{"id":"CVE-2026-100663","title":"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","summary":"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. T…","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","cwe":["CWE-20","CWE-444"],"vendor":"netty","product":"netty","affected":["netty >= 4.2.2.Final < 4.2.18.Final"],"published":"2026-09-26","updated":"2026-09-28","sourceUpdated":"2026-09-28T19:16:45.613","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-100663","references":[{"url":"https://github.com/netty/netty/security/advisories/GHSA-jgph-cgq3-c627","label":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/netty-http-1-connect-authority-form-mistranslated-to-malformed-http-3","label":"disclosure@vulncheck.com"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-100663.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-100663"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2541850"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-100663"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-100663"}],"tags":["nvd","cve.org","exploit-available","csaf","vex","red-hat"],"exploitAvailable":true,"ssvc":{"exploitation":"poc","automatable":"no","technicalImpact":"partial","timestamp":"2026-09-28T18:48:08.213536Z"},"ingestedAt":"2026-09-26T13:33:20.916Z","epss":0.00301,"epssPercentile":0.2272,"slug":"CVE-2026-100663","body":"## Overview\n\nNetty'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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · Important · affected: Red Hat OpenShift Dev Spaces · no fix planned: Red Hat OpenShift Dev Spaces · updated 2026-09-29 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-100663.json)","depth":"midnight","depthScore":53,"depthScoreParts":{"impact":41.3,"likelihood":0.1,"exploitation":12,"ransomware":0},"changes":[{"seq":212106,"id":"CVE-2026-100663","ts":1790623193338,"field":"exploit_available","old":"false","new":"true"}]}