The remote web server is vulnerable to a denial of service attack.
Versions of Apache 2.2 earlier than 2.2.21 are potentially affected by a denial of service vulnerability. An error exists in the mod_proxy_ajp module that can allow specially crafted HTTP requests to cause a backend server to temporarily enter an error state. This vulnerability only occurs when mod_proxy_ajp is used along with mod_proxy_balancer.
Upgrade to Apache version 2.2.21 or later.