Vulnerability-Lookup

CVE-2026-53517 (GCVE-0-2026-53517)

Vulnerability from cvelistv5 – Published: 2026-07-15 17:33 – Updated: 2026-07-15 19:21

Title

Better Auth OAuth Provider: Refresh Token Rotation Race Condition Allows Concurrent Replay and Token Family Forking

Summary

Better Auth is an authentication and authorization library for TypeScript. From 1.4.8-beta.7 until 1.6.11, the @better-auth/oauth-provider POST /oauth2/token endpoint on the refresh_token grant performs a non-atomic read, validate, revoke, and mint sequence on the oauthRefreshToken row, allowing concurrent requests with the same parent refresh token to pass the revoked check and create forked refresh-token families; the vulnerable range also includes embedded better-auth plugin versions before 1.6.0. This issue is fixed in version 1.6.11.

Severity

8.1 (High)


                        
                          CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

SSVC

Exploitation: none Automatable: no Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-07-15 19:20 UTC

CWE

CWE-362 - Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')
CWE-367 - Time-of-check Time-of-use (TOCTOU) Race Condition

Assigner

GitHub_M mitre root

References

3 references

URL	Tags
https://github.com/better-auth/better-auth/securi…	x_refsource_CONFIRM
https://github.com/better-auth/better-auth/commit…	x_refsource_MISC
https://github.com/better-auth/better-auth/releas…	x_refsource_MISC

Impacted products

2 products

Vendor	Product	Version	CPE status
better-auth	better-auth	Affected: >= 1.4.8-beta.7, < 1.6.0	guessed
@better-auth	oauth-provider	Affected: >= 1.6.0, < 1.6.11	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-53517

Vulnerability from fkie_nvd - Published: 2026-07-15 18:16 - Updated: 2026-07-21 16:00

Severity

8.1 (High) - CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/better-auth/better-auth/commit/c6918ecc9e3a75892169415d7f6c95b591b6a52d	Patch
security-advisories@github.com	https://github.com/better-auth/better-auth/releases/tag/v1.6.11	Release Notes
security-advisories@github.com	https://github.com/better-auth/better-auth/security/advisories/GHSA-392p-2q2v-4372	Mitigation, Vendor Advisory

Impacted products

Vendor	Product	Version
better-auth	better-auth\/oauth-provider	*
better-auth	better_auth	*
better-auth	better_auth	1.4.8
better-auth	better_auth	1.4.8

JSON

To clipboard

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        "Vendor Advisory"
      ],
      "url": "https://github.com/better-auth/better-auth/security/advisories/GHSA-392p-2q2v-4372"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-362"
        },
        {
          "lang": "en",
          "value": "CWE-367"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-392P-2Q2V-4372

Vulnerability from github – Published: 2026-07-07 20:55 – Updated: 2026-07-20 19:24

Summary

Better Auth: OAuth refresh-token rotation forks the token family on concurrent redemption

Details

Am I affected?

Users are affected if all of the following are true:

Their project depends on @better-auth/oauth-provider at a version >= 1.6.0, < 1.6.11, or uses the embedded plugin in better-auth >= 1.4.8-beta.7, < 1.6.0.
At least one OAuth client served by their application's authorization server requests the offline_access scope, so refresh tokens are minted.
Concurrent redemption of the same refresh token is reachable: an SPA shares one refresh token across browser tabs without a mutex, a mobile client retries after a transient failure, an attacker who has stolen a refresh token times two requests, or a service worker queues offline requests.

If developer applications do not request offline_access for any client, no refresh tokens are minted and they are not exposed.

Fix:

Upgrade to @better-auth/oauth-provider@1.6.11 or later.
If developers cannot upgrade, see workarounds below.

Summary

The OAuth provider's POST /oauth2/token endpoint, on the refresh_token grant, performs a non-atomic read / validate / revoke / mint sequence on the oauthRefreshToken row. Two concurrent requests presenting the same parent refresh token both pass the revocation check before either revoke completes, so each mints a fresh refresh token. The replay-detection branch only fires when revoked is already truthy at read time, which is exactly the state concurrent attackers race past. The result is a forked refresh-token family from a single parent token.

