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Vulnerability · Published May 13, 2026 · Assigned by GitHub_M

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

High 7.5

In plain English

A high-severity security flaw in netty from netty. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 1.1% (higher than 65% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High
Exploit odds (30 days)1.1%top 35.2% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

Official 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 packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12nettyno fix listedDEBIAN-CVE-2026-42578
Debian:13nettyno fix listedDEBIAN-CVE-2026-42578
Debian:14nettyno fix listedDEBIAN-CVE-2026-42578
Mavenio.netty:netty-handler-proxy4.2.13.FinalGHSA-45q3-82m4-75jr
Mavenio.netty:netty-handler-proxy4.1.133.FinalGHSA-45q3-82m4-75jr
Ubuntu:25.10nettyno fix listedUBUNTU-CVE-2026-42578
Ubuntu:26.10nettyno fix listedUBUNTU-CVE-2026-42578

Affected products (as reported)

VendorProductVersions
netty netty >= 4.2.0.Alpha1, < 4.2.13.Final< 4.1.133.Final

Weakness: CWE-113, CWE-93 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

References