Detect File Transfer Protocols in CrowdStrike LogScale
Adversaries may communicate using application layer protocols associated with transferring files to avoid detection/network filtering by blending in with existing traffic. Commands to the remote system, and often the results of those commands, will be embedded within the protocol traffic between the client and server. Protocols such as SMB, FTP, FTPS, and TFTP that transfer files may be very common in environments. Packets produced from these protocols may have many fields and headers in which data can be concealed. Data could also be concealed within the transferred files. An adversary may abuse these protocols to communicate with systems under their control within a victim network while also mimicking normal, expected traffic.
MITRE ATT&CK
- Tactic
- Command and Control
- Technique
- T1071 Application Layer Protocol
- Sub-technique
- T1071.002 File Transfer Protocols
- Canonical reference
- https://attack.mitre.org/techniques/T1071/002/
LogScale Detection Query
#event_simpleName = NetworkConnectIP4
| RemotePort in (20, 21, 69, 139, 445, 990)
// Drop RFC1918, loopback, and APIPA destinations
| RemoteAddressIP4 != /^10\./
| RemoteAddressIP4 != /^172\.(1[6-9]|2[0-9]|3[01])\./
| RemoteAddressIP4 != /^192\.168\./
| RemoteAddressIP4 != /^127\./
| RemoteAddressIP4 != /^169\.254\./
| TransferProtocol := case {
RemotePort in (20, 21, 990) => "FTP/FTPS";
RemotePort in (445, 139) => "SMB";
RemotePort = 69 => "TFTP";
* => "Unknown"
}
// Aggregate per host + process + remote endpoint
| groupBy(
[ComputerName, ImageFileName, UserName, RemoteAddressIP4, RemotePort, TransferProtocol],
function=[
count(as=ConnectionCount),
sum(BytesSent, as=TotalBytesSent),
sum(BytesReceived, as=TotalBytesReceived),
min(@timestamp, as=FirstSeen),
max(@timestamp, as=LastSeen)
]
)
| ConnectionCount > 3
| ExfilRisk := case {
TotalBytesSent > 10485760 => "HIGH";
TotalBytesSent > 1048576 => "MEDIUM";
* => "LOW"
}
| sort(ConnectionCount, order=desc)CrowdStrike Falcon LogScale (CQL) query over NetworkConnectIP4 sensor events to identify processes on an endpoint making more than 3 outbound connections to public IP addresses on file transfer protocol ports (FTP 20/21/990, SMB 445/139, TFTP 69) within the selected time range. Groups by host, process image path, username, remote IP, and port; aggregates connection count and byte volumes; assigns an exfiltration risk tier. Requires Falcon Insight sensor with network telemetry enabled.
Data Sources
Required Tables
False Positives & Tuning
- Endpoint backup agents (e.g., Veeam Agent, Acronis Cyber Protect) configured to send backups to external FTP/FTPS repositories will generate high ConnectionCount and TotalBytesSent from the backup process executable.
- Development workstations running FTP or SMB clients to sync code repositories or assets with externally hosted servers — especially common in remote developer environments connecting to company-owned cloud VMs with public IPs.
- Security tooling such as vulnerability scanners or EDR management consoles that establish SMB connections to externally reachable managed endpoints during asset scanning or policy push operations.
Other platforms for T1071.002
Testing Methodology
Validate this detection against 3 adversary techniques 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 1FTP C2 Simulation via Built-in Client
Expected signal: Sysmon Event ID 1: Process creation for ftp.exe with -s: flag pointing to script file. Sysmon Event ID 3: Network connection attempt to 127.0.0.1:21. Sysmon Event ID 11: File creation of ftp_c2.txt in TEMP directory.
- Test 2SMB Named Pipe C2 Simulation
Expected signal: Sysmon Event ID 17: Pipe Created with PipeName=\\msagent_f1. Sysmon Event ID 1: PowerShell process creation with named pipe creation in command line. The pipe name 'msagent_f1' is a known Cobalt Strike default pipe name pattern.
- Test 3FTP Data Exfiltration via curl
Expected signal: Sysmon for Linux Event ID 3: Network connection from curl to 127.0.0.1:21. Process creation event for curl with -T (upload) flag and ftp:// URL. File creation event for the test file.
References (6)
- https://attack.mitre.org/techniques/T1071/002/
- https://www.us-cert.gov/ncas/alerts/TA18-074A
- https://www.welivesecurity.com/wp-content/uploads/2019/08/ESET_Machete.pdf
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1071.002/T1071.002.md
- https://thedfirreport.com/2021/08/29/cobalt-strike-a-defenders-guide/
- https://www.mandiant.com/resources/blog/apt41-dual-espionage-and-cyber-crime-operation
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