Details

The adapter.update predicate on the parent row is keyed on id only; it does not include revoked IS NULL, so two concurrent updates both succeed (last-write-wins, no error path). The schema does not declare unique on oauthRefreshToken.token, so concurrent creates do not collide on a unique-key violation either.

RFC 9700 §4.14 (OAuth Security Best Current Practice) prescribes refresh-token family invalidation on detected reuse; this implementation tries to enforce that contract through the revoked check, but the check is not atomic with the consumption step. Token rotation issues a new refresh token with each call, so a single stolen refresh token grants indefinite access until the row is revoked or its refreshTokenExpiresAt (default 7 days) passes. Rotation refreshes that window each call.

The fix lands an atomic compare-and-swap on the parent row inside the rotation primitive (UPDATE ... WHERE id = ? AND revoked IS NULL with a rowcount check), so the losing rotation fails closed with invalid_grant and the parent row stays marked revoked. Subsequent replay of the original refresh token then trips the existing family-invalidation guard. The schema gains a unique constraint on oauthRefreshToken.token for parity with oauthAccessToken.token.

Patches

Fixed in @better-auth/oauth-provider@1.6.11. The refresh-token rotation primitive now performs an atomic compare-and-swap on the parent row, and the explicit revokeRefreshToken path uses the same CAS. On a contested rotation, exactly one caller wins and mints a fresh refresh token; the loser receives invalid_grant. Subsequent replay of the original refresh token trips the existing family-invalidation guard because the parent row stays marked revoked.

@better-auth/memory-adapter@1.6.11 ships a compatibility fix in the same wave: the in-memory where clause now treats undefined and null as equivalent under an eq null predicate, mirroring SQL IS NULL and Mongo's missing-or-null semantics. Without this change, the CAS predicate WHERE revoked IS NULL falls through on every call against a row whose optional revoked field is absent (the adapter factory's transformInput skips writing undefined when no default exists), so the rotation above is broken for any deployment using the in-memory adapter.

Strict refresh-token family invalidation on a contested rotation, per RFC 9700 §4.14 (which calls for invalidating the winner's tokens too when reuse is detected at rotation time), is deferred to a follow-up minor on the next channel. Closing it cleanly requires an opt-in transactional rotation in the adapter contract so the family-delete cannot interleave with the winner's in-flight access-token insert. The deferred site carries a FIXME(strict-family-invalidation) marker.

Schema-migration note: the better-auth migration generator only emits UNIQUE for newly-created columns. Existing installs will not pick up the new oauthRefreshToken.token unique constraint from migrate / generate; add it manually if an application's operational tooling depends on it (CREATE UNIQUE INDEX oauth_refresh_token_token_uniq ON "oauthRefreshToken" (token);). The CAS fix above does not depend on the database-level constraint to be correct; the constraint is defense-in-depth so collisions from a buggy custom generateRefreshToken callback fail loudly.

Workarounds

None of these close the bug fully without a code patch.

Adapter-level: configure the database adapter to run the OAuth refresh handler under serializable isolation, or wrap the adapter.update on oauthRefreshToken with a row-level pessimistic lock (SELECT ... FOR UPDATE). Narrows the window without closing it.
Token lifetime: pass oauthProvider({ refreshTokenExpiresIn: 60 }) to expire forked families within one minute. Trades attacker persistence for shorter user sessions.
Client-side single-flight: serialize refresh-token usage in the client SDK with a mutex. Mitigates honest concurrency but does nothing against an attacker with a stolen refresh token.
Disable refresh tokens: do not request the offline_access scope. Closes the surface but breaks long-lived sessions.

Impact

Indefinite access from a single stolen refresh token: forked refresh-token families grant access at the original user's authorization scope, surviving past any single revocation if an attacker holds any branch.
Detection bypass: legitimate users whose refresh token has been forked do not trip family invalidation when they refresh, because the attacker's branch already swapped the parent row out from under the legitimate user's check.

Credit

Reported by @chdanielmueller.

