Hey there! That's a fantastic question that really gets to the heart of what keeps industrial cybersecurity professionals awake. From what I've seen in the field, here are the most common vulnerabilities in supposedly 'secure' PLC-to-cloud pipelines:

1. **Plaintext communication** - Many systems still transmit PLC data in plaintext, especially with legacy protocols like MODBUS. Anyone on the network can read your industrial secrets!

2. **No authentication** - Any device that can access the network can send valid-looking commands to your PLCs. Imagine someone sending 'emergency shutdown' commands from anywhere!

3. **Third-party backdoors** - Vendor support connections often bypass all your security controls. These 'maintenance ports' are prime targets for attackers.

4. **Outdated firmware** - Many industrial devices run on firmware that hasn't been updated in years, with known vulnerabilities just waiting to be exploited.

5. **Poor event logging** - OT devices often have minimal logging capabilities, so security incidents go completely unnoticed until it's too late.

6. **Physical access vulnerabilities** - Anyone with physical access to programming ports can bypass all your network security. Factory floors aren't always as secure as they should be.

The scary part? Many of these vulnerabilities exist in systems that were sold as 'secure solutions.' It's like having a fancy lock on your front door but leaving the back window wide open! What specific industry are you working in? I might have more targeted insights for your particular use case.