{"id":"CVE-2026-100663","published":"2026-09-26T14:16:49.400","lastModified":"2026-09-28T19:16:45.613","description":"Netty's HTTP/3 codec (io.netty:netty-codec-http3) from 4.2.2.Final through 4.2.17.Final does not special-case HTTP/1 CONNECT authority-form request-targets when converting HTTP/1 messages to HTTP/3 in HttpConversionUtil.toHttp3Headers. The authority-form target (e.g., \"CONNECT trusted.example:443\") is parsed as a URI, so its host is emitted as :scheme, :path is set to \"/\", and the HTTP/1 Host header is used as :authority; if no Host header is present the CONNECT target is dropped. In a Netty-based HTTP/1-to-HTTP/3 proxy or gateway, a remote client can send a CONNECT request whose Host header names a different authority than the request-target, producing a malformed HTTP/3 CONNECT whose tunnel :authority is attacker-controlled. This can bypass tunnel allow-lists, egress policy, backend selection, or audit controls that validate the HTTP/1 CONNECT request-target before forwarding over HTTP/3. The issue is fixed in 4.2.18.Final.","cvssScore":7.5,"cvssSeverity":"HIGH","cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","cwes":["CWE-20"],"vendors":[],"products":[],"references":[{"url":"https://github.com/netty/netty/security/advisories/GHSA-jgph-cgq3-c627","tags":[]},{"url":"https://www.vulncheck.com/advisories/netty-http-1-connect-authority-form-mistranslated-to-malformed-http-3","tags":[]}],"exploitRefs":[{"url":"https://github.com/netty/netty/security/advisories/GHSA-jgph-cgq3-c627","tags":[]}],"hasPoc":true,"ai":null}