{"cve":"CVE-2026-54340","nvd":{"published":"2026-07-17T00:16:25.810","modified":"2026-08-05T19:47:02.317","status":"Analyzed","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-400","CWE-770"],"references":["https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063","https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9"],"products":["h2o:h2o"],"source":"nvd","synced_at":"2026-10-19T22:45:36.895656543+00:00"},"epss":{"cve":"CVE-2026-54340","score":0.00493,"percentile":0.42374,"date":"2026-11-01"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}