GHSA-fmh4-wcc4-5jm3 is a high-severity (CVSS 7.7) Improper Authentication vulnerability in better-auth. O3 Security confirms whether GHSA-fmh4-wcc4-5jm3 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Better Auth vulnerable to unauthorized invitation acceptance via unverified email match in organization plugin
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-fmh4-wcc4-5jm3.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-fmh4-wcc4-5jm3 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 0 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
better-authnpmDescription
Am I affected?
Users are affected if all of the following are true:
- Their application uses
better-authwith theorganizationplugin (import { organization } from "better-auth/plugins/organization"). - Their application enables a sign-up surface that allows arbitrary unverified email registration. Most commonly
emailAndPassword: { enabled: true }withoutrequireEmailVerification: true. - Their application has not set
requireEmailVerificationOnInvitation: trueon theorganization()options. - Their application invitation distribution flow allows anyone other than the invited mailbox owner to obtain the
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 customsendInvitationEmailintegration 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:
- Upgrade to
[email protected]or later. - If developers cannot upgrade their application, see workarounds below.
Summary
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 [email protected] (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.
Details
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".
Patches
Fixed in [email protected]. 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.
Workarounds
If developers cannot upgrade their applications immediately:
- Set
organization({ requireEmailVerificationOnInvitation: true }). ClosesacceptInvitationandrejectInvitationagainst unverified sessions. Does not closegetInvitationorlistUserInvitations. - Set
emailAndPassword.requireEmailVerification: true(or remove email/password sign-up entirely). Closes the pre-registration step itself. - Layer middleware on the organization invitation routes that asserts
session.user.emailVerified === trueand rejects otherwise.
Impact
- Account takeover via pre-account hijacking on the org invitation surface: the attacker, holding only an unverified self-issued session and the leaked
invitationId, joins the organization as a member at the invited role. - Organization membership reach: the attacker reads invitation contents and any organization-scoped data the joined role can see, and acts as a member of the victim organization.
Credit
Reported by @widavies.
Resources
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | better-auth | all versions | 1.6.11 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for better-auth. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update better-auth to 1.6.11 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-fmh4-wcc4-5jm3 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-fmh4-wcc4-5jm3 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-fmh4-wcc4-5jm3. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-fmh4-wcc4-5jm3 in your dependencies?
O3 detects GHSA-fmh4-wcc4-5jm3 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.