java/org/apache/catalina/servlets/DefaultServlet.java in the default servlet in Apache Tomcat before 6.0.40, 7.x before 7.0.53, and 8.x before 8.0.4 does not properly restrict XSLT stylesheets, which allows remote attackers to bypass security-manager restrictions and read arbitrary files via a crafted web application that provides an XML external entity declaration in conjunction with an entity reference, related to an XML External Entity (XXE) issue.