Summary
Netty has Insufficient Bailiwick Validation for NS Records
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).
Details
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.
This means if the resolver queries evil.co.uk., it will accept an NS record claiming authority over co.uk.. Subsequently, the handleWithAdditional method caches the associated A records from the ADDITIONAL section directly into the authoritativeDnsServerCache under the parent domain's key (co.uk.). 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 co.uk..
The io.netty.resolver.dns.DnsResolveContext.AuthoritativeNameServerList#cache method only prevents caching if the record is for the root zone (dots == 1).
Impact
DNS Cache Poisoning. Any application using Netty's DNS resolver is impacted.
CVE-2026-47691 has a CVSS score of 8.7 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (4.2.15.Final, 4.1.135.Final); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
io.netty:netty-resolver-dns to 4.2.15.Final or later; io.netty:netty-resolver-dns to 4.1.135.Final or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-47691? CVE-2026-47691 is a high-severity security vulnerability in io.netty:netty-resolver-dns (maven), affecting versions >= 4.2.0.Final, <= 4.2.14.Final. It is fixed in 4.2.15.Final, 4.1.135.Final.
- How severe is CVE-2026-47691? CVE-2026-47691 has a CVSS score of 8.7 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of io.netty:netty-resolver-dns are affected by CVE-2026-47691? io.netty:netty-resolver-dns (maven) versions >= 4.2.0.Final, <= 4.2.14.Final is affected.
- Is there a fix for CVE-2026-47691? Yes. CVE-2026-47691 is fixed in 4.2.15.Final, 4.1.135.Final. Upgrade to this version or later.
- Is CVE-2026-47691 exploitable, and should I be worried? Whether CVE-2026-47691 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-47691 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-47691?
- Upgrade
io.netty:netty-resolver-dnsto 4.2.15.Final or later - Upgrade
io.netty:netty-resolver-dnsto 4.1.135.Final or later
- Upgrade