Netty up to 8.0 writeToken verification of source

Summaryinfo

A vulnerability identified as problematic has been detected in Netty up to 8.0. Affected is the function writeToken. The manipulation leads to verification of source. This vulnerability is traded as CVE-2026-44894. It is possible to initiate the attack remotely. There is no exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in Netty up to 8.0 and classified as problematic. This issue affects the function writeToken. The manipulation with an unknown input leads to a verification of source vulnerability. Using CWE to declare the problem leads to CWE-940. The product establishes a communication channel to handle an incoming request that has been initiated by an actor, but it does not properly verify that the request is coming from the expected origin. Impacted is integrity. The summary by CVE is:

Netty is a network application framework for development of protocol servers and clients. NoQuicTokenHandler is the tokenHandler used when the application does not set one. Prior to version 4.2.15.Final, its writeToken() returns false (server will not send Retry — acceptable), but validateToken() unconditionally `return 0`. In QuicheQuicServerCodec.handlePacket(), a non-negative return from validateToken() is interpreted as 'token is valid, ODCID starts at offset 0', causing the server to call quiche_accept as if the client's address had been validated by a Retry round-trip. Per RFC 9000 §8.1, a validated address lifts the 3× anti-amplification send limit. Thus any attacker who includes ANY non-empty token bytes in an Initial packet — with a spoofed victim source IP — causes the Netty server to treat the victim as validated and reflect full-size handshake flights (certificates, etc.) toward it without the 3× cap. The correct 'no token handler' semantics would be to return -1 (invalid) so the normal un-validated path and amplification limit apply. Version 4.2.15.Final patches the issue.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2026-44894 since 05/07/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available.

Upgrading to version 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

Productinfo

Name

• Netty

Version

• 8.0

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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