CVE-2026-47691 Netty has Insufficient Bailiwick Validation for NS Records
Netty's insufficient bailiwick validation allows attackers to poison DNS caches for parent domains, leading to potential traffic redirection or data interception.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-47691?
CVE-2026-47691 is a high-severity vulnerability in Netty Netty, published on 12 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-47691?
4 open source packages ship an affected version, including io.netty:netty-resolver-dns. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
io.netty:netty-resolver-dns Maven | All versions | 4.1.135.Final |
io.netty:netty-resolver-dns Maven | All versions | 4.1.135.Final |
io.netty:netty-resolver-dns Maven | From 4.2.0.Final | 4.2.15.Final |
io.netty:netty-resolver-dns Maven | From 4.2.0.Final | 4.2.15.Final |
Products include Netty Netty.
How do I fix CVE-2026-47691?
Upgrade io.netty:netty-resolver-dns to a fixed version for your release line: 4.1.135.Final or 4.2.15.Final.
Is CVE-2026-47691 being exploited?
There is no known exploitation of CVE-2026-47691 in the wild and no public exploit code.
Other vulnerabilities in Netty Netty
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- CVE-2026-75596 Netty: Fragmented ClientHello records trigger quadratic pre-handshake reassembly in default SNI parsing
- CVE-2026-59901 Netty Bzip2Decoder: Infinite Loop in RLE State Machine Leads to Event-Loop Thread Hang
- CVE-2026-55851 Netty codec-haproxy: Signed-Byte Sentinel Collision in HAProxyMessageDecoder Leads to Unbounded Memory Exhaustion
- CVE-2026-56745 Netty SpdyHttpDecoder: ByteBuf Reference Leak on RST_STREAM Leads to Native Memory Exhaustion
Sources
Also known as CLEANSTART-2026-GJ61337, CLEANSTART-2026-QG30470, CLEANSTART-2026-TY33205, CLEANSTART-2026-XI69857, DEBIAN-CVE-2026-47691, ECHO-d6a5-6169-94ec and 82 more.