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" (https://github.com/zitadel/zitadel/releases/tag/v4.15.2) - 3.x: Update to $\ge$"4.15.2" (https://github.com/zitadel/zitadel/releases/tag/v4.15.2) Workarounds The recommended solution is to upgrade to a patched version. Questions If you have any questions or comments about this advisory, please email us at "security@zitadel.com" (mailto:security@zitadel.com) Credits Thanks to Charlie Graven from Famedly for reporting this vulnerability.