Netty prior 4.1.135.Final/4.2.15.Final TLS Handshake SslClientHelloHandler.decode allocation of resources

Summaryinfo

A vulnerability marked as problematic has been reported in Netty. This issue affects the function SslClientHelloHandler.decode of the component TLS Handshake Handler. Performing a manipulation results in allocation of resources. This vulnerability is known as CVE-2026-45416. Remote exploitation of the attack is possible. No exploit is available. It is suggested to upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, was found in Netty. This affects the function SslClientHelloHandler.decode of the component TLS Handshake Handler. The manipulation with an unknown input leads to a allocation of resources vulnerability. CWE is classifying the issue as CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. This is going to have an impact on availability. The summary by CVE is:

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.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-45416 since 05/12/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 4.1.135.Final or 4.2.15.Final eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-1814). If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Affected

• Open Source Netty

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• Netty

Website

• Product: https://github.com/netty/netty/

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If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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