CVE-2026-42578: Netty: HTTP Header Injection via HttpProxyHandler Disabled Validation

Severity: high (CVSS 7.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.1% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-05-13 · updated 2026-09-18
Weakness: CWE-113

Description

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.

Affected products

netty: before 4.1.133; from 4.2.0 before 4.2.13 — fixed in 4.1.133, 4.2.13

How to fix

Upgrade to a fixed version: netty 4.1.133, 4.2.13. Check the vendor advisory for mitigations.

References

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