Vulnerability-Lookup

CVE-2026-53516 (GCVE-0-2026-53516)

Vulnerability from cvelistv5 – Published: 2026-07-15 17:13 – Updated: 2026-07-15 17:52

Title

Better Auth: Account takeover via OAuth auto-link to unverified pre-registered email

Summary

Better Auth is an authentication and authorization library for TypeScript. Prior to 1.6.11, Better Auth's OAuth callback auto-link gate in handleOAuthUserInfo accepts implicit account linking when the OAuth provider asserts email_verified: true without requiring the local user row's emailVerified field to also be true, allowing an attacker who pre-registers a victim email through /sign-up/email to bind the victim's OAuth identity to the attacker's account. The same primitive affects one-tap, and emailAndPassword.requireEmailVerification: true does not mitigate the link-time verification change. This issue is fixed in version 1.6.11.

Severity

8.3 (High)


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

SSVC

Exploitation: none Automatable: no Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-07-15 17:51 UTC

CWE

CWE-287 - Improper Authentication
CWE-345 - Insufficient Verification of Data Authenticity

Assigner

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/better-auth/better-auth/securi…	x_refsource_CONFIRM
https://github.com/better-auth/better-auth/pull/9578	x_refsource_MISC
https://github.com/better-auth/better-auth/commit…	x_refsource_MISC
https://github.com/better-auth/better-auth/releas…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
better-auth	better-auth	Affected: < 1.6.11	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-53516

Vulnerability from fkie_nvd - Published: 2026-07-15 18:16 - Updated: 2026-07-21 14:14

Severity

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

Summary

References

URL	Tags
security-advisories@github.com	https://github.com/better-auth/better-auth/commit/da7e50beee849c59a2ed1ec6b3a38cc6ab9fb563	Patch
security-advisories@github.com	https://github.com/better-auth/better-auth/pull/9578	Issue Tracking, 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-g38m-r43w-p2q7	Mitigation, Vendor Advisory

Impacted products

	Vendor	Product	Version
	better-auth	better_auth	*

JSON

To clipboard

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          "product": "better-auth",
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GHSA-G38M-R43W-P2Q7

Vulnerability from github – Published: 2026-07-07 20:55 – Updated: 2026-07-20 19:23

Summary

Better Auth has an account takeover issue via OAuth auto-link to unverified pre-registered email

Details

Am I affected?

Users are affected if all of the following are true:

Their application uses better-auth at a version < 1.6.11 on the stable line, or any current next pre-release.
emailAndPassword.enabled: true is set in their application's betterAuth({ ... }) configuration.
At least one OAuth or SSO provider is configured (any built-in social provider, or genericOAuth(...), or any provider via @better-auth/sso).
account.accountLinking.disableImplicitLinking is not set to true.
account.accountLinking.enabled is not set to false.

Setting either disableImplicitLinking: true or enabled: false closes the hole at the cost of breaking the standard "add another login method" UX. emailAndPassword.requireEmailVerification: true does not mitigate, because the link-time emailVerified flip promotes the attacker's row to verified, after which the password login becomes usable.

Fix:

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

Summary

The OAuth callback's auto-link gate in handleOAuthUserInfo admits an implicit account link whenever the provider asserts email_verified: true, without requiring the local user row's emailVerified to also be true. An attacker who pre-registers a victim's email through /sign-up/email (which writes a row with emailVerified: false) can have the victim's later OAuth identity bound to the attacker's user row, granting both a password login and the victim's OAuth identity on the same account. This is the pre-account-hijacking class — the same shape as Microsoft "nOAuth" (2023) and the Sign in with Apple JWT flaw (2020).

Details

The auto-link gate validates only the OAuth provider's userInfo.emailVerified claim. The local row's emailVerified field is never read. When no (accountId, providerId) match exists, the user lookup falls back to email, which surfaces any pre-registered row at that email.

A separate post-link step promotes the local emailVerified to true when the provider's claim is true and the local email matches the provider's email. This step is correct for legitimate first-time linking, but combined with the missing local-side check it becomes load-bearing for the takeover: after the link, the attacker's password row is treated as verified, defeating requireEmailVerification: true as a mitigation.

The fix adds the local-side ownership check to the gate: implicit linking now also rejects when dbUser.user.emailVerified is false. The same primitive lives in one-tap and inherits the same fix shape; the SSO domainVerified short-circuit follows separately as a hardening change.

