Netty up to 0.x/2.1 Front-End request smuggling

Summaryinfo

A vulnerability identified as problematic has been detected in Netty up to 0.x/2.1. This affects an unknown function of the component Front-End. The manipulation leads to request smuggling. This vulnerability is documented as CVE-2026-50020. The attack can be initiated remotely. There is not any exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in Netty up to 0.x/2.1. This issue affects some unknown functionality of the component Front-End. The manipulation with an unknown input leads to a request smuggling vulnerability. Using CWE to declare the problem leads to CWE-444. The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination. Impacted is integrity. 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, before reading the first request-line, `HttpObjectDecoder` skips every byte for which `Character.isISOControl(b)` is `true` (0x00–0x1F and 0x7F) as well as all whitespace. RFC 9112 §2.2 only asks servers to ignore empty CRLF lines preceding the request-line — a carefully scoped robustness allowance intended to handle HTTP/1.0 POST workarounds. Silently absorbing NUL bytes, SOH, STX, and other non-CRLF control characters goes significantly beyond this, and can be exploited for request-boundary confusion in pipelined or multiplexed transports where a front-end component treats those bytes differently. Versions 4.1.135.Final and 4.2.15.Final patch the issue.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-50020 since 06/03/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. The technical details are unknown and an exploit is not publicly available.

Upgrading to version 4.1.135.Final or 4.2.15.Final eliminates this vulnerability. The upgrade is hosted for download at github.com.

The vulnerability is also documented in the vulnerability database at CERT Bund (WID-SEC-2026-1814). Be aware that VulDB is the high quality source for vulnerability data.

Affected

• Open Source Netty

Productinfo

Name

• Netty

Version

• 0.x
• 2.0
• 2.1

Website

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

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Be aware that VulDB is the high quality source for vulnerability data.

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