Sharetronix 3.1.1.3, 3.1.1, and earlier allows remote attackers to execute arbitrary PHP code via the (1) activities_text parameter to services/activities/set or (2) comments_text parameter to services/comments/set, which is not properly handled when executing the preg_replace function with the e modifier.
https://exchange.xforce.ibmcloud.com/vulnerabilities/89503
http://www.securityfocus.com/bid/64102
http://secunia.com/secunia_research/2013-8/