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2.3 KiB
S7comm Protocol Security Analysis - API Reference
pyshark Library
Python wrapper for TShark (Wireshark CLI) for packet analysis.
Loading S7comm Traffic
import pyshark
cap = pyshark.FileCapture("traffic.pcap", display_filter="s7comm")
for pkt in cap:
s7_layer = pkt.s7comm
print(s7_layer.rosctr, s7_layer.param_func)
cap.close()
Key S7comm Layer Fields
| Field | Description |
|---|---|
s7comm.rosctr |
PDU type: 1=Job, 2=Ack, 3=Ack-Data, 7=Userdata |
s7comm.param_func |
Function code (hex) |
s7comm.error_class |
Error class (0 = no error) |
s7comm.error_code |
Specific error code |
s7comm.param_data |
Parameter data payload |
S7comm Function Codes
| Code | Name | Risk Level |
|---|---|---|
| 0x04 | Read Var | Low - read process data |
| 0x05 | Write Var | High - modify PLC memory |
| 0x28 | Setup Communication | Low - session init |
| 0x29 | PLC Run | Critical - start PLC execution |
| 0x1a | PLC Stop | Critical - halt PLC execution |
| 0xf0 | Userdata | Medium - diagnostics/programming |
S7comm Protocol Overview
S7comm runs over ISO-on-TCP (RFC 1006) on port 102. The protocol stack:
- TCP connection on port 102
- TPKT header (RFC 1006)
- COTP connection-oriented transport (ISO 8073)
- S7comm PDU
Security Concerns
- No built-in authentication in S7comm (pre-S7comm-Plus)
- No encryption of traffic
- Write operations can modify PLC logic and process values
- Stop/Run commands can halt industrial processes
Detection Patterns
Unauthorized Access
Multiple unique source IPs connecting to a single PLC (> 3 sources) indicates potential unauthorized access.
Brute Force
Repeated error responses (error_class != 0) from a PLC to a single source exceeding threshold count.
Dangerous Operations
Any write_var, run, or stop function codes should be flagged and correlated with authorized change windows.
Output Schema
{
"report": "s7comm_protocol_security_analysis",
"total_s7_packets": 1500,
"total_findings": 8,
"severity_summary": {"critical": 2, "high": 5, "medium": 1},
"traffic_patterns": {"function_distribution": {"read_var": 1200, "write_var": 50}},
"findings": [{"type": "dangerous_operation_stop", "severity": "critical"}]
}
CLI Usage
python agent.py --pcap capture.pcap --brute-threshold 10 --output report.json