h3 before 2.0.1-rc.18 Open Redirect via redirectBack()

{
  "id": "806f2b55ebedba5d9c688cdd8a4e629c5e8f4fa3ea210a368266226497d8a786",
  "url": "https://osv.dev/vulnerability/CVE-2026-86205",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "h3 before 2.0.1-rc.18 Open Redirect via redirectBack()",
    "summary": "h3 versions before 2.0.1-rc.18 contain an open redirect vulnerability in the redirectBack() utility that fails to sanitize protocol-relative paths in the Referer header pathname. Attackers can craft a same-origin URL with a double-slash path segment that passes origin validation but produces a Location header interpreted by browsers as a protocol-relative redirect to an external domain.",
    "evidence": "osv:CVE-2026-86205",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-86205",
      "aliases": [
        "CVE-2026-86205",
        "GHSA-fp4x-ggrf-wmc6"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/h3js/h3",
              "type": "GIT",
              "events": [
                {
                  "introduced": "388b8f06e060a219d11bbc6be7f70f38d8bbea01"
                },
                {
                  "fixed": "cb70e1ba513be827bb3698127bb7d06467412911"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "2.0.1-rc.17"
                      },
                      {
                        "fixed": "2.0.1-rc.18"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "2.0.1-rc.18"
                      }
                    ],
                    "source": "DESCRIPTION"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v2.0.1-rc.17"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-86205.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:29.280312274Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/86xxx/CVE-2026-86205.json",
        "https://github.com/h3js/h3/security/advisories/GHSA-fp4x-ggrf-wmc6",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-86205",
        "https://www.vulncheck.com/advisories/h3-before-2.0.1-rc.18-open-redirect-via-redirectback"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-601"
        ],
        "cna_assigner": "VulnCheck",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/86xxx/CVE-2026-86205.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-86205",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 496272,
  "published_at": "2026-09-06T12:00:25.53+00:00"
}