AshPhoenix get_subdomain maps a crafted or differently-cased Host header to an arbitrary tenant

{
  "id": "8171f9a28305d0123b138d866551f729053da7baa996f4bd254fb2f50ab39afe",
  "url": "https://osv.dev/vulnerability/CVE-2026-82726",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "AshPhoenix get_subdomain maps a crafted or differently-cased Host header to an arbitrary tenant",
    "summary": "Permissive Regular Expression vulnerability in ash-project ash_phoenix lets a remote client select the tenant an Ash application uses, or degrade the request, by sending a crafted Host header. AshPhoenix.Helpers.get_subdomain/2 stripped the root domain with String.replace(host, ~r/.?#{root_host}/, \"\"). The root host was interpolated raw, so each . became a wildcard and any metacharacter a pattern, and the replace was global and unanchored, so a match was removed from anywhere in the string. With root_host example.com, Host: foo.exampleXcom.attacker.net returned the tenant foo.attacker.net. A metacharacter-bearing or nil root host degraded the pattern or raised on every request. The comparison was also case-sensitive, so TENANT.EXAMPLE.COM and EXAMPLE.COM slipped past the root-host allowlist. conn.host comes from the client Host header. The fix matches the root host case-insensitively and only as an exact trailing suffix. This issue affects ash_phoenix: from 2.1.26 before 2.3.25.",
    "evidence": "osv:CVE-2026-82726",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-82726",
      "aliases": [
        "CVE-2026-82726",
        "EEF-CVE-2026-82726",
        "GHSA-rpf8-q9jh-qxrr"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/ash-project/ash_phoenix",
              "type": "GIT",
              "events": [
                {
                  "introduced": "9a5ea4d377bc263de321d79574872a3dfc4fb541"
                },
                {
                  "fixed": "8306f29e77526840c89f3cd244996ce7c0fa2cda"
                },
                {
                  "introduced": "02277a84d03fb43bdcbbb63dd97f9f1727509d8f"
                },
                {
                  "fixed": "1e38e7dc8838426cc94656238d9208759c661c03"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "9a5ea4d377bc263de321d79574872a3dfc4fb541"
                      },
                      {
                        "fixed": "8306f29e77526840c89f3cd244996ce7c0fa2cda"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "introduced": "2.1.26"
                      },
                      {
                        "fixed": "2.3.25"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "fixed": "8306f29e77526840c89f3cd244996ce7c0fa2cda"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v2.3.24",
            "v2.3.23",
            "v2.3.22",
            "v2.3.21",
            "v2.3.20",
            "v2.3.19",
            "v2.3.18",
            "v2.3.17",
            "v2.3.10",
            "v2.3.16",
            "v2.3.15",
            "v2.3.14",
            "v2.3.13",
            "v2.3.12",
            "v2.3.11",
            "v2.3.9",
            "v2.3.8",
            "v2.3.7",
            "v2.3.6",
            "v2.3.5",
            "v2.3.4",
            "v2.3.3",
            "v2.3.2",
            "v2.3.1",
            "v2.3.0",
            "v2.2.0",
            "v2.1.26"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-82726.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:45.786380805Z",
      "provider": "osv",
      "references": [
        "https://cna.erlef.org/cves/CVE-2026-82726.html",
        "https://github.com",
        "https://osv.dev/vulnerability/EEF-CVE-2026-82726",
        "https://repo.hex.pm",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/82xxx/CVE-2026-82726.json",
        "https://github.com/ash-project/ash_phoenix/security/advisories/GHSA-rpf8-q9jh-qxrr",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-82726",
        "https://github.com/ash-project/ash_phoenix/commit/8306f29e77526840c89f3cd244996ce7c0fa2cda",
        "https://github.com/ash-project/ash_phoenix"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-178",
          "CWE-625"
        ],
        "cna_assigner": "EEF",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/82xxx/CVE-2026-82726.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-82726",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 513782,
  "published_at": "2026-08-31T03:05:38.612+00:00"
}