CVE-2026-59901: Netty [Bzip2Decoder] Infinite Loop Vulnerability

HIGH
Advisory Identifier: GHSA-558v-64gr-wgg4
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CWE-835
Published
Advisory Summary

CVE-2026-59901 is a HIGH [bzip2decoder] infinite loop vulnerability (CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop')) affecting Netty libraries in the Maven ecosystem. The issue involves [bzip2decoder] infinite loop in rle state machine leads to event-loop thread hang. Remediation is available by upgrading affected packages to version 4.2.16.Final, 4.1.136.Final.

CVE-2026-59901 at a Glance

CVE Identifier CVE-2026-59901
GHSA Identifier GHSA-558v-64gr-wgg4
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop')
Affected Product Netty
Package Ecosystem Maven
Published Date
Last Updated

How to Fix CVE-2026-59901

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-compression fixed: 4.2.16.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-codec-compression</artifactId>
    <version>4.2.16.Final</version>
</dependency>
io.netty:netty-codec fixed: 4.1.136.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-codec</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-2026-59901, 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-835: Loop with Unreachable Exit Condition ('Infinite Loop'), where the product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop. 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

The `Bzip2Decoder` handler in Netty's compression codec pipeline is vulnerable to a denial-of-service attack through a malformed bzip2 stream that permanently captures the event-loop thread in an infinite loop. The vulnerability exists in the run-length encoding (RLE) state machine within [`Bzip2BlockDecompressor.read()`]

CVE-2026-59901 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-compression
maven/io.netty/netty-codec-compression
Maven
≥ 4.2.0.Final
< 4.2.16.Final
4.2.16.Final
io.netty:netty-codec
maven/io.netty/netty-codec
Maven
< 4.1.136.Final
4.1.136.Final

References

GitHub Advisory / Wiki ADVISORY
https://github.com/netty/netty/security/advisories/GHSA-558v-64gr-wgg4
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-2026-59901?
CVE-2026-59901 is a security vulnerability in Netty involving [Bzip2Decoder] Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang under CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop').
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-compression, io.netty:netty-codec.
What version fixes CVE-2026-59901?
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-compression affected?
Yes, io.netty:netty-codec-compression is affected in releases prior to 4.2.16.Final. Upgrade your dependency to 4.2.16.Final or later.
Is netty-codec affected?
Yes, io.netty:netty-codec is affected in releases prior to 4.1.136.Final. Upgrade your dependency to 4.1.136.Final or later.
What CWE is associated with CVE-2026-59901?
CVE-2026-59901 is classified under CWE-835: Loop with Unreachable Exit Condition ('Infinite Loop') (The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.).
How can I check Maven dependencies for CVE-2026-59901?
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-558v-64gr-wgg4",
  "modified" : "2026-07-22T21:50:47Z",
  "published" : "2026-07-22T21:50:47Z",
  "aliases" : [ "CVE-2026-59901" ],
  "summary" : "Netty: [Bzip2Decoder] Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang",
  "details" : "The `Bzip2Decoder` handler in Netty's compression codec pipeline is vulnerable to a denial-of-service attack through a malformed bzip2 stream that permanently captures the event-loop thread in an infinite loop. The vulnerability exists in the run-length encoding (RLE) state machine within [`Bzip2BlockDecompressor.read()`]",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-codec-compression"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.2.0.Final"
      }, {
        "fixed" : "4.2.16.Final"
      } ]
    } ]
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-codec"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.1.136.Final"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/security/advisories/GHSA-558v-64gr-wgg4"
  }, {
    "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-835" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-07-22T21:50:47Z",
    "nvd_published_at" : null
  }
}