Netty HttpProxyHandler Header Injection (4.2.13.Final/4.1.133.Final)
CVE-2026-42578 Published on May 13, 2026
Netty: HTTP Header Injection via HttpProxyHandler Disabled Validation
Netty is an asynchronous, event-driven network application framework. Prior to 4.2.13.Final and 4.1.133.Final, Netty's HttpProxyHandler constructs HTTP CONNECT requests with header validation explicitly disabled. The newInitialMessage() method creates headers using DefaultHttpHeadersFactory.headersFactory().withValidation(false), then adds user-provided outboundHeaders without any CRLF validation. This allows an attacker who can influence the outbound headers to inject arbitrary HTTP headers into the CONNECT request sent to the proxy server. This vulnerability is fixed in 4.2.13.Final and 4.1.133.Final.
Weakness Type
What is a HTTP Response Splitting Vulnerability?
The software receives data from an upstream component, but does not neutralize or incorrectly neutralizes CR and LF characters before the data is included in outgoing HTTP headers.
CVE-2026-42578 has been classified to as a HTTP Response Splitting vulnerability or weakness.
Products Associated with CVE-2026-42578
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Affected Versions
netty:- Version >= 4.2.0.Alpha1, < 4.2.13.Final is affected.
- Version < 4.1.133.Final is affected.