The integrated web server on Siemens SCALANCE M-800 and S615 modules with firmware before 4.02 does not set the secure flag for the session cookie in an https session, which makes it easier for remote attackers to capture this cookie by intercepting its transmission within an http session.
https://ics-cert.us-cert.gov/advisories/ICSA-16-271-01
http://www.siemens.com/cert/pool/cert/siemens_security_advisory_ssa-342135.pdf