CVE-2026-89044: Netty 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through 4.2.17.Final HTTP Request Smuggling via Transfer-Encoding
Netty versions 4.1.133.Final through 4.1.137.Final and 4.2.13.Final through 4.2.17.Final fail to properly validate the final transfer coding in the Transfer-Encoding header, allowing attackers to smuggle requests by using malformed encoding declarations. Attackers can split Transfer-Encoding headers across multiple lines or use values like 'chunked, xchunked' to bypass validation and decode messages as chunked when the final coding is not chunked, enabling request smuggling attacks.
Affected Software
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Deployments using Netty 4.1.133.Final through 4.1.137.Final or 4.2.13.Final through 4.2.17.Final are affected. The issue is remotely reachable and requires no privileges or user interaction.
What does an attacker need to send to exploit the flaw?
An attacker needs to send an HTTP request with a malformed Transfer-Encoding declaration. Examples include splitting Transfer-Encoding across multiple header lines or using a value such as "chunked, xchunked" so Netty decodes the message as chunked even though the final coding is not chunked.
What is the practical impact of successful exploitation?
Successful exploitation can enable HTTP request smuggling. The stated impact includes limited confidentiality and integrity effects; no availability impact is specified.