Better Auth @better-auth/sso before 1.7.3 Authentication Bypass via Personal SSO Providers

{
  "id": "2b87b1a32e9f631983bd432c864dc7c4feb3e6c4fa15d38d9cf0ce3240890faf",
  "url": "https://osv.dev/vulnerability/CVE-2026-110863",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Better Auth @better-auth/sso before 1.7.3 Authentication Bypass via Personal SSO Providers",
    "summary": "Better Auth @better-auth/sso from 1.7.0-rc.2 before 1.7.3 contains an authentication bypass vulnerability that allows authenticated users to sign in as other users by registering a personal SSO provider. Attackers can copy a legitimate provider's OIDC issuer or SAML entity ID and assert a victim's subject or NameID, because account lookup ignores providerId, creating sessions for victim accounts.",
    "evidence": "osv:CVE-2026-110863",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-110863",
      "aliases": [
        "CVE-2026-110863",
        "GHSA-mx9r-x6ww-qjw9"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/better-auth/better-auth",
              "type": "GIT",
              "events": [
                {
                  "introduced": "cc708e51bcb1d4c367d2bc6182e6fd7fd722ece8"
                },
                {
                  "fixed": "597d39cb4aaaac1ad729051fbdd22a63b8ba8d8d"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "1.7.0-rc.2"
                      },
                      {
                        "fixed": "1.7.3"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  },
                  {
                    "range": [
                      {
                        "introduced": "1.7.0-rc.2"
                      },
                      {
                        "fixed": "1.7.3"
                      }
                    ],
                    "source": "DESCRIPTION"
                  }
                ]
              }
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-110863.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:37.726874191Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/110xxx/CVE-2026-110863.json",
        "https://github.com/better-auth/better-auth/security/advisories/GHSA-mx9r-x6ww-qjw9",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-110863",
        "https://www.vulncheck.com/advisories/better-auth-better-auth-sso-before-1.7.3-authentication-bypass-via-personal-sso-providers"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-287"
        ],
        "cna_assigner": "VulnCheck",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/110xxx/CVE-2026-110863.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-110863",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 505307,
  "published_at": "2026-10-14T22:52:50.378+00:00"
}