Network
Serial Terminal Server
A device converting serial links to TCP so legacy equipment becomes network reachable.
High criticalityLevel 2 – Level 1
What it does
Tunnels serial protocols such as Modbus RTU over IP networks.
Typically locatedPanels containing legacy serial devices.
At a glance
PurdueLevel 2 – Level 1
CategoryNetwork
Protocolsmodbus-rtu, modbus-tcp, iec-60870-5-101
Talks toLegacy controllers, SCADA / polling servers
Common vendorsMoxa, Digi, Lantronix
Why should I care?
Serial Terminal Server sits at Level 2 – Level 1. Compromise here is not just a data problem — it changes what the physical process does or what operators can see and control.
Common security problems
- Legacy web management with default credentials
- Makes previously isolated serial devices remotely reachable
- Often forgotten in inventories
If it is compromised
- Remote reach to devices that assumed physical isolation
What to monitor
- Management access
- Client IPs connecting to serial ports
- Firmware versions
How to defend it
- Change default credentials and disable unused management
- Restrict client IPs
- Inventory every terminal server
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