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Response snapshot Oct 27, 2026, 16:01 UTC

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VulnerabilityGHSA-r4xp-prcw-77qf

better-auth: OAuth Proxy lets an attacker sign in as another user

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.

Published Updated

At a glance

Exploited
Not known
Severity
Not scored yet
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: better-auth: 1.7.7. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-r4xp-prcw-77qf (opens a new tab)

What happened

## 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.

Continue reading

## 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.

Affected package ranges reported by GitHub: better-auth: >= 1.5.0-beta.12, < 1.7.7

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-r4xp-prcw-77qf (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-r4xp-prcw-77qf, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 27). better-auth: OAuth Proxy lets an attacker sign in as another user. https://kevwire.com/record/GHSA-r4xp-prcw-77qf

MLA

"better-auth: OAuth Proxy lets an attacker sign in as another user." KEVWire, 27 Oct. 2026, kevwire.com/record/GHSA-r4xp-prcw-77qf.

Chicago

KEVWire. "better-auth: OAuth Proxy lets an attacker sign in as another user." Last modified October 27, 2026. https://kevwire.com/record/GHSA-r4xp-prcw-77qf.

Evidence summary (plain text)

better-auth: OAuth Proxy lets an attacker sign in as another user (Oct 27, 2026).
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).
Sources:
GitHub-reviewed advisory GHSA-r4xp-prcw-77qf: https://github.com/advisories/GHSA-r4xp-prcw-77qf
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: GHSA-r4xp-prcw-77qf.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 16:00 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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