GHSA-J8V8-G9CX-5QF4

Am I affected?

Users are affected if all of these hold:

• They install and register the @better-auth/scim plugin (plugins: [scim()]).
• They create SCIM providers without an organizationId, that is, non-organization ("personal") providers. Organization-scoped providers are not affected because they enforce organization membership and role.
• Their application's deployment has more than one authenticated user, so one account can target another user's provider.
• They have not set providerOwnership: { enabled: true }.

The SCIM management endpoints first shipped in 1.5.0, so every stable release from 1.5.0 onward is affected, and the stable line is not patched. On the pre-release line, builds through 1.7.0-beta.3 are affected, and 1.7.0-beta.4 carries the fix.

Fix:

1. Upgrade to @better-auth/[email protected] (then 1.7.0). This is a breaking change: it removes the providerOwnership option, makes owner binding mandatory, and adds a permanent scimProvider.userId column.
2. Run the schema migration after upgrading (npx auth migrate). Connections created before the upgrade carry no owner and become unreachable through the management endpoints, so reclaim them at the database level.
3. The 1.6.x stable line is not patched. If developers stay on it, apply the workaround below.

@better-auth/scim does not bind non-organization SCIM providers to their creator in the default configuration. Any authenticated user can manage another user's non-org provider, including reading its metadata, listing connections, regenerating its SCIM bearer token, and deleting the connection. Regenerating the token rotates it: the legitimate token stops working and the attacker holds a valid one.

Details

The plugin tracks provider ownership through an opt-in providerOwnership option and a scimProvider.userId column. Both default to off. When ownership is disabled, a non-org provider row is created without a userId, and the management access check denies access only when a stored owner id is present and differs from the caller:

// non-organization branch of the access check
} else if (provider.userId && provider.userId !== userId) {
  throw new APIError("FORBIDDEN", { message: "You must be the owner to access this provider" });
}

Because the default row has no userId, the condition is false and the request is allowed. The same gap reaches every management operation: token generation and regeneration, single-provider read, the connection list (which returns providers where p.userId === userId || !p.userId), and provider deletion.

The most sensitive operation is token regeneration. If Alice creates a non-org provider corp-idp, Bob can call the same generate-token endpoint with providerId: "corp-idp". The existing row passes the ownerless access check, so the plugin deletes it, creates a fresh row, and returns a new SCIM bearer token to Bob. Alice's previous token is now invalid, and Bob's token authenticates against that provider's SCIM API routes.

This requires no organization membership and no elevated role. It is reachable in the default scim() configuration whenever non-organization providers are used.

Proof of concept

Two authenticated users, Alice and Bob, in a default scim() setup:

1. Alice signs in and creates a non-org provider: POST /scim/generate-token with { "providerId": "corp-idp" }.
2. Bob signs in and reads Alice's provider: GET /scim/get-provider-connection?providerId=corp-idp returns 200 with { "providerId": "corp-idp" }.
3. Bob regenerates the token: POST /scim/generate-token with { "providerId": "corp-idp" } returns 201 and a new scimToken.
4. Alice's old token is rejected at GET /scim/v2/Users (401); Bob's regenerated token is accepted (200).

The behavior is reproducible through Better Auth's public API surface with two distinct sessions.

Workarounds

Until a patched version is available:

• Set providerOwnership: { enabled: true } when registering the plugin, then run the schema update so the scimProvider.userId column exists (npx auth generate or npx auth migrate). New non-org providers are then owner-bound and non-owners are denied. Providers created before enabling ownership stay ownerless until recreated.
• Or scope every SCIM provider to an organization by always passing organizationId. Organization providers enforce membership and role and are not exposed.
• Or restrict access to the SCIM management endpoints at the edge while non-org providers remain ownerless.

Credit

Reported by Jvr2022 through a private GitHub Security Advisory.

Resources

• CWE-862 Missing Authorization: https://cwe.mitre.org/data/definitions/862.html
• CWE-639 Authorization Bypass Through User-Controlled Key: https://cwe.mitre.org/data/definitions/639.html
• SCIM 2.0 Protocol (RFC 7644): https://datatracker.ietf.org/doc/html/rfc7644
• OAuth 2.0 Bearer Token Usage (RFC 6750): https://datatracker.ietf.org/doc/html/rfc6750