ZITADEL: Cross-Tenant User Leakage via Recycled Identifiers

Summary

A flaw in the user lifecycle enforcement allowed deleted users to retain their original organization/tenant association. Recreating a deleted user under a distinct organization can cause the new user instance to be incorrectly provisioned within the original organization if the previous ID would be used to recreate it.

Impact

When a user is created, the system maps the generated or provided ID to its target organization (Org A). When that user is subsequently deleted, a deletion event is appended to the stream, but the historical mapping of the resource owner within the event store's validation layer is not cleared.

If a new user is later provisioned in a different organization (Org B) using that exact same ID, the event store validation logic reads the stream's history, matches it to the original organization, and routes the new user's events to Org A instead of Org B.

This issue represents a localized multi-tenancy isolation anomaly rather than an easily exploitable attack vector. Because the new user instance is incorrectly routed and provisioned inside Org A instead of Org B, an administrator from Org A inadvertently gains full access to this new user record.

However, there is no technical mechanism for a malicious actor to force, automate, or target this behavior against a specific user or tenant. Because the scenario relies entirely on an accidental sequence of operational events and requires the recycling of a highly specific ID space, the practical security risk is exceptionally low.

Affected Versions

Systems running one of the following versions are affected:

• 4.x: 4.0.0 through 4.15.1 (including RC versions)
• 3.x: 3.0.0 through 3.4.11 (including RC versions)

Patches

The vulnerability has been addressed in the latest releases. The patch resolves the issue by requiring the correct permission in case the verification flag is provided and only allows self-management of the email address, resp. phone number itself.

• 4.x: Upgrade to $\ge$4.15.2
• 3.x: Update to $\ge$4.15.2

Workarounds

The recommended solution is to upgrade to a patched version.