acts as an intermediary http agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed http requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination. 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

## Summary An 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.

CVE-2026-59898 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-4mp9-239f-g9hg
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-2026-59898?
CVE-2026-59898 is a security vulnerability in Netty involving WebSockets V07/V08 handshaker missing Connection/Upgrade validation under CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling').
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-2026-59898?
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-2026-59898?
CVE-2026-59898 is classified under CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') (The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.).
How can I check Maven dependencies for CVE-2026-59898?
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-4mp9-239f-g9hg",
  "modified" : "2026-07-22T21:48:59Z",
  "published" : "2026-07-22T21:48:59Z",
  "aliases" : [ "CVE-2026-59898" ],
  "summary" : "Netty: WebSockets V07/V08 handshaker missing Connection/Upgrade validation",
  "details" : "## Summary\nAn 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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"
  } ],
  "affected" : [ {
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      "name" : "io.netty:netty-codec-http"
    },
    "ranges" : [ {
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      }, {
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      } ]
    } ],
    "database_specific" : {
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    }
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      } ]
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  } ],
  "references" : [ {
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  }, {
    "type" : "PACKAGE",
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  }, {
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    "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-444" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-22T21:48:59Z",
    "nvd_published_at" : null
  }
}