Siemens SIMATIC S7-1500 CPU devices before 1.8.3 allow remote attackers to bypass a replay protection mechanism via packets on TCP port 102.
https://ics-cert.us-cert.gov/advisories/ICSA-16-040-02
https://cert-portal.siemens.com/productcert/pdf/ssa-253230.pdf
http://www.siemens.com/cert/pool/cert/siemens_security_advisory_ssa-253230.pdf