Disabling Vulnerable SSL 2.0 and SSL 3.0 Protocols in PCS 7 Environments

In SIMATIC PCS 7 V7.x and V8.x environments, SSL 2.0 and SSL 3.0 cryptographic protocols are cryptographically obsolete and vulnerable to eavesdropping attacks (such as POODLE). They are not used by PCS 7 core automation protocols (S7 communication, ISO Transport, Named Connections, or WinCC internal terminal bus). In accordance with the Siemens Industrial Security Compendium, SSL 2.0 and SSL 3.0 can and should be completely disabled on Engineering Stations, OS Servers, and OS Clients. To disable, set the 'Enabled' DWORD registry values to 0 under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols for both SSL 2.0 and SSL 3.0, uncheck SSL in Internet Options, and enforce TLS 1.2 for all web components (WinCC WebNavigator and Information Server).

Executive Summary

Corporate IT cybersecurity audits regularly flag industrial automation systems running older operating systems (Windows XP, Windows Server 2003, Windows 7, Windows Server 2008 R2) for possessing active SSL 2.0 and SSL 3.0 protocol bindings. Automation engineers managing PCS 7 V7.x and V8.x plants frequently worry that disabling these legacy protocols will disrupt critical DCS operations, break PLC communications, or halt WinCC client-server synchronization. This guide references official Siemens Industrial Security guidelines to clarify which communication channels depend on secure sockets, confirms that core DCS communications do not utilize SSL, and outlines the step-by-step registry procedure to disable SSL safely.

Architecture and Fundamental Mechanics

The communication architecture of SIMATIC PCS 7 divides plant data into proprietary control protocols and standard web protocols:
1. Core Process Control Protocols (No SSL/TLS Dependency):
- Plant Bus (AS-OS Communication): Utilizes S7 Communication (RFC 1006 / ISO-on-TCP or ISO Transport over Layer 2 MAC addresses). S7 protocol operates independently of Windows SCHANNEL or SSL/TLS.
- Terminal Bus (OS Server - OS Client): Utilizes Microsoft RPC, Named Pipes, WinCC internal sockets, and Microsoft SQL Server database channels. In PCS 7 V7/V8, these do not rely on SSL 2.0/3.0.
2. Components Utilizing Windows SCHANNEL / SSL:
- Only web-enabled optional packages—specifically WinCC WebNavigator, WinCC DataMonitor, and SIMATIC Information Server—utilize Microsoft IIS and Windows SCHANNEL.
- Legacy SSL 2.0 and SSL 3.0 contain known cryptographic vulnerabilities (e.g., CBC padding oracle attacks like POODLE, CVE-2014-3566).
- Modern Siemens recommendations mandate disabling SSL 2.0 and SSL 3.0 while enabling TLS 1.2 across all PCS 7 PC stations.

Step-by-Step Implementation Procedure

Audit Active SSL/TLS Protocols in Windows Registry:
a. On the PCS 7 Engineering Station or OS Server, open regedit.exe as Administrator.
b. Navigate to the following registry path:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols
c. Inspect the subkeys for SSL 2.0 and SSL 3.0.
Disable SSL 2.0 in Windows SCHANNEL:
a. Under Protocols, create key SSL 2.0 if it does not exist.
b. Under SSL 2.0, create subkeys Client and Server.
c. Inside both Client and Server keys, create a DWORD (32-bit) Value named Enabled and set its value to 0.
d. Create another DWORD (32-bit) Value named DisabledByDefault and set its value to 1.
Disable SSL 3.0 in Windows SCHANNEL:
a. Under Protocols, create key SSL 3.0 if it does not exist.
b. Under SSL 3.0, create subkeys Client and Server.
c. Inside both Client and Server keys, create a DWORD (32-bit) Value named Enabled and set its value to 0.
d. Create another DWORD (32-bit) Value named DisabledByDefault and set its value to 1.
Enable TLS 1.2 (for Systems Supporting Modern Ciphers):
a. Under Protocols, create key TLS 1.2.
b. Under TLS 1.2, create subkeys Client and Server.
c. Inside both keys, create DWORD Value Enabled set to 1, and DisabledByDefault set to 0.
Adjust Internet Options and Restart Station:
a. Open Windows Internet Options via Control Panel.
b. Navigate to the Advanced tab and scroll to 'Security'.
c. Uncheck Use SSL 2.0 and uncheck Use SSL 3.0.
d. Check Use TLS 1.2.
e. Click 'Apply' and restart the computer during an authorized maintenance window.

Verification

Following station reboot, verify that all SIMATIC Manager, CFC, and WinCC Runtime operations start normally.
Confirm that OS clients connect to OS servers and process values update dynamically.
Execute an internal security port scan (e.g., using Nessus or Nmap with --script ssl-enum-ciphers): confirm that ports 443 (HTTPS) and 80 report SSL 2.0 and SSL 3.0 disabled.

Limitations and Operational Precautions

On very old operating systems (Windows XP / Server 2003 in PCS 7 V6.x/V7.0), TLS 1.2 is not natively supported by the OS. In such legacy installations, ensure WebNavigator utilizes isolated, private physical subnets.

Engineer FAQ

Does disabling SSL 2.0 and SSL 3.0 break PCS 7 AS-to-OS communication?

No. AS-to-OS communication uses S7 Communication over ISO/TCP, which does not utilize SSL or Windows SCHANNEL.

Why should SSL 2.0 and 3.0 be disabled in automation systems?

Both protocols suffer from severe cryptographic flaws (such as the POODLE vulnerability) that allow unauthorized decryption of sensitive data.

What PCS 7 components actually use SSL/TLS?

Web-based options such as WinCC WebNavigator, WinCC DataMonitor, and SIMATIC Information Server running over IIS.

Does disabling SSL affect WinCC client-server redundancy?

No. Redundant OS server synchronization uses dedicated TCP/UDP sockets and Microsoft SQL replication, not SSL.

What registry hive controls SSL/TLS protocols in Windows?

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols.

Technical References

Related Tags

Cybersecurity
SSL 3.0
TLS 1.2
SCHANNEL
Industrial Security
PCS 7 V7.0

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Disabling Vulnerable SSL 2.0 and SSL 3.0 Protocols in PCS 7 Environments