Detect Application Layer Protocol in Splunk
Adversaries may communicate using OSI application layer protocols 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. Adversaries may utilize many different protocols, including those used for web browsing, transferring files, electronic mail, DNS, or publishing/subscribing. For connections that occur internally within an enclave (such as those between a proxy or pivot node and other nodes), commonly used protocols are SMB, SSH, or RDP.
MITRE ATT&CK
- Tactic
- Command and Control
- Technique
- T1071 Application Layer Protocol
- Canonical reference
- https://attack.mitre.org/techniques/T1071/
SPL Detection Query
index=proxy OR index=firewall OR index=network sourcetype IN ("stream:tcp", "pan:traffic", "cisco:asa", "squid")
dest_port IN (80, 443, 53, 21, 25, 110, 143, 8080, 8443, 1883, 5222)
action=allowed
NOT (dest_ip="10.*" OR dest_ip="172.16.*" OR dest_ip="192.168.*" OR dest_ip="127.*")
| bin _time span=5m
| stats count as ConnectionCount, dc(dest_ip) as UniqueDestIPs, dc(dest_port) as UniquePorts, values(dest_port) as Ports, earliest(_time) as FirstSeen, latest(_time) as LastSeen by src_ip, process_name
| where ConnectionCount > 10
| eval Duration=LastSeen-FirstSeen
| eval AvgInterval=if(ConnectionCount>1, Duration/(ConnectionCount-1), 0)
| where AvgInterval > 1 AND AvgInterval < 3600
| eval BeaconScore=case(
(AvgInterval >= 55 AND AvgInterval <= 65) OR (AvgInterval >= 295 AND AvgInterval <= 305), "high",
1=1, "medium")
| table FirstSeen, LastSeen, src_ip, process_name, ConnectionCount, UniqueDestIPs, Ports, AvgInterval, BeaconScore
| sort - ConnectionCountDetects potential C2 beaconing across application layer protocols by analyzing outbound connection patterns from proxy, firewall, or network stream logs. Groups connections into 5-minute windows and calculates the average interval between connections to identify periodic callback patterns. Common C2 frameworks like Cobalt Strike, Sliver, and Mythic beacon at regular intervals over HTTP, DNS, FTP, or pub/sub protocols.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Legitimate software performing periodic update checks (Windows Update, antivirus definitions, NTP)
- Monitoring and heartbeat agents that maintain persistent connections to cloud management platforms
- Chat and collaboration applications (Slack, Teams, Zoom) with long-lived WebSocket or polling connections
- IoT devices communicating via MQTT to cloud brokers on regular intervals
Other platforms for T1071
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 1Multi-Protocol Beaconing Simulation
Expected signal: Sysmon for Linux Event ID 3 (Network Connection) showing curl processes connecting to 127.0.0.1 on ports 80, 443, 53. Firewall logs showing outbound connection attempts.
- Test 2IRC C2 Channel Simulation
Expected signal: Sysmon Event ID 3: Network Connection to port 6667 (IRC). Process creation event for nc/netcat with IRC protocol commands in arguments.
- Test 3HTTP Beaconing with Cobalt Strike User-Agent
Expected signal: Sysmon Event ID 3: Network Connection from powershell.exe to 127.0.0.1:80. Proxy logs showing repeated requests to /pixel.gif with suspicious User-Agent. Sysmon Event ID 1: PowerShell process creation for each iteration.
References (6)
- https://attack.mitre.org/techniques/T1071/
- https://arxiv.org/ftp/arxiv/papers/1408/1408.1136.pdf
- https://www.mandiant.com/resources/blog/unc3524-eye-spy-email
- https://learn.microsoft.com/en-us/defender-endpoint/advanced-hunting-devicenetworkevents-table
- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1071/T1071.md
- https://github.com/SigmaHQ/sigma/tree/master/rules/network
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