Red Hat Security Advisory 2012-0077-01 - JBoss Web is a web container based on Apache Tomcat. It provides a single deployment platform for the JavaServer Pages and Java Servlet technologies. A flaw was found in the way JBoss Web handled UTF-8 surrogate pair characters. If JBoss Web was hosting an application with UTF-8 character encoding enabled, or that included user-supplied UTF-8 strings in a response, a remote attacker could use this flaw to cause a denial of service on the JBoss Web server. It was found that the Java hashCode() method implementation was susceptible to predictable hash collisions. A remote attacker could use this flaw to cause JBoss Web to use an excessive amount of CPU time by sending an HTTP request with a large number of parameters whose names map to the same hash value. This update introduces a limit on the number of parameters and headers processed per request to mitigate this issue. The default limit is 512 for parameters and 128 for headers. These defaults can be changed by setting the "-Dorg.apache.tomcat.util.http.Parameters.MAX_COUNT=x" and "-Dorg.apache.tomcat.util.http.MimeHeaders.MAX_COUNT=x" system properties as JAVA_OPTS entries in "jboss-as-web/bin/run.conf".
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