{"id":"CVE-2026-100663","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-100663","generatedAt":"2026-10-28T05:26:51.212Z","title":"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.","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.","published":"2026-09-26T14:16:49.000Z","lastModified":"2026-09-28T19:16:46.000Z","status":"Deferred","sourceIdentifier":"disclosure@vulncheck.com","cvss":{"version":"4.0","score":8.7,"severity":"HIGH","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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/M"},"cwe":["CWE-20"],"affected":[],"epss":{"score":0.00301,"percentile":0.2272,"date":"2026-10-27","history":[{"date":"2026-09-27","score":0.00301,"percentile":0.20474}]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.30%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[{"kind":"new","label":"New CVE","at":"2026-09-26T14:16:49.000Z","detail":{"score":"8.7","severity":"HIGH","publishedAt":"2026-09-26T14:16:49.400Z"},"summary":"New CVE, high severity (CVSS 8.7)."}],"references":[{"url":"https://github.com/netty/netty/security/advisories/GHSA-jgph-cgq3-c627","source":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/netty-http-1-connect-authority-form-mistranslated-to-malformed-http-3","source":"disclosure@vulncheck.com"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-100663","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}