![]() Mod_evasive Fork of mod_evasive for Apache 2.4. Original module by Deep Logic, Inc WHAT IS MOD_EVASIVE? Mod_evasive is an evasive maneuvers module for Apache to provide evasive action in the event of an HTTP DoS or DDoS attack or brute force attack. Sep 16, 2007 apache 2.2 - mod_evasive. Discussion in 'EasyApache' started by katmai, Sep 14, 2007. Detection is performed by creating an internal dynamic hash table of IP Addresses and URIs, and denying any single IP address from any of the following: • Requesting the same page more than a few times per second • Making more than 50 concurrent requests on the same child per second • Making any requests while temporarily blacklisted (on a blocking list) This method has worked well in both single-server script attacks as well as distributed attacks, but just like other evasive tools, is only as useful to the point of bandwidth and processor consumption (e.g. Nonton saint seiya omega sub indo full episode. The amount of bandwidth and processor required to receive/process/respond to invalid requests), which is why it's a good idea to integrate this with your firewalls and routers. This module instantiates for each listener individually, and therefore has a built-in cleanup mechanism and scaling capabilities. Because of this, legitimate requests are rarely ever compromised, only legitimate attacks. Even a user repeatedly clicking on 'reload' should not be affected unless they do it maliciously. Three different module sources have been provided: Apache v1.3 API: mod_evasive.c Apache v2.0 API: mod_evasive20.c Apache v2.4 API: mod_evasive24.c NSAPI (iPlanet): mod_evasiveNSAPI.c * NOTE: mod_evasiveNSAPI is a port submitted by Reine Persson and is not officially supported as part of the mod_evasive project. HOW IT WORKS A web hit request comes in. The following steps take place: • The IP address of the requestor is looked up on the temporary blacklist • The IP address of the requestor and the URI are both hashed into a 'key'. A lookup is performed in the listener's internal hash table to determine if the same host has requested this page more than once within the past 1 second. • The IP address of the requestor is hashed into a 'key'. A lookup is performed in the listerner's internal hash table to determine if the same host has requested more than 50 objects within the past second (from the same child). If any of the above are true, a 403 response is sent. This conserves bandwidth and system resources in the event of a DoS attack. Additionally, a system command and/or an email notification can also be triggered to block all the originating addresses of a DDoS attack. Once a single 403 incident occurs, mod_evasive now blocks the entire IP address for a period of 10 seconds (configurable). If the host requests a page within this period, it is forced to wait even longer. Since this is triggered from requesting the same URL multiple times per second, this again does not affect legitimate users. The blacklist can/should be configured to talk to your network's firewalls and/or routers to push the attack out to the front lines, but this is not required. Mod_evasive also performs syslog reporting using daemon.alert. Messages will look like this: Aug 6 17:41:49 elijah mod_evasive[23184]: [ID 801097 daemon.alert] Blacklisting address x.x.x.x: possible attack. WHAT IS THIS TOOL USEFUL FOR? This tool is excellent at fending off request-based DoS attacks or scripted attacks, and brute force attacks. When integrated with firewalls or IP filters, mod_evasive can stand up to even large attacks. Its features will prevent you from wasting bandwidth or having a few thousand CGI scripts running as a result of an attack. ![]() If you do not have an infrastructure capable of fending off any other types of DoS attacks, chances are this tool will only help you to the point of your total bandwidth or server capacity for sending 403's. Without a solid infrastructure and address filtering tool in place, a heavy distributed DoS will most likely still take you offline.
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