An Information Exposure through Discrepancy vulnerability exists in the embedded web servers in all Modicon M340, Premium, Quantum PLCs and BMXNOR0200 where the web server sends different responses in a way that exposes security-relevant information about the state of the product, such as whether a particular operation was successful or not.
https://www.schneider-electric.com/en/download/document/SEVD-2018-327-01/
https://github.com/SadFud/Exploits/tree/master/Real%20World/SCADA%20-%20IOT%20Systems/CVE-2018-7812