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A denial of service vulnerability has been found in the way the multiple overlapping ranges are handled by the Apache HTTPD server prior to version 2.2.20: http://seclists.org/fulldisclosure/2011/Aug/175 An attack tool is circulating in the wild. Active use of this tool has been observed. The attack can be done remotely and with a modest number of requests can cause very significant memory and CPU usage on the server. The default Apache httpd installations version 2.0 prior to 2.0.65 and version 2.2 prior to 2.2.20 are vulnerable. Apache 2.2.20 does fix this issue; however with a number of side effects (see release notes). Version 2.2.21 corrects a protocol defect in 2.2.20, and also introduces the MaxRanges directive. Version 2.0.65 includes fix for this vulnerability. Apache 1.3 is NOT vulnerable. However as explained in the background section in more detail - this attack does cause a significant and possibly unexpected load. You are advised to review your configuration in that light.
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