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NettyApplication

CVE-2026-47691

CRITICAL · 10.0 CVSS v3.1 Published 2026-06-12
Fix available
A fix is available. Upgrade to 4.1.135 / 4.2.15 or later.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Netty is a network application framework for development of protocol servers and clients. Prior to versions 4.1.135.Final and 4.2.15.Final, Netty's `DnsResolveContext` insufficiently validates the bailiwick of NS records, enabling DNS Cache Poisoning. An attacker controlling an authoritative name server for a subdomain can poison the cache for parent domains (like `.co.uk`). In `io.netty.resolver.dns.DnsResolveContext.AuthoritativeNameServerList#add` method accepts any NS record from the AUTHORITY section as long as the record's name is a suffix of the questionName. Subsequently, the `handleWithAdditional` method caches the associated A records from the ADDITIONAL section directly into the `authoritativeDnsServerCache` under the parent domain's key. This bypasses standard bailiwick rules, where a server authoritative for a subdomain should not be trusted to provide authoritative records for its parent. The poisoned cache is then used for all future resolutions under the parent domain's key. Versions 4.1.135.Final and 4.2.15.Final patch the issue.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Netty's DnsResolveContext insufficiently validates the bailiwick of NS records in the AUTHORITY section. The add method accepts any NS record where the record's name is a suffix of the questionName, and handleWithAdditional subsequently caches associated A records from the ADDITIONAL section under the parent domain's key, bypassing standard bailiwick rules. This allows an attacker controlling an authoritative nameserver for a subdomain to poison the cache for parent domains.

MitigationUpgrade Netty to version 4.1.135.Final or 4.2.15.Final or later, which contains proper bailiwick validation for NS records.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
NettyApplication
Affected:< 4.1.135>= 4.2.0, < 4.2.15

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify Netty version in use
    Inspect your project's dependency manifest (pom.xml, build.gradle, package-lock.json, or Maven/Gradle dependency tree). Look for io.netty:netty-all or netty-bom and note the version number.
    Affected if The version is lower than 4.1.135 or between 4.2.0 and 4.2.14 inclusive.
  2. Confirm DNS resolution is in use
    Search your codebase for imports or usage of Netty DNS classes such as DnsNameResolver, DnsResolver, DnsResolveContext, orDnsAddressResolverGroup. Also check for bootstrap/resolver configuration referencing DnsNameResolverBuilder.
    Affected if The application instantiates or configures a Netty-based DNS resolver.
  3. Check for DNS caching configuration
    Inspect your Netty DNS resolver configuration for any custom caching settings. Look for DnsCache instances or custom DnsCache implementations passed to DnsNameResolverBuilder with cache method.
    Affected if A custom or default DNS cache is configured and the resolver is used for recursive lookups.
  4. Verify DNS query patterns
    Review application logs or network traces to confirm DNS queries are being performed using Netty's DnsNameResolver, particularly for domains where the application may query upstream resolvers.
    Affected if The resolver performs recursive or iterative DNS queries where it processes AUTHORITY and ADDITIONAL sections from responses.

If your Netty version falls below 4.1.135 or is between 4.2.0 and 4.2.14 AND your application uses Netty's DnsNameResolver for DNS lookups, then your environment is affected by this cache poisoning vulnerability.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 4.1.135 / 4.2.15 or later
Fixed in 4.1.1354.2.15
Interim mitigation

Upgrade Netty to version 4.1.135.Final or 4.2.15.Final or later, which contains proper bailiwick validation for NS records.

Recommended fix High confidence

Netty 4.1.135.Final or 4.2.15.Final (depending on which branch is in use)

  1. 1. Identify the current Netty version in use by checking project dependencies (Maven pom.xml, Gradle build.gradle, or similar)
  2. 2. For Maven projects: Update the netty dependency version in pom.xml to 4.1.135.Final (for 4.1.x line) or 4.2.15.Final (for 4.2.x line)
  3. 3. For Gradle projects: Update the netty version in build.gradle to '4.1.135.Final' or '4.2.15.Final'
  4. 4. Run dependency resolution to verify the upgrade: `mvn dependency:tree` (Maven) or `./gradlew dependencies` (Gradle)
  5. 5. Rebuild the project and run all tests to ensure compatibility
  6. 6. Deploy the updated application

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Netty Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing12.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,760
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-47691 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data