A flaw was found in migration-planner. The agent-API middleware processes JSON Web Tokens (JWTs) for authentication, but its UpdateSourceInventory and UpdateAgentStatus handlers fail to validate the source id claim within these tokens against the requested source ID. This oversight allows an authenticated attacker with a valid agent token to manipulate data across different tenants, leading to a complete collapse of tenant isolation. This could result in unauthorized overwriting of victim inventory, planting of malicious credential URLs, or corruption of migration assessments.