Untrusted search path vulnerability in Siemens SIMATIC STEP7 before 5.5 SP1, as used in SIMATIC PCS7 7.1 SP3 and earlier and other products, allows local users to gain privileges via a Trojan horse DLL in a STEP7 project folder.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2012-2993
http://www.us-cert.gov/control_systems/pdf/ICSA-12-205-02.pdf