Resources

Severity

8.1 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

7.6 (High)


                  
                    CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Show details on source website

JSON

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "@better-auth/oauth-provider"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.6.0"
            },
            {
              "fixed": "1.6.11"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "npm",
        "name": "better-auth"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.4.8-beta.7"
            },
            {
              "fixed": "1.6.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-53517"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-294",
      "CWE-362",
      "CWE-367",
      "CWE-613"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-07T20:55:48Z",
    "nvd_published_at": "2026-07-15T18:16:48Z",
    "severity": "HIGH"
  },
  "details": "### Am I affected?\n\nUsers are affected if all of the following are true:\n\n- Their project depends on `@better-auth/oauth-provider` at a version `\u003e= 1.6.0, \u003c 1.6.11`, or uses the embedded plugin in `better-auth \u003e= 1.4.8-beta.7, \u003c 1.6.0`.\n- At least one OAuth client served by their application\u0027s authorization server requests the `offline_access` scope, so refresh tokens are minted.\n- Concurrent redemption of the same refresh token is reachable: an SPA shares one refresh token across browser tabs without a mutex, a mobile client retries after a transient failure, an attacker who has stolen a refresh token times two requests, or a service worker queues offline requests.\n\nIf developer applications do not request `offline_access` for any client, no refresh tokens are minted and they are not exposed.\n\nFix:\n\n1. Upgrade to `@better-auth/oauth-provider@1.6.11` or later.\n2. If developers cannot upgrade, see workarounds below.\n\n### Summary\n\nThe OAuth provider\u0027s `POST /oauth2/token` endpoint, on the `refresh_token` grant, performs a non-atomic read / validate / revoke / mint sequence on the `oauthRefreshToken` row. Two concurrent requests presenting the same parent refresh token both pass the revocation check before either revoke completes, so each mints a fresh refresh token. The replay-detection branch only fires when `revoked` is already truthy at read time, which is exactly the state concurrent attackers race past. The result is a forked refresh-token family from a single parent token.\n\n### Details\n\nThe `adapter.update` predicate on the parent row is keyed on `id` only; it does not include `revoked IS NULL`, so two concurrent updates both succeed (last-write-wins, no error path). The schema does not declare `unique` on `oauthRefreshToken.token`, so concurrent creates do not collide on a unique-key violation either.\n\nRFC 9700 \u00a74.14 (OAuth Security Best Current Practice) prescribes refresh-token family invalidation on detected reuse; this implementation tries to enforce that contract through the `revoked` check, but the check is not atomic with the consumption step. Token rotation issues a new refresh token with each call, so a single stolen refresh token grants indefinite access until the row is revoked or its `refreshTokenExpiresAt` (default 7 days) passes. Rotation refreshes that window each call.\n\nThe fix lands an atomic compare-and-swap on the parent row inside the rotation primitive (`UPDATE ... WHERE id = ? AND revoked IS NULL` with a rowcount check), so the losing rotation fails closed with `invalid_grant` and the parent row stays marked revoked. Subsequent replay of the original refresh token then trips the existing family-invalidation guard. The schema gains a unique constraint on `oauthRefreshToken.token` for parity with `oauthAccessToken.token`.\n\n### Patches\n\nFixed in `@better-auth/oauth-provider@1.6.11`. The refresh-token rotation primitive now performs an atomic compare-and-swap on the parent row, and the explicit `revokeRefreshToken` path uses the same CAS. On a contested rotation, exactly one caller wins and mints a fresh refresh token; the loser receives `invalid_grant`. Subsequent replay of the original refresh token trips the existing family-invalidation guard because the parent row stays marked revoked.