CVE-2026-45416 Netty: SNI handler pre-allocates up to 16 MiB from nine attacker bytes
Attackers can cause memory exhaustion and denial of service by sending small TLS ClientHello packets that trigger large pre-allocations in Netty's SNI handler.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-45416?
CVE-2026-45416 is a high-severity denial of service 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, SslClientHelloHandler.decode() reads the 24-bit TLS handshake length and, when the ClientHello does not fit in the first record, eagerly allocates `ctx.alloc().buffer(handshakeLength)` (line 161). The guard at line 140 is `handshakeLength > maxClientHelloLength && maxClientHelloLength != 0`, and the commonly-used SniHandler/AbstractSniHandler constructors (SniHandler(Mapping), SniHandler(AsyncMapping), AbstractSniHandler()) pass maxClientHelloLength=0 and handshakeTimeoutMillis=0, so the length guard is disabled and no timeout is scheduled. A 16 MiB request exceeds the default pooled chunk size and becomes a huge/unpooled allocation performed immediately. The buffer is retained in the handler until the channel closes. Versions 4.1.135.Final and 4.2.15.Final patch the issue.
Weakness: CWE-770
Which versions are affected by CVE-2026-45416?
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-2026-45416?
Upgrade io.netty:netty-handler to a fixed version for your release line: 4.1.135.Final or 4.2.15.Final.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-45416 being exploited?
There is no known exploitation of CVE-2026-45416 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-FY04918, CLEANSTART-2026-IR80784, CLEANSTART-2026-SE44846, CLEANSTART-2026-TV10241, CLEANSTART-2026-YI20813, DEBIAN-CVE-2026-45416 and 128 more.