Apache Tomcat is a servlet container for the Java Servlet and JavaServer Pages technologies. It was found that, in certain circumstances, it was possible for a malicious web application to replace the XML parsers used by Apache Tomcat to process XSLTs for the default servlet, JSP documents, tag library descriptors , and tag plug-in configuration files. The injected XML parser could then bypass the limits imposed on XML external entities and/or gain access to the XML files processed for other web applications deployed on the same Apache Tomcat instance. All Tomcat users are advised to upgrade to these updated packages, which contain a backported patch to correct this issue. Tomcat must be restarted for this update to take effect.