Mastra versions up to 1.63.0 perform an authentication bypass in the memory API thread ownership validation when the mapUserToResourceId callback is omitted from the configuration. The ownership check is effectively a no‑op in this scenario, allowing an authenticated user to list and read any thread owned by other users. This capability can expose conversation history and metadata belonging to different resource owners, potentially leaking confidential business or personal information.

The affected product is Mastra AI’s Mastra platform. Any deployment of Mastra version 1.63.0 or earlier where mapUserToResourceId is not set in the configuration is vulnerable. Versions newer than 1.63.0 are presumed not to exhibit this flaw.

The vulnerability scores a 7.1 CVSS, indicating significant impact and a high likelihood of exploitation if an attacker can authenticate. The EPSS score is not available, so the current exploitation probability cannot be quantified, but the flaw is present in a production API used by authenticated users, making exploitation feasible. The vulnerability is not listed in the CISA KEV catalog. Authenticated attackers can enumerate all threads via GET /api/memory/threads and read data that should be restricted to the owning resource. The attack vector is likely through legitimate API calls, requiring valid credentials but not elevated privileges beyond those normally granted to a logged‑in user.