This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; version 2
of the License.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.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 tool, and can be easily configured to talk to ipchains, firewalls, routers, and etcetera.
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:
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. 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.
Five different module sources have been provided:
NOTE: mod_evasiveNSAPI is a port submitted by Reine Persson reiper@rsv.se and is not officially supported as part of the mod_evasive project.
A web hit request comes in. The following steps take place:
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.
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.
dpkg -i libapache2-mod-evasive.debThere is a mod_evasive24win.c that includes all the features from the Linux
version except DOSEmailNotify. It should work fine. Unfortunately I do not have
a Windows development or testing environment. This means I can't test it, and I
don't know how to install it. If you know how to do these things, please let me
know and I'll update the instructions here.
As always, any bugs may also be filed through Github and I'll see what I can do.
mv mod_evasive24.c mod_evasive.c$APACHE_ROOT/bin/apxs -i -a -c mod_evasive.cNote: This version is missing some features.
Without DSO Support:
mv mod_evasive13.c mod_evasive.c./configure --add-module=src/modules/evasive/mod_evasive.cmake && make installWith DSO Support, Ensim, or CPanel:
$APACHE_ROOT/bin/apxs -iac mod_evasive.cSunONE (iPlanet,netscape) Installation
Tested on: iPlanet 4.1sp12 iPlanet 6.0sp5
Edit compile script for your environment and compile mod_evasiveNSAPI.c to a shared library.
mod_evasive has default options configured, but you may also add the following block to your httpd.conf:
<IfModule mod_evasive.c>
DOSEnabled true
DOSHashTableSize 3097
DOSPageCount 2
DOSSiteCount 50
DOSPageInterval 1
DOSSiteInterval 1
DOSBlockingPeriod 10
</IfModule>Optionally you can also add the following directives:
DOSEmailNotify you@yourdomain.com
DOSSystemCommand "su - someuser -c '/sbin/... %s ...'"
DOSLogDir "/var/lock/mod_evasive"
DOSWhitelist 127.0.0.1
DOSWhitelistUri whitelist.*regex
DOSHTTPStatus 429You will also need to add this line if you are building with dynamic support:
AddModule mod_evasive.cLoadModule evasive_module modules/mod_evasive.so(This line is already added to your configuration by apxs)
SunONE (iPlanet,Netscape) Configuration
Edit obj.conf:
Init fn="load-modules" funcs="mod_evasive_init,mod_evasive_check" shlib="/opt/ns-4.1/plugins/lib/mod_evasive.sl"
Init fn="mod_evasive_init" DOSPageCount=2 DOSSiteCount=50 DOSPageInterval=1 DOSSiteInterval=1 DOSBlockingPeriod=10 DOSWhitelist="10.60.0.7,10.65.0.10"In the default object:
PathCheck fn=mod_evasive_checkOr an own object
<Object name="evasive" ppath="/DoSProtectedArea*">
NameTrans fn=mod_evasive_check
</Object>Edit magnus.conf:
Init fn="load-modules" funcs="mod_evasive_init,mod_evasive_check" shlib="/opt/iplanet-6.0/plugins/lib/mod_evasive.sl"
Init fn="mod_evasive_init" DOSWhitelist="10.60.0.7,10.65.0.10"Edit obj.conf: In the default object:
PathCheck fn=mod_evasive_check
```
Or an own object
# Features
## DOSEnabled
Set to `true` to enable mod_evasive. Set globally to enable everywhere, or only
in specific VirtualHosts otherwise.
## DOSHashTableSize
The hash table size defines the number of top-level nodes for each child's
hash table. Increasing this number will provide faster performance by
decreasing the number of iterations required to get to the record, but
consume more memory for table space. You should increase this if you have
a busy web server. The value you specify will automatically be tiered up to
the next prime number in the primes list (see mod_evasive.c for a list
of primes used).
## DOSPageCount
This is the threshhold for the number of requests for the same page (or URI)
per page interval. Once the threshhold for that interval has been exceeded,
the IP address of the client will be added to the blocking list.
## DOSSiteCount
This is the threshhold for the total number of requests for any object by
the same client on the same listener per site interval. Once the threshhold
for that interval has been exceeded, the IP address of the client will be added
to the blocking list.
## DOSPageInterval
The interval for the page count threshhold; defaults to 1 second intervals.
## DOSSiteInterval
The interval for the site count threshhold; defaults to 1 second intervals.
## DOSBlockingPeriod
The blocking period is the amount of time (in seconds) that a client will be
blocked for if they are added to the blocking list. During this time, all
subsequent requests from the client will result in a 403 (Forbidden) and
the timer being reset (e.g. another 10 seconds). Since the timer is reset
for every subsequent request, it is not necessary to have a long blocking
period; in the event of a DoS attack, this timer will keep getting reset.
