What is S7 Comm?
S7 Comm (also known as the Siemens S7 Communication Protocol) is a proprietary communication protocol used for data exchange between Siemens PLCs, HMIs, SCADA systems, and other automation components in industrial environments.
S7 Comm forms the core of many Siemens-based OT infrastructures, particularly in manufacturing, water management, chemicals, and energy.
🧠 Characteristics of S7 Comm
| Characteristic | Description |
|---|---|
| Vendor-specific | Developed exclusively by Siemens |
| Runs over TCP/IP | Standard via port 102 (RFC 1006) |
| Unencrypted | No encryption, no authentication in classic implementations |
| Memory access | Direct access to data bits, memory addresses, and registers of the PLC |
| No standard user management | Authentication usually only at HMI/SCADA level, not at protocol level |
📦 Application in OT
| Use case | Example |
|---|---|
| Data acquisition | SCADA reads process data (temperature, flow, status bits) from the PLC |
| Remote control | Operator panel or SCADA sends setpoints or switches actuators |
| Diagnostics | Reading PLC status, error codes, or firmware version |
| Firmware/configuration updates | Upload/download via TIA Portal or engineering station |
🔐 Cybersecurity risks
| Vulnerability | Description |
|---|---|
| No encryption or authentication | All traffic is readable and manipulable using tools such as Wireshark or Snap7 |
| Susceptible to Replay Attacks | Commands can easily be replayed |
| Misuse via standard tools | Public tools (Snap7, s7comm_decode) can be used for exploits |
| No user identity | The protocol does not distinguish users → no RBAC possible |
| Man-In-The-Middle possible | Traffic can be modified without detection |
🔧 Security measures for S7 Comm
| Measure | Recommendation |
|---|---|
| Segmentation via VLAN/firewall | Allow only trusted traffic to TCP port 102 |
| Protocol whitelisting via Firewall | Permit only specific commands and IP addresses |
| Logging & monitoring | Inspect traffic for S7 patterns using IDS, SIEM |
| Upgrade to S7 Comm Plus / OPC UA | Newer Siemens systems support encrypted communication |
| Jump Server architecture | Engineering stations only within a secured management zone |
| Zero Trust Architecture | Never grant implicit trust within OT segments |
🔁 S7 Comm vs S7 Comm Plus
| Property | S7 Comm (classic) | S7 Comm Plus |
|---|---|---|
| Encryption | ❌ | ✅ (TLS 1.2+) |
| Authentication | ❌ | ✅ (at session level) |
| Port number | TCP/102 | TCP/102 + specific configuration |
| Siemens S7-1500 required | ❌ | ✅ |
| Safe for cloud/coupling | ❌ | ✅ |
📌 In summary
S7 Comm is the backbone of Siemens automation, but also a vulnerable communication protocol. Without security measures it offers attack opportunities for data leakage, sabotage, or unauthorised control.