Patches

Fixed in better-auth@1.6.11. Implicit linking now refuses to attach an OAuth identity to a local account whose emailVerified flag is false. The same gate change applies in the one-tap sign-in plugin, which previously had its own simpler linking path. The Google ID-token email_verified claim is also normalized through toBoolean so a string "false" is treated as falsy (some Google responses send the string, which the prior code treated as truthy).

The public surface for the new gate is account.accountLinking.requireLocalEmailVerified, defaulted to true. Applications whose users sign up through OAuth without ever verifying their email locally can opt out with account: { accountLinking: { requireLocalEmailVerified: false } } to retain the legacy permissive behavior. The option is marked @deprecated; the gate at each call site carries a FIXME pointing at the next-minor follow-up that drops the option and makes the check unconditional.

Test fixtures across the admin, oidc-provider, mcp, generic-oauth, last-login-method, and oauth-provider suites now pre-verify created users via a databaseHooks.user.create.before hook (or the disableTestUser opt-in on the oauth-provider RP fixture) so those suites continue to exercise their role and flow logic rather than tripping the new gate.

Workarounds

If developers cannot upgrade their applications immediately:

Disable implicit linking: set account.accountLinking.disableImplicitLinking: true. Forces all linking through the authenticated /link-social endpoint where the user must already be signed in.
Disable linking entirely: set account.accountLinking.enabled: false. Closes the hole but breaks the multi-login-method UX entirely.

emailAndPassword.requireEmailVerification: true alone does not mitigate, because the link-time emailVerified flip promotes the attacker's row to verified.

Impact

Account takeover via pre-account hijacking: the attacker holds a working password login plus the victim's OAuth identity on the same account, granting persistent access.
requireEmailVerification: true bypass: the attacker's password login becomes usable post-link.
Cross-flow reach: every OAuth and SSO sign-in path that calls handleOAuthUserInfo is affected (built-in social providers, generic-oauth, oauth-proxy, SSO OIDC, SSO SAML, one-tap).

Credit

Reported by @avrmeduard.

Resources

Severity

8.3 (High)


