CVE-2026-45416 — Netty: SNI handler pre-allocates up to 16 MiB from nine attacker bytes

Description (CNA)

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.

Affected (CNA)

Vendor / product	Versions
netty / netty	affected >= 4.2.0.Final, < 4.2.15.Final; affected < 4.1.135.Final

CWE

CWE-770

References

ADP enrichment

CISA-ADP

No English description supplied.

No references supplied.

redhat-SADP

A flaw was found in Netty, a network application framework. A remote attacker can exploit this vulnerability by sending a crafted TLS (Transport Layer Security) ClientHello message. This can lead to an eager allocation of a large memory buffer, causing a Denial of Service (DoS) due to excessive memory consumption. The issue occurs in the `SslClientHelloHandler.decode()` method when processing the TLS handshake length.