Description

NextAuth.js provides authentication for Next.js. Prior to@auth/core 0.41.3 and next-auth 4.24.15 and 5.0.0-beta.32, Auth.js stores the OAuth/OIDC anti-CSRF checks state, nonce, and the PKCE verifier in global cookies that are not bound to the provider that created them. On callback, a check value minted during a sign-in started with one provider can satisfy the callback for a different provider because the stored cookie is not verified against the callback provider's identity, including the provider ID, issuer, client ID, or redirect URI. In a multi-provider application that permits account linking while logged in, when one provider's authorization request is observable and a target provider callback can be satisfied without a PKCE verifier, an attacker can lure a victim into starting a legitimate same-origin flow and link the attacker's target-provider account to the victim's Auth.js user. The linked provider grants the attacker persistent sign-in to the victim's account, while cross-site request forgery alone is insufficient. This issue is fixed in @auth/core 0.41.3 and next-auth 4.24.15 and 5.0.0-beta.32.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "6.8",
  "pubDate": "2026-08-12T21:17:41.033Z",
  "pubdate": "2026-08-12T21:17:41.033Z",
  "executiveSummary": "A cross-site request forgery and state confusion vulnerability exists in NextAuth.js and @auth/core where OAuth and OIDC anti-CSRF check states, nonces, and PKCE verifiers are stored in global cookies that lack binding to the specific authentication provider that generated them.\nThe vulnerability impacts multi-provider applications that permit account linking while a user is already authenticated. An attacker can manipulate authentication flows to link an attacker-controlled target-provider account to a victim's user profile.\nSuccessful exploitation allows an attacker to gain persistent unauthorized sign-in access to the victim's account via the linked provider. The attack requires the victim to be lured into starting a legitimate same-origin authentication flow, an observable authorization request from one provider, and a target provider callback that can be satisfied without a PKCE verifier.\nThe issue is resolved in @auth/core version 0.41.3, next-auth version 4.24.15, and next-auth version 5.0.0-beta.32.",
  "technicalDetails": "The root cause of the vulnerability lies in the state management mechanism of Auth.js, where anti-CSRF checks state, nonces, and PKCE verifiers are maintained in global cookies rather than being cryptographically or structurally bound to the specific identity of the provider that initiated the authentication sequence.\nDuring the authentication callback phase, check values minted during a sign-in flow initiated with one provider can successfully satisfy the callback validation for an entirely different provider. The stored cookie values are not validated against the callback provider's unique identity parameters, which include the provider ID, issuer, client ID, or redirect URI.\nIn a multi-provider application configuration that supports account linking while a user is actively logged in, the attack flow proceeds when an attacker observes or triggers an authorization request from an initial provider.\nThe attacker leverages the decoupled nature of the global cookies to substitute or cross-use validation parameters, targeting a different provider whose callback can be processed without enforcing a strict PKCE verifier.\nBy luring the victim into initiating a legitimate same-origin sign-in flow, the attacker forces the application to accept validation tokens or states across provider boundaries.\nThis behavior results in the malicious linking of the attacker's target-provider account to the victim's legitimate Auth.js user session.\nFollowing successful account linking, the attacker achieves post-exploitation persistence, utilizing the linked external provider to persistently access and control the victim's account.\nThe vulnerable components are managed within @auth/core prior to version 0.41.3, next-auth prior to version 4.24.15, and next-auth prior to version 5.0.0-beta.32."
}