Netty has Insufficient Bailiwick Validation for NS Records

Summary

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.

Timeline

1. Jun 12, 2026, 12:00 AM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

2. Jun 12, 2026, 2:33 PM UTCCVE published
3. Sep 18, 2026, 12:04 PM UTCRecord last updated

Affected versions

• netty netty

  From 4.2.0.Final · fixed in 4.2.15.Final; fixed in 4.1.135.Final

• io.netty:netty-resolver-dnsMaven

  From 4.2.0.Final · fixed in 4.2.15.Final

• io.netty:netty-resolver-dnsMaven

  fixed in 4.1.135.Final

References 3