CVE-2026-45416: Netty: SNI handler pre-allocates up to 16 MiB from nine attacker bytes
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.
Other sources
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.
— NVD
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
maven/io.netty:netty-handlerto a version that resolves this vulnerability.Fixed in 4.1.135.Final - Upgrade
Upgrade
maven/io.netty:netty-handlerto a version that resolves this vulnerability.Fixed in 4.2.15.Final - Upgrade
Upgrade
nettyto a version that resolves this vulnerability.Fixed in 4.1.135.Final - Upgrade
Upgrade
nettyto a version that resolves this vulnerability.Fixed in 4.2.15.Final
Event History
Frequently Asked Questions
What is the severity of CVE-2026-45416?
The severity of CVE-2026-45416 is rated as high with a score of 7.5.
How do I fix CVE-2026-45416?
To fix CVE-2026-45416, upgrade to a patched version of netty-handler, specifically netty-4.1.135.Final or netty-4.2.15.Final.
What impact does CVE-2026-45416 have on my system?
CVE-2026-45416 allows for a denial of service attack due to the mishandling of the TLS handshake.
Which versions of netty-handler are affected by CVE-2026-45416?
CVE-2026-45416 affects specific versions of netty-handler prior to the fixes in netty-4.1.135.Final and netty-4.2.15.Final.
What component of netty does CVE-2026-45416 affect?
CVE-2026-45416 specifically affects the SslClientHelloHandler component in netty-handler.