{"id":"CVE-2026-54340","summary":"h2o has HTTP/2 state amplification","details":"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.","aliases":["GHSA-qcrr-wrhc-pgq9"],"modified":"2026-08-12T03:51:19.104332503Z","published":"2026-07-16T23:29:50.799Z","database_specific":{"cwe_ids":["CWE-400","CWE-770"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54340.json","unresolved_ranges":[{"extracted_events":[{"fixed":"9265bdd"}],"source":"AFFECTED_FIELD"}],"cna_assigner":"GitHub_M"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54340.json"},{"type":"ADVISORY","url":"https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-54340"},{"type":"FIX","url":"https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/h2o/h2o","events":[{"introduced":"0"},{"fixed":"9265bdd9a996ed992681055e3996baf3e09d2063"}],"database_specific":{"source":"REFERENCES"}}],"versions":["v1.7.0","v1.7.0-beta5","v1.7.0-beta4","v1.7.0-beta3","v1.7.0-beta2","v1.7.0-beta1","v1.6.0","v1.6.0-beta2","v1.6.0-beta1","v1.5.3","v1.5.2","v1.5.1","v1.5.0","v1.5.0-beta4","v1.5.0-beta3","v1.5.0-beta2","v1.5.0-beta1","v1.4.2","v1.4.1","v1.4.0","v1.3.1","v1.3.0","v1.3.0-beta1","v1.2.0","v1.1.1","v1.1.0","v1.0.1","v0.9.2","v0.9.1"],"database_specific":{"source":"https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-54340.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}]}