ash_authentication_oauth2_server CIMD fetcher classifies IPv4-in-IPv6 and site-local addresses as public, allowing SSRF

{
  "id": "3cd0b6a2671305e065f0fcc6ac73957a93a22707c3e0dadacf8a79ded8b32c6e",
  "url": "https://osv.dev/vulnerability/CVE-2026-82757",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "ash_authentication_oauth2_server CIMD fetcher classifies IPv4-in-IPv6 and site-local addresses as public, allowing SSRF",
    "summary": "Server-Side Request Forgery (SSRF) vulnerability in ash-project ash_authentication_oauth2_server allows an attacker who controls a client metadata URL and its DNS to make the server connect to internal or loopback addresses. public_ip?/1 in AshAuthentication.Oauth2Server.CIMD.ReqFetcher enforces the outbound policy for CIMD metadata fetches. It classified several address forms as publicly routable that are not: IPv4-compatible ::/96 (for example ::127.0.0.1), SIIT IPv4-translated ::ffff:0:0:0/96, and deprecated site-local fec0::/10. A returned AAAA record in one of these ranges passed the policy, so a fetch pinned to that address reached space the policy was meant to block. This issue affects ash_authentication_oauth2_server: from 0.3.0 before 0.3.1.",
    "evidence": "osv:CVE-2026-82757",
    "products": [],
    "severity": "medium",
    "structured": {
      "id": "CVE-2026-82757",
      "aliases": [
        "CVE-2026-82757",
        "EEF-CVE-2026-82757",
        "GHSA-wprp-8gvj-p6cv"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/ash-project/ash_authentication_oauth2_server",
              "type": "GIT",
              "events": [
                {
                  "introduced": "e713a9ba816761140c226e2ca55b75c0b93f5984"
                },
                {
                  "fixed": "268b591261a3473ab9b87272963e4dd2fd99d972"
                },
                {
                  "introduced": "2681877faf2ef0df7d95852c2a72e9e972c64b7e"
                },
                {
                  "fixed": "15bde4311e31c925a428f34c02b283307619e2a2"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "e713a9ba816761140c226e2ca55b75c0b93f5984"
                      },
                      {
                        "fixed": "268b591261a3473ab9b87272963e4dd2fd99d972"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "introduced": "0.3.0"
                      },
                      {
                        "fixed": "0.3.1"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "fixed": "268b591261a3473ab9b87272963e4dd2fd99d972"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v0.3.0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-82757.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:37.412094852Z",
      "provider": "osv",
      "references": [
        "https://cna.erlef.org/cves/CVE-2026-82757.html",
        "https://github.com",
        "https://osv.dev/vulnerability/EEF-CVE-2026-82757",
        "https://repo.hex.pm",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/82xxx/CVE-2026-82757.json",
        "https://github.com/ash-project/ash_authentication_oauth2_server/security/advisories/GHSA-wprp-8gvj-p6cv",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-82757",
        "https://github.com/ash-project/ash_authentication_oauth2_server/commit/268b591261a3473ab9b87272963e4dd2fd99d972",
        "https://github.com/ash-project/ash_authentication_oauth2_server"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-918"
        ],
        "cna_assigner": "EEF",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/82xxx/CVE-2026-82757.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-82757",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 504808,
  "published_at": "2026-09-07T22:31:34.656+00:00"
}