{"id":"CVE-2026-54340","state":"PUBLISHED","title":"h2o has HTTP/2 state amplification","description":"h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 9265bdd, there is an HTTP/2 state amplification issue that combines HPACK decompression amplification with Slowloris-style stream stalling. Amplified decoded header state can be retained by stalled HTTP/2 streams, and depending on the configuration, additional limits are needed to bound decoded header state and prevent attack. This issue has been fixed by commit 9265bdd.","publishedAt":"2026-07-16T23:29:50.799Z","updatedAt":"2026-07-17T18:06:19.274Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"GitHub_M"},"assigner":"GitHub_M","products":["h2o h2o"],"affected":[{"vendor":"h2o","product":"h2o","versions":[{"version":"< 9265bdd","status":"affected"}]}],"references":["https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9","https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063"],"weaknesses":["CWE-400","CWE-770"],"ingestedAt":"2026-10-29T20:12:24.861Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/54xxx/CVE-2026-54340.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-54340","state":"PUBLISHED","datePublished":"2026-07-16T23:29:50.799Z","dateUpdated":"2026-07-17T18:06:19.274Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-06-12T19:23:22.316Z"},"containers":{"cna":{"title":"h2o has HTTP/2 state amplification","descriptions":[{"lang":"en","value":"h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 9265bdd, there is an HTTP/2 state amplification issue that combines HPACK decompression amplification with Slowloris-style stream stalling. Amplified decoded header state can be retained by stalled HTTP/2 streams, and depending on the configuration, additional limits are needed to bound decoded header state and prevent attack. This issue has been fixed by commit 9265bdd."}],"affected":[{"vendor":"h2o","product":"h2o","versions":[{"version":"< 9265bdd","status":"affected"}]}],"references":[{"url":"https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9","name":"https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063","name":"https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":7.5,"baseSeverity":"HIGH","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:H","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-400","lang":"en","description":"CWE-400: Uncontrolled Resource Consumption","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-770","lang":"en","description":"CWE-770: Allocation of Resources Without Limits or Throttling","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-07-16T23:29:50.799Z"},"source":{"advisory":"GHSA-qcrr-wrhc-pgq9","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-07-17T15:26:10.914862Z","id":"CVE-2026-54340","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":"2026-07-17T18:06:19.274Z"}}]}}}