Detect File Transfer Protocols in Elastic Security
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/
Elastic Detection Query
network where event.type in ("connection", "start") and
event.outcome == "success" and
network.direction in ("outbound", "egress") and
destination.port in (20, 21, 69, 139, 445, 990) and
not cidrmatch(destination.ip, "10.0.0.0/8", "172.16.0.0/12", "192.168.0.0/16", "127.0.0.0/8", "::1/128", "169.254.0.0/16", "fe80::/10")
/* Deploy as Elastic Threshold Rule:
Threshold: count > 3
Group by: host.name, process.executable, destination.ip, destination.port
Time window: 24h
This base EQL filters candidate events; the threshold config enforces the >3 count */Detects repeated outbound connections on file transfer protocol ports (FTP port 20/21, FTPS port 990, SMB ports 445/139, TFTP port 69) to public IP addresses. Deployed as a threshold rule with count > 3 grouped by host, process, destination IP, and destination port to surface sustained transfer activity indicative of C2 or exfiltration via T1071.002. Uses Elastic Common Schema (ECS) network fields from Endpoint Security or Packetbeat.
Data Sources
Required Tables
False Positives & Tuning
- IT administrators or DevOps engineers using FTP/SFTP to deploy content to externally hosted web servers or CDNs — common in organisations without a central deployment pipeline.
- Scheduled backup agents (e.g., Veeam, Acronis, rsync over FTP) replicating data to external storage providers will generate high connection counts with large BytesSent values.
- Windows domain controllers or file servers with legitimate external SMB traffic to cloud-based file shares (e.g., Azure Files via port 445) will fire when destination IP resolves to a Microsoft public range.
- Pentest or red team engagements using FTP/SMB as a deliberate living-off-the-land transfer mechanism during an authorised assessment.
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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