A cross-tenant issue is a security flaw that allows data, actions, or permissions to cross the boundary between separate customer tenants in a shared cloud service. In a multitenant SaaS platform, each tenant should remain logically isolated, even though many customers use the same underlying infrastructure.
This matters because tenant boundaries are part of the trust model. If an attacker can trigger a cross-tenant path through identity checks, authorization logic, connectors, or misconfiguration, they may read another customer’s data, act on their resources, or disrupt their workflows. Defenders look for strong tenant isolation, strict allowlists, and explicit checks on every request so that one customer’s tokens, sessions, and integrations cannot be reused across environments.