h2o has HTTP/2 state amplification

{
  "id": "bb4358b6d9a9fdbdc4f7729f80fe8b893e0af92cf54f60cf6951e20dd9831749",
  "url": "https://osv.dev/vulnerability/CVE-2026-54340",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "h2o has HTTP/2 state amplification",
    "summary": "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.",
    "evidence": "osv:CVE-2026-54340",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-54340",
      "aliases": [
        "CVE-2026-54340",
        "GHSA-qcrr-wrhc-pgq9"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/h2o/h2o",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "9265bdd"
                },
                {
                  "fixed": "9265bdd9a996ed992681055e3996baf3e09d2063"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "9265bdd"
                      }
                    ],
                    "source": "DESCRIPTION"
                  },
                  {
                    "range": [
                      {
                        "fixed": "9265bdd9a996ed992681055e3996baf3e09d2063"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            },
            {
              "repo": "https://github.com/h2oai/h2o-3",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "fixed": "9265bdd"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "9265bdd"
                      }
                    ],
                    "source": "DESCRIPTION"
                  }
                ]
              }
            }
          ],
          "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"
          }
        }
      ],
      "modified": "2026-10-28T02:30:24.736226205Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54340.json",
        "https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-54340",
        "https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-400",
          "CWE-770"
        ],
        "cna_assigner": "GitHub_M",
        "unresolved_ranges": [
          {
            "extracted_events": [
              {
                "range": [
                  {
                    "fixed": "9265bdd"
                  }
                ],
                "source": "AFFECTED_FIELD",
                "strategy": "StringRangeExpression"
              }
            ]
          }
        ],
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/54xxx/CVE-2026-54340.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-54340",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 491531,
  "published_at": "2026-07-16T23:29:50.799+00:00"
}