Vulnerability Database

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Total vulnerabilities in the database

Better Auth: OAuth callback accepts mismatched `state` when cookie-backed state storage is used without PKCE — better-auth

Improper Authentication

Am I affected?

Users are affected if all of the following are true:

  • The application uses better-auth at a version below 1.6.2 (or @better-auth/sso paired with such a version).
  • betterAuth({ account: { storeStateStrategy } }) is set to "cookie". The default "database" is not affected.
  • The application wires at least one OAuth provider through genericOAuth({ config }) with pkce: false, or it supplies a custom getToken or tokenUrl that does not require the stored codeVerifier. Stock social providers with PKCE on are not affected.
  • The provider returns arbitrary code values to the configured callback URL.

If users are on [email protected] or later, they are not affected.

Fix:

  1. Upgrade to [email protected] or later (current stable is 1.6.10).
  2. If users cannot upgrade, see workarounds below.

Summary

In parseGenericState, the cookie branch decrypted the oauth_state cookie and validated expiry, but did not compare the incoming OAuth state query parameter to the nonce that generateGenericState issued at sign-in. Any callback to /api/auth/oauth2/callback/<providerId> that arrived with a forged state and any code was therefore accepted as long as the browser still held a live oauth_state cookie. With pkce: false (or any getToken path that does not enforce a code-verifier round-trip), an attacker who forced the victim to deliver an attacker-controlled authorization code to the callback would mint a session bound to the attacker's external identity in the victim's browser. Account-linking flows behaved the same way, binding the attacker's external account to an authenticated victim row.

Details

The cookie branch of parseGenericState did not compare the cookie's stored nonce to the incoming state parameter. The database branch (the default) was not affected because the verification row is keyed by state and the lookup itself enforces equality.

The fix re-binds the cookie to the nonce: generateGenericState writes oauthState: state into the encrypted payload before storage, and parseGenericState rejects when parsedData.oauthState !== state. The same primitive covers every caller (generic-oauth, social, account-link, oauth-proxy passthrough, OIDC SSO, SAML relay state).

Patches

Fixed in [email protected] via PR #8949 (commit 9deb7936a, merged 2026-04-09). The cookie branch of parseGenericState now rejects when the encrypted payload's nonce does not match the incoming state parameter; the database branch gained a defense-in-depth equality check.

Workarounds

If users cannot upgrade immediately:

  • Switch storeStateStrategy back to "database" (the default). This closes the cookie-only bypass without a code change.
  • Enable pkce: true on every affected genericOAuth provider. The codeVerifier is the missing primitive that the attacker cannot supply.

Impact

  • Forced-login (CSRF on OAuth callback): the attacker forces the victim's browser into an authenticated session bound to the attacker's external identity, allowing the attacker to observe the victim's actions inside the application.
  • Persistent account linking: account-link flows bind the attacker's external account to the victim's authenticated row, granting persistent access until the link is removed.

Credit

Reported by @Jvr2022 via private advisory disclosure, and by @alavesa (PatchPilots audit) via the public duplicate issue #8897.

Resources

  • Published: May 15, 2026
  • Updated: Jun 5, 2026
  • GHSA: GHSA-wxw3-q3m9-c3jr
  • Severity: Medium
  • Exploit:
  • CISA KEV:

CVSS v3:

  • Severity: Medium
  • Score: 5.3
  • AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

CWEs:

OWASP TOP 10:

Software From Fixed in
Node.js icon better-auth - 1.6.2

Frequently Asked Questions

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

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