CVE-2026-45673: Netty Remote Code Execution Vulnerability

MODERATE
Advisory Identifier: GHSA-xmv7-r254-6q78
Share
CVSS 6.8
CWE-330 CWE-340
Published
Advisory Summary

CVE-2026-45673 is a MODERATE (CVSS 6.8) remote code execution vulnerability (CWE-330: Use of Insufficiently Random Values) affecting Netty libraries in the Maven ecosystem. The issue involves dns cache poisoning due to predictable prng and default static source port. Remediation is available by upgrading affected packages to version 4.2.15.Final, 4.1.135.Final.

CVE-2026-45673 at a Glance

CVE Identifier CVE-2026-45673
GHSA Identifier GHSA-xmv7-r254-6q78
Severity MODERATE
CVSS v3.1 Base Score 6.8
CWE Classification CWE-330: Use of Insufficiently Random Values
Affected Product Netty
Package Ecosystem Maven
Published Date
Last Updated

Security Impact

CVSS: 6.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N).

Attack Vector Network (AV:N)
Attack Complexity High (AC:H)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Changed (S:C)
Confidentiality None (C:N)
Integrity High (I:H)
Availability None (A:N)

How to Fix CVE-2026-45673

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-resolver-dns fixed: 4.2.15.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-resolver-dns</artifactId>
    <version>4.2.15.Final</version>
</dependency>
io.netty:netty-resolver-dns fixed: 4.1.135.Final 
<dependency>
    <groupId>io.netty</groupId>
    <artifactId>netty-resolver-dns</artifactId>
    <version>4.1.135.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-2026-45673, 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 4.2.15.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-330: Use of Insufficiently Random Values, where the product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers. 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 Netty's DNS resolver uses a predictable PRNG for generating DNS transaction IDs and defaults to a static UDP source port. This combination reduces the entropy of DNS queries, enabling DNS Cache Poisoning (Kaminsky attack). ### Details Two factors contribute to this vulnerability in io.netty.resolver.dns: - Predictable Query IDs: `DnsQueryIdSpace` manages 16-bit transaction IDs in buckets of 16,384 IDs. It initializes only the first bucket. When an ID is returned, it is pushed back into the bucket at a random index generated by java.util.concurrent.ThreadLocalRandom: ```java Random random = ThreadLocalRandom.current(); int insertionPosition = random.nextInt(count + 1); ``` Because ThreadLocalRandom is a predictable LCG and the resolver operates within a single bucket, the sequence of IDs is predictable once the PRNG state is mathematically recovered. - Default Static Source Port: `DnsNameResolverBuilder` defaults to a `channelStrategy` of `ChannelPerResolver`. This binds the DatagramChannel once, resulting in a static source port for all subsequent queries. Combined, a static source port and predictable transaction IDs reduces the entropy required to secure DNS resolution against spoofing. ### Impact DNS Cache Poisoning. Downstream applications using the default Netty DNS resolver may connect to malicious IPs, leading to traffic interception or MitM attacks.

CVE-2026-45673 Affected Netty Versions

2 component(s)
Fixed Versions:
4.2.15.Final4.1.135.Final
Product / Package Ecosystem Affected Versions Fixed Version
io.netty:netty-resolver-dns
maven/io.netty/netty-resolver-dns
Maven
≥ 4.2.0.Final
< 4.2.15.Final
4.2.15.Final
io.netty:netty-resolver-dns
maven/io.netty/netty-resolver-dns
Maven
< 4.1.135.Final
4.1.135.Final

References

GitHub Advisory / Wiki ADVISORY
https://github.com/netty/netty/security/advisories/GHSA-xmv7-r254-6q78
NVD — CVE-2026-45673 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-45673
Netty Source Repository REPOSITORY
https://github.com/netty/netty
Netty Release RELEASE
https://github.com/netty/netty/releases/tag/netty-4.1.135.Final
Netty Release RELEASE
https://github.com/netty/netty/releases/tag/netty-4.2.15.Final

Frequently Asked Questions

What is CVE-2026-45673?
CVE-2026-45673 is a security vulnerability in Netty involving DNS Cache Poisoning due to Predictable PRNG and Default Static Source Port under CWE-330: Use of Insufficiently Random Values.
Which Netty versions are affected?
Affected versions include releases prior to 4.2.15.Final, 4.1.135.Final across affected packages: io.netty:netty-resolver-dns.
What version fixes CVE-2026-45673?
Upgrading to 4.2.15.Final, 4.1.135.Final (or the latest patched release for your respective branch) resolves the vulnerability.
Is netty-resolver-dns affected?
Yes, io.netty:netty-resolver-dns is affected in releases prior to 4.2.15.Final, 4.1.135.Final. Upgrade your dependency to 4.2.15.Final, 4.1.135.Final or later.
What is the CVSS score of CVE-2026-45673?
CVE-2026-45673 has a CVSS v3.1 base score of 6.8 (MODERATE) with vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N.
What CWE is associated with CVE-2026-45673?
CVE-2026-45673 is classified under CWE-330: Use of Insufficiently Random Values (The product uses insufficiently random numbers or values in a security context that depends on unpredictable numbers.).
How can I check Maven dependencies for CVE-2026-45673?
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-xmv7-r254-6q78",
  "modified" : "2026-06-12T19:29:30Z",
  "published" : "2026-06-08T23:02:05Z",
  "aliases" : [ "CVE-2026-45673" ],
  "summary" : "Netty: DNS Cache Poisoning due to Predictable PRNG and Default Static Source Port",
  "details" : "### Summary\nNetty's DNS resolver uses a predictable PRNG for generating DNS transaction IDs and defaults to a static UDP source port. This combination reduces the entropy of DNS queries, enabling DNS Cache Poisoning (Kaminsky attack).\n\n### Details\nTwo factors contribute to this vulnerability in io.netty.resolver.dns:\n- Predictable Query IDs: `DnsQueryIdSpace` manages 16-bit transaction IDs in buckets of 16,384 IDs. It initializes only the first bucket. When an ID is returned, it is pushed back into the bucket at a random index generated by java.util.concurrent.ThreadLocalRandom:\n\n```java\nRandom random = ThreadLocalRandom.current();\nint insertionPosition = random.nextInt(count + 1);\n```\n\nBecause ThreadLocalRandom is a predictable LCG and the resolver operates within a single bucket, the sequence of IDs is predictable once the PRNG state is mathematically recovered.\n\n- Default Static Source Port: `DnsNameResolverBuilder` defaults to a `channelStrategy` of `ChannelPerResolver`. This binds the DatagramChannel once, resulting in a static source port for all subsequent queries.\n\nCombined, a static source port and predictable transaction IDs reduces the entropy required to secure DNS resolution against spoofing.\n\n### Impact\nDNS Cache Poisoning. Downstream applications using the default Netty DNS resolver may connect to malicious IPs, leading to traffic interception or MitM attacks.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-resolver-dns"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "4.2.0.Final"
      }, {
        "fixed" : "4.2.15.Final"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.2.14.Final"
    }
  }, {
    "package" : {
      "ecosystem" : "Maven",
      "name" : "io.netty:netty-resolver-dns"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.1.135.Final"
      } ]
    } ],
    "database_specific" : {
      "last_known_affected_version_range" : "<= 4.1.134.Final"
    }
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/security/advisories/GHSA-xmv7-r254-6q78"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-45673"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/netty/netty"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/releases/tag/netty-4.1.135.Final"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/netty/netty/releases/tag/netty-4.2.15.Final"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-330", "CWE-340" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-06-08T23:02:05Z",
    "nvd_published_at" : "2026-06-12T15:16:27Z"
  }
}