Red Hat: RHSA-2012-0475-01 Moderate: Tomcat6 CPU Denial of Service

Apache Tomcat is a servlet container for the Java Servlet and JavaServer Pages (JSP) technologies.
It was found that the Java hashCode() method implementation was susceptible to predictable hash collisions. A remote attacker could use this flaw to cause Tomcat 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 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 org.apache.tomcat.util.http.Parameters.MAX_COUNT and org.apache.tomcat.util.http.MimeHeaders.MAX_COUNT system properties. (CVE-2011-4858)
It was found that Tomcat did not handle large numbers of parameters and large parameter values efficiently. A remote attacker could make Tomcat use an excessive amount of CPU time by sending an HTTP request containing a large number of parameters or large parameter values. This update introduces limits on the number of parameters and headers processed per request to address this issue. Refer to the CVE-2011-4858 description for information about the org.apache.tomcat.util.http.Parameters.MAX_COUNT and org.apache.tomcat.util.http.MimeHeaders.MAX_COUNT system properties. (CVE-2012-0022)
Red Hat would like to thank oCERT for reporting CVE-2011-4858. oCERT acknowledges Julian Wälde and Alexander Klink as the original reporters of CVE-2011-4858.
Users of Tomcat should upgrade to these updated packages, which correct these issues. Tomcat must be restarted for this update to take effect.