Service account network logon to a device it has not used in 30 days
Builds a per-account baseline of the devices that each enabled service account has made a successful network logon to over the previous 30 days, then alerts when one makes a successful network logon to a device outside that baseline within the latest window. Service accounts are identified from IdentityInfo using each account’s most recent recorded type and enabled status, and are matched to logon events by their on-premises SID, so local accounts or accounts in other domains that share the same name are not mistaken for them. Accounts with no logon history in the baseline period are still evaluated, so a dormant service account that suddenly begins making network logons will alert on every device it reaches. Service accounts tend to touch a small, fixed set of hosts, so a per-entity first-seen check is a strong lateral movement signal with less noise than the same logic applied to users. Each result is enriched with the number of times the destination device’s sensor reporting restarted during the alert window, along with the times of those restarts in UTC, as restarts close to the new logons often indicate maintenance activity such as patching, although they should prompt a check to confirm rather than closure of the alert. The rule runs every 24 hours, as this is the only Defender custom detection frequency with a 30-day lookback, and the alert window covers the last 25 hours so that a slightly delayed run does not leave a gap. The baseline and alert windows are separated by ingestion time rather than event time, so events that arrive late are still evaluated.
Microsoft Sentinel (KQL)
