npm · better-auth
Better Auth vulnerable to unauthorized invitation acceptance via unverified email match in organization plugin
Users are affected if all of the following are true:
better-auth with the organization plugin (import { organization } from "better-auth/plugins/organization").emailAndPassword: { enabled: true } without requireEmailVerification: true.requireEmailVerificationOnInvitation: true on the organization() options.invitationId. Examples: admin UI surfacing the link, copy-paste into chat, forwarded email, mail-forwarding rules at the recipient's domain, link previews logging the URL, or a custom sendInvitationEmail integration that sends to a non-owner channel.If their application set emailAndPassword: { enabled: true, requireEmailVerification: true } so unverified rows cannot reach a usable session, they are not affected. Setting requireEmailVerificationOnInvitation: true closes acceptInvitation and rejectInvitation, but getInvitation and listUserInvitations remain ungated even with that flag.
Fix:
better-auth@1.6.11 or later.The organization plugin's acceptInvitation endpoint trusts an email-string equality check as proof that the session user owns the invited address. With Better Auth's stock emailAndPassword: { enabled: true } configuration, requireEmailVerification defaults to false, so an attacker can sign up a row keyed to victim@target.example (auto-signed-in, emailVerified: false) before the legitimate owner. When an organization admin invites that address, the attacker presents the invitationId and accepts the invitation, joining the organization at the invited role.
The recipient gate compares invitation.email.toLowerCase() to session.user.email.toLowerCase() and returns 403 on mismatch. The opt-in requireEmailVerificationOnInvitation flag adds an emailVerified check, but it defaults to false and only fires on acceptInvitation and rejectInvitation; getInvitation and listUserInvitations have no emailVerified gate at all.
The bearer token (invitationId) is by default 32 chars over [a-zA-Z0-9] (~190 bits), so the realistic attack vector is leakage of the invitation link rather than brute force.
The fix shape defaults the emailVerified gate to on and extends it across all four invitation endpoints (acceptInvitation, rejectInvitation, getInvitation, listUserInvitations). This is the same trust-primitive class as GHSA-g38m-r43w-p2q7 (OAuth auto-link); both ship the rule "email equality is not ownership proof; both sides must prove ownership".
Fixed in better-auth@1.6.11. All four invitation recipient endpoints (acceptInvitation, rejectInvitation, getInvitation, listUserInvitations) now require the session user's emailVerified to be true in addition to the email-string match. The requireEmailVerificationOnInvitation option default flips from false to true, so applications are secure out of the box.
getInvitation and listUserInvitations use the new EMAIL_VERIFICATION_REQUIRED_FOR_INVITATION error code so the wording matches the operation; acceptInvitation and rejectInvitation keep the existing EMAIL_VERIFICATION_REQUIRED_BEFORE_ACCEPTING_OR_REJECTING_INVITATION code. Server-side calls to listUserInvitations that pass ctx.query.email without an authenticated session continue to bypass the gate; the gate is specific to session-authenticated recipient calls.
Integrators who intentionally accept invitations on unverified sessions can preserve the legacy permissive behavior with organization({ requireEmailVerificationOnInvitation: false }). 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. Operators that take this opt-out should understand the takeover risk before doing so.
If developers cannot upgrade their applications immediately:
organization({ requireEmailVerificationOnInvitation: true }). Closes acceptInvitation and rejectInvitation against unverified sessions. Does not close getInvitation or listUserInvitations.emailAndPassword.requireEmailVerification: true (or remove email/password sign-up entirely). Closes the pre-registration step itself.session.user.emailVerified === true and rejects otherwise.invitationId, joins the organization as a member at the invited role.Reported by @widavies.
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Check my repoSources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.