{"id":"CVE-2026-100663","state":"PUBLISHED","title":"Netty HTTP/1 CONNECT authority-form mistranslated to malformed HTTP/3","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.","publishedAt":"2026-09-26T13:23:29.751Z","updatedAt":"2026-09-28T18:48:51.788Z","severity":{"score":8.7,"label":"High","version":"4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N","source":"VulnCheck"},"assigner":"VulnCheck","products":["netty netty"],"affected":[{"vendor":"netty","product":"netty","packageURL":"pkg:maven/io.netty/netty-codec-http3","defaultStatus":"unaffected","versions":[{"version":"4.2.2.Final","status":"affected","lessThan":"4.2.18.Final","versionType":"custom"},{"version":"4.2.18.Final","status":"unaffected","versionType":"custom"}]}],"references":["https://github.com/netty/netty/security/advisories/GHSA-jgph-cgq3-c627","https://www.vulncheck.com/advisories/netty-http-1-connect-authority-form-mistranslated-to-malformed-http-3"],"weaknesses":["CWE-20"],"ingestedAt":"2026-10-29T20:10:13.529Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/100xxx/CVE-2026-100663.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-100663","state":"PUBLISHED","datePublished":"2026-09-26T13:23:29.751Z","dateUpdated":"2026-09-28T18:48:51.788Z","assignerShortName":"VulnCheck","assignerOrgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","dateReserved":"2026-09-26T02:33:59.039Z"},"containers":{"cna":{"title":"Netty HTTP/1 CONNECT authority-form mistranslated to malformed HTTP/3","descriptions":[{"lang":"en","value":"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."}],"affected":[{"vendor":"netty","product":"netty","packageURL":"pkg:maven/io.netty/netty-codec-http3","defaultStatus":"unaffected","versions":[{"version":"4.2.2.Final","status":"affected","lessThan":"4.2.18.Final","versionType":"custom"},{"version":"4.2.18.Final","status":"unaffected","versionType":"custom"}]}],"references":[{"url":"https://github.com/netty/netty/security/advisories/GHSA-jgph-cgq3-c627","tags":["vendor-advisory"],"name":"GitHub Security Advisory (GHSA-jgph-cgq3-c627)"},{"url":"https://www.vulncheck.com/advisories/netty-http-1-connect-authority-form-mistranslated-to-malformed-http-3","name":"VulnCheck Advisory: Netty HTTP/1 CONNECT authority-form mistranslated to malformed HTTP/3","tags":["third-party-advisory"]}],"metrics":[{"format":"CVSS","cvssV4_0":{"version":"4.0","vectorString":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N","attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"HIGH","vulnAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","baseScore":8.7,"baseSeverity":"HIGH"}},{"format":"CVSS","cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N","attackVector":"NETWORK","attackComplexity":"LOW","privilegesRequired":"NONE","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"NONE","integrityImpact":"HIGH","availabilityImpact":"NONE","baseScore":7.5,"baseSeverity":"HIGH"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-20","lang":"en","description":"Improper Input Validation","type":"CWE"}]}],"providerMetadata":{"shortName":"VulnCheck","orgId":"83251b91-4cc7-4094-a5c7-464a1b83ea10","dateUpdated":"2026-09-27T16:27:48.867Z"},"datePublic":"2026-09-10T00:00:00.000Z","cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:a:netty:netty:*:*:*:*:*:*:*:*","versionStartIncluding":"4.2.2.final","versionEndExcluding":"4.2.18.final"}]}]}],"credits":[{"lang":"en","value":"rexpository","type":"reporter"}],"x_generator":{"engine":"vulncheck-endgame"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-09-28T18:48:08.213536Z","id":"CVE-2026-100663","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-09-28T18:48:51.788Z"}}]}}}