Detection Strategy for Exfiltration Over Web Service

ID: DET0548
Domains: Enterprise
Analytics: AN1511, AN1512, AN1513, AN1514, AN1515
Version: 1.0
Created: 21 October 2025
Last Modified: 21 October 2025

Analytics

AN1511

Processes that normally do not initiate network communications suddenly making outbound HTTPS connections with high outbound-to-inbound data ratios. Defender view: correlation between process creation logs (e.g., Word, Excel, PowerShell) and subsequent anomalous network traffic volumes toward common web services (Dropbox, Google Drive, OneDrive).

Log Sources
Data Component Name Channel
Process Creation (DC0032) WinEventLog:Security EventCode=4688
Network Connection Creation (DC0082) WinEventLog:Sysmon EventCode=3
File Creation (DC0039) WinEventLog:Sysmon EventCode=11
Mutable Elements
Field Description
MonitoredServices List of legitimate web services to baseline (Dropbox, OneDrive, Google Drive).
ExfilVolumeThreshold Outbound data threshold for flagging unusual activity, tunable by environment.
TimeWindow Aggregation period to calculate anomalies in outbound data volume.

AN1512

Processes (tar, curl, python scripts) accessing large file sets and initiating outbound HTTPS POST requests with payload sizes inconsistent with baseline activity. Defender perspective: detect abnormal sequence of file archival followed by encrypted uploads to external web services.

Log Sources
Data Component Name Channel
Command Execution (DC0064) auditd:EXECVE curl or wget with POST/PUT options
File Access (DC0055) auditd:SYSCALL open/read of sensitive directories (/etc, /home/*)
Network Traffic Flow (DC0078) NSM:Flow sustained outbound HTTPS sessions with high data volume
Mutable Elements
Field Description
MonitoredTools Suspicious command-line utilities used for exfiltration (curl, wget, python).
DataVolumeThreshold Bytes transferred threshold per session to flag unusual uploads.

AN1513

Office apps or scripts writing files followed by xattr manipulation (to evade quarantine) and subsequent HTTPS uploads. Defender perspective: anomalous file modification + outbound TLS traffic originating from non-networking apps (Word, Excel, Preview).

Log Sources
Data Component Name Channel
Process Creation (DC0032) macos:unifiedlog execution of Office binaries with network activity
File Access (DC0055) macos:unifiedlog read/write of user documents prior to upload
Network Traffic Content (DC0085) macos:unifiedlog outbound TLS connections to cloud storage providers
Mutable Elements
Field Description
WatchedApplications Applications not expected to perform bulk data transfers (Office apps, Preview).

AN1514

Abnormal API calls from user accounts invoking file upload endpoints outside normal baselines (M365, Google Drive, Box). Defender perspective: monitor unified audit logs for elevated frequency of Upload, Create, or Copy operations from compromised accounts.

Log Sources
Data Component Name Channel
Application Log Content (DC0038) m365:unified FileUploaded or FileCopied events
Network Traffic Content (DC0085) saas:box API calls exceeding baseline thresholds
Mutable Elements
Field Description
APICallThreshold Maximum number of API calls per user/session before triggering alert.
UserBaselineProfiles Baseline normal data transfer patterns by user/role.

AN1515

ESXi guest OS or management interface processes establishing unexpected external HTTPS connections. Defender perspective: monitor vmx or hostd processes making outbound web requests with significant data transfer.

Log Sources
Data Component Name Channel
Network Connection Creation (DC0082) esxi:vmkernel network session initiation with external HTTPS services
File Access (DC0055) esxi:hostd file copy or datastore upload via HTTPS
Mutable Elements
Field Description
DatastoreTransferThreshold Threshold for outbound transfers from ESXi datastores.