CVE-2026-120814: MultiUpdateCoordinator state replay lets a shard administrator create a persistent cluster root user

An improper privilege management issue in the sharding subsystem of MongoDB Server may allow a user holding certain shard-level administrative privileges to cause persisted internal coordination state to be reprocessed with elevated internal authority. Because that state is trusted rather than re-validated, operations may be carried out beyond the user's authorized scope, including changes to cluster-wide security configuration. Successful triggering this issue requires an authenticated session directly against a cluster member and can result in unauthorized access to and modification of data across the cluster.