Better Auth 1.5.0-beta.12 before 1.7.7 Authentication Bypass via OAuth Proxy

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Better Auth from 1.5.0-beta.12 before 1.7.7 contains an authentication bypass vulnerability in the OAuth Proxy plugin that allows unauthenticated attackers to sign in as other users by forging encrypted profiles. When the proxy shares the global secret and cookie-stored state is used, attackers can obtain encrypted state for a fake profile with a victim's verified email to take over the account via implicit linking.

Source published

14 Oct 2026 22:52:51 UTC

Source modified

15 Oct 2026 15:36:16 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 4.0 · 9.1 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

CVSS 3.1 · 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Better Auth from 1.5.0-beta.12 before 1.7.7 contains an authentication bypass vulnerability in the OAuth Proxy plugin that allows unauthenticated attackers to sign in as other users by forging encrypted profiles. When the proxy shares the global secret and cookie-stored state is used, attackers can obtain encrypted state for a fake profile with a victim's verified email to take over the account via implicit linking.

Source published

Oct 14, 2026, 10:52:51 PM (timezone not stated)

Source modified

Oct 15, 2026, 3:36:16 PM (timezone not stated)

Observed here

30 Oct 2026 01:56:03 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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EUVD CVSS 4.0 · 9.1 CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N

Better Auth from 1.5.0-beta.12 before 1.7.7 contains an authentication bypass vulnerability in the OAuth Proxy plugin that allows unauthenticated attackers to sign in as other users by forging encrypted profiles. When the proxy shares the global secret and cookie-stored state is used, attackers can obtain encrypted state for a fake profile with a victim's verified email to take over the account via implicit linking.

Source published

14 Oct 2026 23:17:27 UTC

Source modified

16 Oct 2026 18:25:45 UTC

Observed here

27 Oct 2026 16:45:50 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 9.1 CVSS:4.0/AV:N/AC:H/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

CVSS 3.1 · [email protected] · Secondary · 7.4 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

## Am I affected? You may be affected if you use `better-auth` from 1.5.0-beta.12 through versions before 1.7.7 with the OAuth Proxy plugin. You are affected only if **all** of these are also true: - On a participating environment, the OAuth Proxy plugin has no dedicated `secret`, or its `secret` equals that environment's global Better Auth secret. - Sign-in state is stored in a cookie (`account.storeStateStrategy: "cookie"`). With a database or secondary storage, this is only the case if you chose it explicitly. - Implicit account linking is on (the default). You are not affected by this path if every participating environment uses a proxy `secret` distinct from its global Better Auth secret, if sign-in state is stored in the database, or if you use a version before 1.5.0-beta.12. ## Summary The OAuth Proxy plugin trusts any user profile it can decrypt. In the affected setup, Better Auth encrypts sign-in state, including data the caller chose, with the same secret and hands it to anyone who starts a social sign-in. An attacker can use this to get a fake profile for another user's email address that the proxy accepts as real. ## Impact An attacker without an account who knows a user's verified email address can sign in as that user, with that user's permissions. They can read private data, change the account, and link a provider account of their choice to it. They need no provider sign-in and no action from the victim. No availability impact is established, and a reported open redirect was not confirmed. ## Patches The fix is merged for the planned `better-auth` 1.7.7 release. That package is not available yet. Upgrade all nodes handling the same cookie-backed OAuth or SAML state flow and all OAuth Proxy participants together, including the production coordinator and preview or development deployments. Keep installed Better Auth packages released alongside `better-auth` on the same release version. Restart pending sign-in and account-linking flows; pre-upgrade state cookies and proxy payloads are rejected. Public options and API signatures are unchanged. ## Workarounds Until you upgrade to the fixed release, apply one of these: - Set one strong OAuth Proxy `secret` across every environment that takes part in the proxy flow, and keep it different from each environment's global Better Auth secret. - Set `account.storeStateStrategy: "database"`. This is already the default when a database or secondary storage is configured. If Magic Link is also enabled, switching can expose a separate cross-purpose verification-record path in affected releases. Ensure the two flows resolve to distinct stored identifiers; with built-in options, use Magic Link `storeToken: "hashed"` with global `verification.storeIdentifier` unset or `"plain"`, or disable Magic Link or both built-in social and Generic OAuth sign-in. - Remove the OAuth Proxy plugin if you do not need it. Setting `account.accountLinking.disableImplicitLinking: true` stops this path from taking over an existing account. It does not fix the underlying flaw: the callback can still accept attacker-made data as a provider identity. Apply one of the steps above as well.

Source published

27 Oct 2026 15:32:16 UTC

Source modified

27 Oct 2026 15:47:24 UTC

Observed here

27 Oct 2026 16:44:03 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Publisher rating · HIGH