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Complete skill folder anatomy across all cybersecurity skills: - scripts/agent.py: 80-150 line Python agents using real libraries (impacket, boto3, azure-mgmt-*, kubernetes, pefile, yara, scapy, shodan, stix2, etc.) - references/api-reference.md: real API documentation with method signatures - LICENSE: MIT license for all skill folders
1.6 KiB
1.6 KiB
API Reference: Detecting Modbus Protocol Anomalies
Modbus Protocol Limits
| Parameter | Maximum Value |
|---|---|
| Coil read quantity | 2000 |
| Register read quantity | 125 |
| Register write quantity | 123 |
| Unit ID range | 1-247 |
| PDU size | 253 bytes |
Anomaly Detection Methods
| Anomaly | Detection | Severity |
|---|---|---|
| Timing deviation | Polling interval outside tolerance | MEDIUM-HIGH |
| Excessive read | Quantity > protocol limits | HIGH |
| Invalid function code | Not in standard set | HIGH |
| Modbus scan | >5 unique function codes from source | HIGH |
| Register range violation | Address outside configured range | MEDIUM |
Zeek Modbus Log Fields
#fields ts uid id.orig_h id.orig_p id.resp_h id.resp_p func exception quantity
Suricata Modbus Rules
alert modbus any any -> any 502 (msg:"Modbus Invalid Function Code"; \
modbus: function !1,!2,!3,!4,!5,!6,!15,!16; sid:4000001;)
alert modbus any any -> any 502 (msg:"Modbus Excessive Register Read"; \
modbus: function 3; modbus: quantity > 125; sid:4000002;)
Scapy Modbus Analysis
from scapy.contrib.modbus import ModbusADURequest
from scapy.all import rdpcap
pkts = rdpcap("modbus.pcap")
for pkt in pkts:
if pkt.haslayer(ModbusADURequest):
print(f"FC={pkt.funcCode} Len={pkt.len}")
Baseline Monitoring
# Expected polling behavior
expected_interval = 1.0 # seconds
tolerance = 0.5
# Alert if interval < 0.5s or > 3.0s
CLI Usage
python agent.py --modbus-log modbus.log
python agent.py --modbus-log modbus.log --expected-interval 2.0