---
id: GHSA-mfg7-5gfp-c4w3
title: 'Netty: Memory Leak in DNS Record Decoder via Malformed Domain Names'
summary: 'Netty: Memory Leak in DNS Record Decoder via Malformed Domain Names'
severity: medium
cvss: 5.3
cwe:
  - CWE-772
vendor: netty
product: 'io.netty:netty-codec-dns'
ecosystem: maven
affected:
  - 'io.netty:netty-codec-dns >= 4.2.0.Final, <= 4.2.15.Final'
  - 'io.netty:netty-codec-dns <= 4.1.135.Final'
patched:
  - 'io.netty:netty-codec-dns 4.2.16.Final'
  - 'io.netty:netty-codec-dns 4.1.136.Final'
published: '2026-07-24'
updated: '2026-07-24'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-mfg7-5gfp-c4w3'
references:
  - url: 'https://github.com/netty/netty/security/advisories/GHSA-mfg7-5gfp-c4w3'
  - url: 'https://github.com/netty/netty/pull/17063'
  - url: 'https://github.com/netty/netty/pull/17065'
  - url: >-
      https://github.com/netty/netty/commit/5b68c61f37aa4a3045cba624cbea239655c9003b
  - url: >-
      https://github.com/netty/netty/commit/bb2ff68a1fb71cb4b0eb9a9e17b66c52aff680c6
  - url: 'https://github.com/netty/netty/releases/tag/netty-4.1.136.Final'
  - url: 'https://github.com/netty/netty/releases/tag/netty-4.2.16.Final'
  - url: 'https://github.com/advisories/GHSA-mfg7-5gfp-c4w3'
tags:
  - ghsa
  - maven
ingestedAt: '2026-07-24T17:34:27.507Z'
---

## Overview

### Summary
A memory leak can be caused in Netty's DNS codec by sending malicious DNS packets containing invalid domain names. Because the leak occurs incrementally per packet, sustained malicious requests will cause a gradual Denial of Service.

### Details
Inside `io.netty.handler.codec.dns.AbstractDnsRecord`, the parsed domain name string is passed to `IDN.toASCII(name)`. If the domain name contains characters that violate IDNA rules, `IDN.toASCII` throws an `IllegalArgumentException`.

Because this exception occurs inside the constructor before the `DnsRecord` instance can assign the buffer to its content field for later release, the ByteBuf whose reference count was incremented (or newly allocated) is never released, resulting in a direct memory leak.

There are several places where variants of this leak happen:
- `io.netty.handler.codec.dns.DefaultDnsRecordDecoder#decodeRecord(java.lang.String, io.netty.handler.codec.dns.DnsRecordType, int, long, io.netty.buffer.ByteBuf, int, int)` invokes `in.retainedDuplicate()` or creates a new buffer `out` when constructing `DefaultDnsRawRecord`
- `io.netty.handler.codec.dns.DnsCodecUtil#decompressDomainName` allocates a new `ByteBuf` and passes it to `encodeDomainName()`. If the decompressed domain name contains a null byte (`\0`), `encodeDomainName()` throws an `IllegalArgumentException`, leaking the newly allocated buffer.

### Impact
Resource Exhaustion. Any application utilizing Netty's DnsRecordDecoder (such as DnsNameResolver or custom DNS servers) is vulnerable.

## Affected packages

- `io.netty:netty-codec-dns >= 4.2.0.Final, <= 4.2.15.Final`
- `io.netty:netty-codec-dns <= 4.1.135.Final`

## Remediation

Upgrade to a patched release:

- `io.netty:netty-codec-dns 4.2.16.Final`
- `io.netty:netty-codec-dns 4.1.136.Final`