{
  "affected": [
    {
      "affectedData": [
        {
          "product": "better-auth",
          "vendor": "better-auth",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.6.11"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Better Auth is an authentication and authorization library for TypeScript. Prior to 1.6.11, the legacy oidcProvider and mcp plugins expose OAuth token endpoints whose refresh_token grant authenticates only possession of the bound refreshToken row and matching client_id, without verifying the confidential client\u0027s client_secret, allowing an attacker with a valid refresh_token to mint access tokens and rotated refresh tokens through /api/auth/oauth2/token or /api/auth/mcp/token. The @better-auth/oauth-provider package is not affected. This issue is fixed in version 1.6.11."
    }
  ],
  "id": "CVE-2026-53512",
  "lastModified": "2026-07-15T20:29:17.680",
  "metrics": {
    "cvssMetricV40": [
      {
        "cvssData": {
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "attackComplexity": "LOW",
          "attackRequirements": "PRESENT",
          "attackVector": "NETWORK",
          "availabilityRequirement": "NOT_DEFINED",
          "baseScore": 9.1,
          "baseSeverity": "CRITICAL",
          "confidentialityRequirement": "NOT_DEFINED",
          "exploitMaturity": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "privilegesRequired": "NONE",
          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
          "vulnAvailabilityImpact": "NONE",
          "vulnConfidentialityImpact": "HIGH",
          "vulnIntegrityImpact": "HIGH",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-07-15T18:16:47.420",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/better-auth/better-auth/commit/1f2ff4215c4affff0b140b0c0a712c0dde35659c"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/better-auth/better-auth/pull/9576"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/better-auth/better-auth/releases/tag/v1.6.11"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/better-auth/better-auth/security/advisories/GHSA-pw9m-5jxm-xr6h"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Undergoing Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-287"
        },
        {
          "lang": "en",
          "value": "CWE-306"
        },
        {
          "lang": "en",
          "value": "CWE-345"
        },
        {
          "lang": "en",
          "value": "CWE-863"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "better-auth"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.6.11"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-53512"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-287",
      "CWE-306",
      "CWE-345",
      "CWE-863"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-07T20:11:50Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "### Am I affected?\n\nUsers are affected if all of the following are true:\n\n- Their application uses `better-auth` and has enabled at least one of: `oidcProvider()` (imported from `better-auth/plugins/oidc-provider`), or `mcp()` (imported from `better-auth/plugins/mcp`).\n- Their application has at least one confidential OAuth client registered (any client with `type: \"web\" | \"native\" | \"user-agent-based\"` in the `oauthApplication` table, or any `trustedClients` entry without `type: \"public\"`). Public clients with PKCE are not affected.\n- Their application uses `better-auth` at a version below the patched release.\n\nIf an application only uses `@better-auth/oauth-provider` (the canonical replacement for `oidc-provider`) and the `mcp` plugin is not enabled, it is not affected.\n\nFix:\n\n1. Upgrade to `better-auth@1.6.11` or later.\n2. Migrate from the deprecated `oidcProvider()` to `@better-auth/oauth-provider` when feasible. The new package enforces client authentication on both grants by default.\n3. If developers cannot upgrade their applications, see workarounds below.\n\n### Summary\n\nThe legacy `oidcProvider` and `mcp` plugins each expose an OAuth 2.0 token endpoint whose `refresh_token` grant authenticates the request entirely on possession of the bound `refreshToken` row and a matching `client_id`. Neither plugin verifies the registered confidential client\u0027s `client_secret` on the refresh path. An attacker who obtains any valid `refresh_token` (via database read, log capture, browser-side XSS, or CORS-amplified script in the mcp case) and the public `client_id` can mint fresh access tokens and rotated refresh tokens until the chain is revoked.