{"id":"CVE-2026-71554","state":"PUBLISHED","title":"h2: Duplicate Host header could facilitate request smuggling","description":"h2 is a pure-Python implementation of a HTTP/2 protocol stack. Versions up to and including 4.4.0 accept request header blocks containing more than one Host header, and forward every Host header to the consuming application. Where the consumer downgrades HTTP/2 to HTTP/1.1, the resulting request carries two Host header lines, providing a request smuggling primitive. This issue is fixed in version 4.4.1.","publishedAt":"2026-08-06T21:46:43.057Z","updatedAt":"2026-08-08T02:49:30.505Z","severity":{"score":5.3,"label":"Medium","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","source":"GitHub_M"},"assigner":"GitHub_M","products":["python-hyper h2"],"affected":[{"vendor":"python-hyper","product":"h2","versions":[{"version":"< 4.4.1","status":"affected"}]}],"references":["https://github.com/python-hyper/h2/security/advisories/GHSA-6hr6-w5qg-qmwg","https://github.com/python-hyper/h2/commit/292a40829feefda98c8509dcdbbb4a57af9bd6a6"],"weaknesses":["CWE-444"],"ingestedAt":"2026-10-29T20:12:49.727Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/71xxx/CVE-2026-71554.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-71554","state":"PUBLISHED","datePublished":"2026-08-06T21:46:43.057Z","dateUpdated":"2026-08-08T02:49:30.505Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-08-06T21:24:15.376Z"},"containers":{"cna":{"title":"h2: Duplicate Host header could facilitate request smuggling","descriptions":[{"lang":"en","value":"h2 is a pure-Python implementation of a HTTP/2 protocol stack. Versions up to and including 4.4.0 accept request header blocks containing more than one Host header, and forward every Host header to the consuming application. Where the consumer downgrades HTTP/2 to HTTP/1.1, the resulting request carries two Host header lines, providing a request smuggling primitive. This issue is fixed in version 4.4.1."}],"affected":[{"vendor":"python-hyper","product":"h2","versions":[{"version":"< 4.4.1","status":"affected"}]}],"references":[{"url":"https://github.com/python-hyper/h2/security/advisories/GHSA-6hr6-w5qg-qmwg","name":"https://github.com/python-hyper/h2/security/advisories/GHSA-6hr6-w5qg-qmwg","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/python-hyper/h2/commit/292a40829feefda98c8509dcdbbb4a57af9bd6a6","name":"https://github.com/python-hyper/h2/commit/292a40829feefda98c8509dcdbbb4a57af9bd6a6","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"LOW","baseScore":5.3,"baseSeverity":"MEDIUM","confidentialityImpact":"NONE","integrityImpact":"NONE","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"NONE","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-444","lang":"en","description":"CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-08-06T21:46:43.057Z"},"source":{"advisory":"GHSA-6hr6-w5qg-qmwg","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-08T02:49:21.263516Z","id":"CVE-2026-71554","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-08T02:49:30.505Z"}}]}}}