\n\n`@better-auth/memory-adapter@1.6.11` ships a compatibility fix in the same wave: the in-memory `where` clause now treats `undefined` and `null` as equivalent under an `eq null` predicate, mirroring SQL `IS NULL` and Mongo\u0027s missing-or-null semantics. Without this change, the CAS predicate `WHERE revoked IS NULL` falls through on every call against a row whose optional `revoked` field is absent (the adapter factory\u0027s `transformInput` skips writing `undefined` when no default exists), so the rotation above is broken for any deployment using the in-memory adapter.\n\nStrict refresh-token family invalidation on a contested rotation, per RFC 9700 \u00a74.14 (which calls for invalidating the winner\u0027s tokens too when reuse is detected at rotation time), is deferred to a follow-up minor on the `next` channel. Closing it cleanly requires an opt-in transactional rotation in the adapter contract so the family-delete cannot interleave with the winner\u0027s in-flight access-token insert. The deferred site carries a `FIXME(strict-family-invalidation)` marker.\n\nSchema-migration note: the better-auth migration generator only emits `UNIQUE` for newly-created columns. Existing installs will not pick up the new `oauthRefreshToken.token` unique constraint from `migrate` / `generate`; add it manually if an application\u0027s operational tooling depends on it (`CREATE UNIQUE INDEX oauth_refresh_token_token_uniq ON \"oauthRefreshToken\" (token);`). The CAS fix above does not depend on the database-level constraint to be correct; the constraint is defense-in-depth so collisions from a buggy custom `generateRefreshToken` callback fail loudly.\n\n### Workarounds\n\nNone of these close the bug fully without a code patch.\n\n- **Adapter-level**: configure the database adapter to run the OAuth refresh handler under serializable isolation, or wrap the `adapter.update` on `oauthRefreshToken` with a row-level pessimistic lock (`SELECT ... FOR UPDATE`). Narrows the window without closing it.\n- **Token lifetime**: pass `oauthProvider({ refreshTokenExpiresIn: 60 })` to expire forked families within one minute. Trades attacker persistence for shorter user sessions.\n- **Client-side single-flight**: serialize refresh-token usage in the client SDK with a mutex. Mitigates honest concurrency but does nothing against an attacker with a stolen refresh token.\n- **Disable refresh tokens**: do not request the `offline_access` scope. Closes the surface but breaks long-lived sessions.\n\n### Impact\n\n- **Indefinite access from a single stolen refresh token**: forked refresh-token families grant access at the original user\u0027s authorization scope, surviving past any single revocation if an attacker holds any branch.\n- **Detection bypass**: legitimate users whose refresh token has been forked do not trip family invalidation when they refresh, because the attacker\u0027s branch already swapped the parent row out from under the legitimate user\u0027s check.\n\n### Credit\n\nReported by @chdanielmueller.\n\n### Resources\n\n- [CWE-362: Concurrent Execution using Shared Resource with Improper Synchronization (Race Condition)](https://cwe.mitre.org/data/definitions/362.html)\n- [CWE-367: Time-of-check Time-of-use (TOCTOU) Race Condition](https://cwe.mitre.org/data/definitions/367.html)\n- [CWE-294: Authentication Bypass by Capture-replay](https://cwe.mitre.org/data/definitions/294.html)\n- [CWE-613: Insufficient Session Expiration](https://cwe.mitre.org/data/definitions/613.html)\n- [RFC 9700 \u00a74.14: Refresh Token Protection](https://datatracker.ietf.org/doc/html/rfc9700#section-4.14)\n- [RFC 6749 \u00a76: Refreshing an Access Token](https://datatracker.ietf.org/doc/html/rfc6749#section-6)",
  "id": "GHSA-392p-2q2v-4372",
  "modified": "2026-07-20T19:24:47Z",
  "published": "2026-07-07T20:55:48Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/better-auth/better-auth/security/advisories/GHSA-392p-2q2v-4372"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-53517"
    },
    {
      "type": "WEB",
      "url": "https://github.com/better-auth/better-auth/commit/c6918ecc9e3a75892169415d7f6c95b591b6a52d"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/better-auth/better-auth"
    },
    {
      "type": "WEB",
      "url": "https://github.com/better-auth/better-auth/releases/tag/v1.6.0"
    },
    {
      "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:L/UI:N/S:U/C:H/I:H/A:N",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Better Auth: OAuth refresh-token rotation forks the token family on concurrent redemption"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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Action not permitted

CVE-2026-53517 (GCVE-0-2026-53517)

FKIE_CVE-2026-53517

GHSA-392P-2Q2V-4372

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