Detect File Transfer Protocols in Microsoft Sentinel
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/
KQL Detection Query
let TimeWindow = 24h;
// Detect anomalous FTP/SMB/TFTP connections to external IPs
DeviceNetworkEvents
| where Timestamp > ago(TimeWindow)
| where RemotePort in (20, 21, 445, 139, 69, 990)
| where RemoteIPType == "Public"
| where ActionType == "ConnectionSuccess"
| summarize
ConnectionCount = count(),
BytesSent = sum(SentBytes),
BytesReceived = sum(ReceivedBytes),
FirstSeen = min(Timestamp),
LastSeen = max(Timestamp)
by DeviceName, InitiatingProcessFileName, RemoteIP, RemotePort, AccountName
| extend Protocol = case(
RemotePort in (20, 21, 990), "FTP/FTPS",
RemotePort in (445, 139), "SMB",
RemotePort == 69, "TFTP",
"Unknown")
| where ConnectionCount > 3
| project LastSeen, DeviceName, AccountName, InitiatingProcessFileName, RemoteIP, RemotePort, Protocol, ConnectionCount, BytesSent, BytesReceived, FirstSeen
| sort by ConnectionCount descDetects outbound connections to public IPs on file transfer protocol ports (FTP 20/21, FTPS 990, SMB 445/139, TFTP 69). Outbound FTP and SMB connections to the internet are highly unusual in most enterprise environments and are strong indicators of C2 or data exfiltration. Known malware families using FTP C2 include Machete, PoetRAT, Kazuar, ShadowPad, and ZxShell. SMB-based C2 is used by Cobalt Strike, Havoc, and Mythic.
Data Sources
Required Tables
False Positives & Tuning
- Legitimate FTP file transfers to external vendors or partner organizations (common in manufacturing, healthcare, and finance)
- SFTP/FTPS connections to cloud-hosted file exchange platforms (e.g., GoAnywhere, MOVEit)
- SMB connections through VPN tunnels to remote offices that appear as public IPs before NAT
- Automated backup scripts that upload to external FTP servers
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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