Detect Scheduled Batch Exfiltration of Compressed Archive Staging in Google Chronicle

Double-extortion ransomware affiliates routinely stage stolen data into password-protected, multi-volume compressed archives before transferring it off-network, and increasingly schedule that transfer to run in a single batch during off-hours or maintenance windows to minimise the chance of SOC observation and to blend with legitimate scheduled backup jobs. LockBit and BlackCat/ALPHV affiliates have been documented staging data with commands such as `rar.exe a -v500m -hp<password>` (password-protected, 500MB split volumes) and then invoking a transfer tool (rclone, MEGAcmd, curl/SFTP) via a Scheduled Task created specifically for the operation, timed to run during low-traffic overnight hours. Cl0p's mass-exploitation campaigns (e.g., the 2023 MOVEit Transfer exploitation) similarly relied on automated, scripted batch retrieval of staged data at scale rather than interactive, ad hoc transfers, timing collection to minimise operational footprint. This detection targets the composite chain rather than any single step in isolation: (1) an archive utility creating multiple password-protected, size-limited volumes — the staging signature; (2) a Scheduled Task created around the same time, referencing either the archive path/extension or a known transfer tool — the scheduling signature; and (3) network egress from the same host at the scheduled time to a known exfiltration-capable destination. Correlating all three within a short window is a much higher-fidelity indicator of T1029 Scheduled Transfer than any one signal alone, since each individual step (archiving, task scheduling, network egress) has abundant legitimate uses on its own.