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. It is also designed to be a detection and network management tool, and can be easily configured to talk to ipchains, firewalls, routers, and etcetera. mod_evasive presently reports abuses via email and syslog facilities.

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)

Installation

apt-get install libapache2-mod-evasive
mkdir /var/log/apache2/mod_evasive
chown www-data:www-data /var/log/apache2/mod_evasive

Configuration

Create a new file

vi /etc/apache2/conf.d/01_modevasive.conf

with this content

<ifmodule mod_evasive20.c>
 DOSHashTableSize 3097
 DOSPageCount 2
 DOSSiteCount 50
 DOSPageInterval 1
 DOSSiteInterval 1
 DOSBlockingPeriod 10
 DOSLogDir /var/log/apache2/mod_evasive
 DOSEmailNotify root@localhost
 DOSWhitelist 127.0.0.1
</ifmodule>

Restart Apache to activate the new module

/etc/init.d/apache2 restart

Documentation

  • DOSHashTableSize: Size of the hash table used to store the IPs.
  • DOSPageCount: Number of pages allowed per DOSPageInterval.
  • DOSPageInterval: Time in seconds used by DOSPageCount.
  • DOSSiteCount: Number of objects allowed per DOSSiteInterval.
  • DOSSiteInterval: Time in seconds used by DOSSiteCount.
  • DOSBlockingPeriod: Time in seconds that IPs will be banned. If an IP tries to access the server within this period, the count will be restarted.
  • DOSLogDir: Optional. Directory to store the logs. If not specified, /tmp will be used.
  • DOSEmailNotify: Optional. Mail where notifications will be sent.

DOSSystemCommand: is Optional.&160; Command to execute if an IP is blocked. For example using iptables:

DOSSystemCommand "/sbin/iptables -I INPUT -p tcp --dport 80 -s %s -j DROP"