Craft CMS 2.6.3000 allows remote attackers to execute arbitrary PHP code by using the "Assets->Upload files" screen and then the "Replace it" option, because this allows a .jpg file to have embedded PHP code, and then be renamed to a .php extension.
Craft CMS before 2.6.2976 allows XSS attacks because an array returned by HttpRequestService::getSegments() and getActionSegments() need not be zero-based. NOTE: this vulnerability exists because of an incomplete fix for CVE-2017-8052.