CVE-2026-44249 Netty has an IPv6 Subnet Filter Bypass via Incorrect Comparator Masking
Attackers can bypass IPv6 subnet access restrictions in Netty due to incorrect masking logic, allowing unauthorized access from valid public IPs.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-44249?
CVE-2026-44249 is a high-severity vulnerability in Netty Netty, published on 11 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. In netty-handler prior to versions 4.1.135.Final and 4.2.15.Final, an attacker can bypass IPv6 subnet rules due to an incorrect masking operation in IpSubnetFilterRule.compareTo(). Valid public IP addresses can bypass the restrictions. Versions 4.1.135.Final and 4.2.15.Final patch the issue.
Which versions are affected by CVE-2026-44249?
4 open source packages ship an affected version, including io.netty:netty-handler. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
io.netty:netty-handler Maven | All versions | 4.1.135.Final |
io.netty:netty-handler Maven | All versions | 4.1.135.Final |
io.netty:netty-handler Maven | From 4.2.0.Final | 4.2.15.Final |
io.netty:netty-handler Maven | From 4.2.0.Final | 4.2.15.Final |
Products include Netty Netty.
How do I fix CVE-2026-44249?
Upgrade io.netty:netty-handler to a fixed version for your release line: 4.1.135.Final or 4.2.15.Final.
Is CVE-2026-44249 being exploited?
There is no known exploitation of CVE-2026-44249 in the wild and no public exploit code.
Other vulnerabilities in Netty Netty
- CVE-2026-75595 Netty: SNI Routing Bypass via Fragmented TLS ClientHello Causing Fallback to Default SslContext
- 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-IH49300, CLEANSTART-2026-OD95693, CLEANSTART-2026-PH55510, CLEANSTART-2026-SX32964, CLEANSTART-2026-UH79636, DEBIAN-CVE-2026-44249 and 128 more.