## DOSEmailNotify
If this value is set, an email will be sent to the address specified
whenever an IP address becomes blacklisted. A locking mechanism using /tmp
prevents continuous emails from being sent.
NOTE: Be sure MAILER is set correctly in mod_evasive.c. The default is
"/bin/mail -t %s" where %s is used to denote the destination email
address set in the configuration. If you are running on linux or some
other operating system with a different type of mailer, you'll need to
change this.
## DOSSystemCommand
If this value is set, the system command specified will be executed
whenever an IP address becomes blacklisted. This is designed to enable
system calls to ip filter or other tools. A locking mechanism using /tmp
prevents continuous system calls. Use %s to denote the IP address of the
blacklisted IP.
## DOSLogDir
Choose an alternative temp directory
By default "/tmp" will be used for locking mechanism, which opens some
security issues if your system is open to shell users.
http://security.lss.hr/index.php?page=details&ID=LSS-2005-01-01
In the event you have nonprivileged shell users, you'll want to create a
directory writable only to the user Apache is running as (usually root),
then set this in your httpd.conf.
## DOSHTTPStatus
Choose an alternative HTTP status code for the reply to blocked clients.
By default mod_evasive returns 403 Forbidden to blocked clients. This
directive allows any other HTTP code known to Apache to be used instead.
## Whitelisting IP Addresses
IP addresses of trusted clients can be whitelisted to insure they are never
denied. The purpose of whitelisting is to protect software, scripts, local
searchbots, or other automated tools from being denied for requesting large
amounts of data from the server. Whitelisting should *not* be used to add
customer lists or anything of the sort, as this will open the server to abuse.
This module is very difficult to trigger without performing some type of
malicious attack, and for that reason it is more appropriate to allow the
module to decide on its own whether or not an individual customer should be
blocked.
To whitelist an address (or range) add an entry to the Apache configuration
in the following fashion:
DOSWhitelist 127.0.0.1
DOSWhitelist 127.0.0.*
Wildcards can be used on up to the last 3 octets if necessary. Multiple
DOSWhitelist commands may be used in the configuration.
You can add several entries.
## Whitelisting URI's
Specific URI's can be whitelisted to insure they are never denied. Some
clients may repeatedly request the same URI (due to bugs, or for other
reasons), and subsequently be blocked from making other (valid) requests. If
you want, you may whitelist these URI's so these clients won't be blocked.
Use with caution.
To whitelist a URI add an entry to the Apache configuration
in the following fashion:
DOSWhitelistUri /path/to/whitelisted/resource
DOSWhitelistUri .*whitelisted.*
`DOSWhitelistUri` supports perl-style regex and matches the whole request URI
(everything between the domain name and the ?) against this regex.
You can add several entries.
> [!CAUTION]
> This is currently UNTESTED on Windows, I'm not sure it will even compile. Let
> me know about any issues, or even if it does work as expected! :pray:
# Tweaking Apache
The keep-alive settings for your children should be reasonable enough to
keep each child up long enough to resist a DOS attack (or at least part of
one). Remember, it is the child processes that maintain their own internal
IP address tables, and so when one exits, so does all of the IP information it
had. For every child that exits, another 5-10 copies of the page may get
through before putting the attacker back into '403 Land'. With this said,
you should have a very high MaxRequestsPerChild, but not unlimited as this
will prevent cleanup.
You'll want to have a MaxRequestsPerChild set to a non-zero value, as
DosEvasive cleans up its internal hashes only on exit. The default
MaxRequestsPerChild is usually 10000. This should suffice in only allowing
a few requests per 10000 per child through in the event of an attack (although
if you use DOSSystemCommand to firewall the IP address, a hole will no
longer be open in between child cycles).
# Testing
Want to make sure it's working? Run test.pl, and view the response codes.
It's best to run it several times on the same machine as the web server until
you get 403 Forbidden messages. Some larger servers with high child counts
may require more of a beating than smaller servers before blacklisting
addresses.
Please don't use this script to DoS others without their permission.
# Known bugs and Issues
- This module appears to conflict with the Microsoft Frontpage Extensions.
Frontpage sucks anyway, so if you're using Frontpage I assume you're asking
for problems, and not really interested in conserving server resources anyway.
- When used together with mod_rewrite, mod_rewrite seems to take priority over
this. This means that Apache will always rewrite the url even during an
attack, and mod_evasive will be ineffective on the original url (but not on
the rewritten url). For example, if you use mod_rewrite to redirect http to
https, the redirect to https will always happen. In this case you should
enable mod_evasive on the https virtualhost only, as it will not have any
effect on the http virtualhost.
- Using mpm_itk instead of the default mpm_event will cause mod_evasive to never
get triggered.
# Feedback
Please use the Github issues feature to tell me about any bugs, missing features, ...