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

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "better-auth"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.6.11"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-53516"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-287",
      "CWE-345"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-07-07T20:55:13Z",
    "nvd_published_at": "2026-07-15T18:16:47Z",
    "severity": "HIGH"
  },
  "details": "### Am I affected?\n\nUsers are affected if all of the following are true:\n\n- Their application uses `better-auth` at a version `\u003c 1.6.11` on the stable line, or any current `next` pre-release.\n- `emailAndPassword.enabled: true` is set in their application\u0027s `betterAuth({ ... })` configuration.\n- At least one OAuth or SSO provider is configured (any built-in social provider, or `genericOAuth(...)`, or any provider via `@better-auth/sso`).\n- `account.accountLinking.disableImplicitLinking` is not set to `true`.\n- `account.accountLinking.enabled` is not set to `false`.\n\nSetting either `disableImplicitLinking: true` or `enabled: false` closes the hole at the cost of breaking the standard \"add another login method\" UX. `emailAndPassword.requireEmailVerification: true` does not mitigate, because the link-time `emailVerified` flip promotes the attacker\u0027s row to verified, after which the password login becomes usable.\n\nFix:\n\n1. Upgrade to `better-auth@1.6.11` or later.\n2. If developers cannot upgrade, see workarounds below.\n\n### Summary\n\nThe OAuth callback\u0027s auto-link gate in `handleOAuthUserInfo` admits an implicit account link whenever the provider asserts `email_verified: true`, without requiring the local user row\u0027s `emailVerified` to also be `true`. An attacker who pre-registers a victim\u0027s email through `/sign-up/email` (which writes a row with `emailVerified: false`) can have the victim\u0027s later OAuth identity bound to the attacker\u0027s user row, granting both a password login and the victim\u0027s OAuth identity on the same account. This is the pre-account-hijacking class \u2014 the same shape as Microsoft \"nOAuth\" (2023) and the Sign in with Apple JWT flaw (2020).\n\n### Details\n\nThe auto-link gate validates only the OAuth provider\u0027s `userInfo.emailVerified` claim. The local row\u0027s `emailVerified` field is never read. When no `(accountId, providerId)` match exists, the user lookup falls back to email, which surfaces any pre-registered row at that email.\n\nA separate post-link step promotes the local `emailVerified` to `true` when the provider\u0027s claim is `true` and the local email matches the provider\u0027s email. This step is correct for legitimate first-time linking, but combined with the missing local-side check it becomes load-bearing for the takeover: after the link, the attacker\u0027s password row is treated as verified, defeating `requireEmailVerification: true` as a mitigation.\n\nThe fix adds the local-side ownership check to the gate: implicit linking now also rejects when `dbUser.user.emailVerified` is `false`. The same primitive lives in `one-tap` and inherits the same fix shape; the SSO `domainVerified` short-circuit follows separately as a hardening change.\n\n### Patches\n\nFixed in `better-auth@1.6.11`. Implicit linking now refuses to attach an OAuth identity to a local account whose `emailVerified` flag is `false`. The same gate change applies in the `one-tap` sign-in plugin, which previously had its own simpler linking path. The Google ID-token `email_verified` claim is also normalized through `toBoolean` so a string `\"false\"` is treated as falsy (some Google responses send the string, which the prior code treated as truthy).\n\nThe public surface for the new gate is `account.accountLinking.requireLocalEmailVerified`, defaulted to `true`. Applications whose users sign up through OAuth without ever verifying their email locally can opt out with `account: { accountLinking: { requireLocalEmailVerified: false } }` to retain the legacy permissive behavior. The option is marked `@deprecated`; the gate at each call site carries a `FIXME` pointing at the next-minor follow-up that drops the option and makes the check unconditional.\n\nTest fixtures across the `admin`, `oidc-provider`, `mcp`, `generic-oauth`, `last-login-method`, and `oauth-provider` suites now pre-verify created users via a `databaseHooks.user.create.before` hook (or the `disableTestUser` opt-in on the oauth-provider RP fixture) so those suites continue to exercise their role and flow logic rather than tripping the new gate.\n\n### Workarounds\n\nIf developers cannot upgrade their applications immediately:\n\n- **Disable implicit linking**: set `account.accountLinking.disableImplicitLinking: true`. Forces all linking through the authenticated `/link-social` endpoint where the user must already be signed in.\n- **Disable linking entirely**: set `account.accountLinking.enabled: false`. Closes the hole but breaks the multi-login-method UX entirely.\n\n`emailAndPassword.requireEmailVerification: true` alone does not mitigate, because the link-time `emailVerified` flip promotes the attacker\u0027s row to verified.\n\n### Impact\n\n- **Account takeover via pre-account hijacking**: the attacker holds a working password login plus the victim\u0027s OAuth identity on the same account, granting persistent access.\n- **`requireEmailVerification: true` bypass**: the attacker\u0027s password login becomes usable post-link.\n- **Cross-flow reach**: every OAuth and SSO sign-in path that calls `handleOAuthUserInfo` is affected (built-in social providers, generic-oauth, oauth-proxy, SSO OIDC, SSO SAML, one-tap).\n\n### Credit\n\nReported by @avrmeduard.\n\n### Resources\n\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- [Sudhodanan \u0026 Paverd, Pre-hijacked accounts: an empirical study of security failures in user account creation on the web (USENIX Security 2022)](https://www.usenix.org/conference/usenixsecurity22/presentation/sudhodanan)",
  "id": "GHSA-g38m-r43w-p2q7",
  "modified": "2026-07-20T19:23:06Z",
  "published": "2026-07-07T20:55:13Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/better-auth/better-auth/security/advisories/GHSA-g38m-r43w-p2q7"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-53516"
    },
    {
      "type": "WEB",
      "url": "https://github.com/better-auth/better-auth/pull/9578"
    },
    {
      "type": "WEB",
      "url": "https://github.com/better-auth/better-auth/commit/da7e50beee849c59a2ed1ec6b3a38cc6ab9fb563"
    },
    {
      "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:R/S:U/C:H/I:H/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Better Auth has an account takeover issue via OAuth auto-link to unverified pre-registered email"
}

Sightings

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Nomenclature

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Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

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.
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Action not permitted

CVE-2026-53516 (GCVE-0-2026-53516)

FKIE_CVE-2026-53516

GHSA-G38M-R43W-P2Q7

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