\n\n### Details\n\nRFC 6749 \u00a76 and OAuth 2.1 \u00a74.3 require confidential clients to authenticate to the token endpoint on every grant, including refresh. The same plugins\u0027 `authorization_code` grant correctly enforces `client_secret` (the oidc-provider via `verifyStoredClientSecret`, the mcp plugin via raw equality), which proves the omission on the refresh path is a regression rather than a design choice.\n\nToken rotation issues a new `refresh_token` with each call, so a single leaked refresh-token grants indefinite access until the row is revoked or its `refreshTokenExpiresAt` (default 7 days) passes; rotation refreshes that window each call.\n\nTwo adjacent issues on the mcp surface ship in the same patch. The mcp `authorization_code` grant uses raw `===` for client-secret comparison and ignores the `storeClientSecret: \"encrypted\" | \"hashed\"` configuration; the fix routes both grants through `verifyStoredClientSecret`. The mcp `/mcp/token` endpoint sets `Access-Control-Allow-Origin: *` unconditionally, which amplifies the refresh bypass in browser contexts; the fix narrows the CORS allowlist.\n\nThe newer `@better-auth/oauth-provider` package routes both grants through `validateClientCredentials` and is not affected.\n\n### Patches\n\nFixed in `better-auth@1.6.11`. The legacy `oidcProvider` and `mcp` token endpoints now require `client_secret` on the `refresh_token` grant for confidential clients, using the same constant-time comparison the `authorization_code` grant already used. Public clients are unaffected (they have no secret to enforce, and PKCE substitutes on the auth-code grant).\n\nThe `Authorization: Basic` parser is fixed to follow RFC 6749 \u00a72.3.1: the credential is split on the first colon and each half is percent-decoded. Client IDs and secrets that contain reserved characters now authenticate correctly. The `/mcp/token` endpoint\u0027s CORS configuration is narrowed in the same change (the wildcard `Access-Control-Allow-Origin: *` header is removed), matching the standalone `@better-auth/oauth-provider` package.\n\nThe deprecated `oidc-provider` plugin remains deprecated. The recommended migration path is `@better-auth/oauth-provider`.\n\n### Workarounds\n\nNone of these close the bug fully without a code patch.\n\n- **Migrate to `@better-auth/oauth-provider`** if your deployment can adopt the new plugin. It enforces `client_secret` on both grants.\n- **Force all clients to public + PKCE**: set every client\u0027s `type: \"public\"` and require PKCE. The bug is unreachable when there is no `client_secret` to verify.\n- **Network-layer ingress restriction**: limit `/api/auth/oauth2/token` and `/api/auth/mcp/token` to known client IPs at the load balancer. Practical for server-to-server flows, not for end-user-device clients.\n- **Out-of-band refresh-token rotation**: on any suspicion of leak, run `db.deleteMany({ model: \"oauthAccessToken\", where: [{ field: \"clientId\", value: \u003cid\u003e }] })` to invalidate all refresh tokens for the affected client.\n- **For the mcp endpoint specifically**: drop the wildcard CORS at an upstream proxy and replace with a tight allowlist.\n\n### Impact\n\n- **Indefinite confidential-client impersonation**: an attacker holding any valid `refresh_token` and the public `client_id` can mint access tokens and rotated refresh tokens indefinitely, until the row is revoked. Rotation refreshes the expiration window each call.\n- **Resource access at the user\u0027s authorized scope**: every minted access token carries the original user\u0027s authorization scope, so the attacker reads or writes whatever the resource server grants for that scope.\n\n### Credit\n\nReported by @subhanUmer.\n\n### Resources\n\n- [CWE-306: Missing Authentication for Critical Function](https://cwe.mitre.org/data/definitions/306.html)\n- [CWE-287: Improper Authentication](https://cwe.mitre.org/data/definitions/287.html)\n- [CWE-345: Insufficient Verification of Data Authenticity](https://cwe.mitre.org/data/definitions/345.html)\n- [CWE-863: Incorrect Authorization](https://cwe.mitre.org/data/definitions/863.html)\n- [RFC 6749 \u00a76: Refreshing an Access Token](https://datatracker.ietf.org/doc/html/rfc6749#section-6)\n- [OAuth 2.1 \u00a74.3: Refresh Token](https://datatracker.ietf.org/doc/html/draft-ietf-oauth-v2-1#section-4.3)",
  "id": "GHSA-pw9m-5jxm-xr6h",
  "modified": "2026-07-07T20:11:50Z",
  "published": "2026-07-07T20:11:50Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/better-auth/better-auth/security/advisories/GHSA-pw9m-5jxm-xr6h"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/better-auth/better-auth"
    },
    {
      "type": "WEB",
      "url": "https://github.com/better-auth/better-auth/releases/tag/v1.6.11"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Better Auth: OAuth refresh-token replay via missing client authentication on oidc-provider and mcp plugins"
}