Apache Tomcat 4.1.0 through 4.1.39 5.5.0 through 5.5.27 and 6.0.0 through 6.0.18 when the Java AJP connector and mod_jk load balancing are used allows remote attackers to cause a denial of service (application outage) via a crafted request with invalid headers related to temporary blocking of connectors that have encountered errors as demonstrated by an error involving a malformed HTTP Host header.