Executive brief
Netty is a widely used networking framework that helps Java applications communicate over the internet. A vulnerability in how it handles web requests allows an attacker to 'smuggle' hidden commands inside a legitimate-looking request. This can lead to unauthorized access to data or the ability to bypass security controls when the application is used behind a proxy server.
Technical details
An HTTP Request Smuggling vulnerability exists in Netty's HTTP codec due to improper validation of the Transfer-Encoding header. Specifically, Netty incorrectly treats a request as chunked even when 'chunked' is not the final encoding (e.g., 'Transfer-Encoding: chunked, identity'), violating RFC 9112. If a front-end proxy ignores this malformed header and relies on Content-Length instead, an attacker can embed a second, 'smuggled' request within the body of the first. This allows for bypass of security filters or unauthorized access to other users' sessions. The issue is resolved in versions 4.2.13.Final and 4.1.133.Final.
Affected products
- Netty netty-codec-http <= 4.2.12.Final, <= 4.1.132.Final
Timeline
- 2026-05-05: advisory: GitHub Security Advisory published by maintainers
- 2026-05-13: disclosed: CVE published to NVD
- 2026-05-13: patched: Fixes released in versions 4.2.13.Final and 4.1.133.Final