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Filename : REQUEST-912-DOS-PROTECTION.conf
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# ------------------------------------------------------------------------
# OWASP ModSecurity Core Rule Set ver.3.0.2
# Copyright (c) 2006-2016 Trustwave and contributors. All rights reserved.
#
# The OWASP ModSecurity Core Rule Set is distributed under
# Apache Software License (ASL) version 2
# Please see the enclosed LICENSE file for full details.
# ------------------------------------------------------------------------

#
# Anti-Automation rules to detect Denial of Service attacks.
#
# Description of mechanics:
# When a request hits a non-static resource (TX:STATIC_EXTENSIONS), then a counter for the IP
# address is being raised (IP:DOS_COUNTER). If the counter (IP:DOS_COUNTER) hits a limit
# (TX:DOS_COUNTER_THRESHOLD), then a burst is identified (IP:DOS_BURST_COUNTER) and the
# counter (IP:DOS_COUNTER) is reset. The burst counter expires within a timeout period
# (TX:DOS_BURST_TIME_SLICE).
# If the burst counter (IP:DOS_BURST_COUNTER) is greater equal 2, then the blocking flag
# is being set (IP:DOS_BLOCK). The blocking flag (IP:DOS_BLOCK) expires within a timeout
# period (TX:DOS_BLOCK_TIMEOUT). All this counting happens in phase 5.
# There is a stricter sibling to this rule (912170) in paranoia level 2, where the
# burst counter check (IP:DOS_BURST_COUNTER) hits at greater equal 1.
#
# The blocking is done in phase 1: When the blocking flag is encountered (IP:DOS_BLOCK),
# then the request is dropped without sending a response. If this happens, then a
# counter is # raised (IP:DOS_BLOCK_COUNTER).
# When an IP address is blocked for the first time, then the blocking is reported in a
# message and a flag (IP:DOS_BLOCK_FLAG) is set. This flag expires in 60 seconds.
# When an IP address is blocked and the flag (IP:DOS_BLOCK_FLAG) is set, then the
# blocking is not being reported (to prevent a flood of alerts). When the flag
# (IP:DOS_BLOCK_FLAG) has expired and a new request is being blocked, then the
# counter (IP:DOS_BLOCK_COUNTER) is being reset to 0 and the block is being treated
# as the first block (-> alert).
# In order to be able to display the counter (IP:DOS_BLOCK_COUNTER) and resetting
# it at the same time, we copy the counter (IP:DOS_BLOCK_COUNTER) into a different
# variable (TX:DOS_BLOCK_COUNTER), which is then displayed in turn.
#
# Variables:
# IP:DOS_BLOCK              Flag if an IP address should be blocked
# IP:DOS_BLOCK_COUNTER      Counter of blocked requests
# IP:DOS_BLOCK_FLAG         Flag keeping track of alert. Flag expires after 60 seconds.
# IP:DOS_BURST_COUNTER      Burst counter
# IP:DOS_COUNTER            Request counter (static resources are ignored)
# TX:DOS_BLOCK_COUNTER      Copy of IP:DOS_BLOCK_COUNTER (needed for display reasons)
# TX:DOS_BLOCK_TIMEOUT      Period in seconds a blocked IP will be blocked
# TX:DOS_COUNTER_THRESHOLD  Limit of requests, where a burst is identified
# TX:DOS_BURST_TIME_SLICE   Period in seconds when we will forget a burst
# TX:STATIC_EXTENSIONS      Paths which can be ignored with regards to DoS
#
# As a precondition for these rules, please set the following three variables:
#  - TX:DOS_BLOCK_TIMEOUT
#  - TX:DOS_COUNTER_THRESHOLD
#  - TX:DOS_BURST_TIME_SLICE
#
# And make sure that TX:STATIC_EXTENSIONS is also set.
#

#
# -= Paranoia Level 0 (empty) =- (apply unconditionally)
#

#
# Skip if variables defining DoS protection are not set
#
SecRule &TX:dos_burst_time_slice "@eq 0" \
	"id:912100,\
	phase:1,\
	t:none,\
	nolog,\
	pass,\
	chain,\
	skipAfter:END_DOS_PROTECTION_CHECKS"
	SecRule &TX:dos_counter_threshold "@eq 0" "chain"
	SecRule &TX:dos_block_timeout "@eq 0"

SecRule &TX:dos_burst_time_slice "@eq 0" \
	"id:912110,\
	phase:5,\
	t:none,\
	nolog,\
	pass,\
	chain,\
	skipAfter:END_DOS_PROTECTION_CHECKS"
	SecRule &TX:dos_counter_threshold "@eq 0" "chain"
	SecRule &TX:dos_block_timeout "@eq 0"


SecRule TX:PARANOIA_LEVEL "@lt 1" "phase:1,id:912011,nolog,pass,skipAfter:END-REQUEST-912-DOS-PROTECTION"
SecRule TX:PARANOIA_LEVEL "@lt 1" "phase:2,id:912012,nolog,pass,skipAfter:END-REQUEST-912-DOS-PROTECTION"
#
# -= Paranoia Level 1 (default) =- (apply only when tx.paranoia_level is sufficiently high: 1 or higher)
#

#
# -=[ Anti-Automation / DoS Protection : Block ]=-
#

#
# Block and track # of requests and log
#
SecRule IP:DOS_BLOCK "@eq 1" \
	"chain,\
	phase:1,\
	id:912120,\
	drop,\
	tag:'application-multi',\
	tag:'language-multi',\
	tag:'platform-multi',\
	tag:'attack-dos',\
	msg:'Denial of Service (DoS) attack identified from %{tx.real_ip} (%{tx.dos_block_counter} hits since last alert)'"
	SecRule &IP:DOS_BLOCK_FLAG "@eq 0" \
		"setvar:ip.dos_block_counter=+1,\
		setvar:ip.dos_block_flag=1,\
		expirevar:ip.dos_block_flag=60,\
		setvar:tx.dos_block_counter=%{ip.dos_block_counter},\
		setvar:ip.dos_block_counter=0"


#
# Block and track # of requests but don't log
#
SecRule IP:DOS_BLOCK "@eq 1" \
	"phase:1,\
	id:912130,\
	t:none,\
	drop,\
	nolog,\
	tag:'application-multi',\
	tag:'language-multi',\
	tag:'platform-multi',\
	tag:'attack-dos',\
	setvar:ip.dos_block_counter=+1"


#
# -=[ Anti-Automation / DoS Protection: Count requests ]=-
#

#
# Skip if we have blocked the request
#
SecRule IP:DOS_BLOCK "@eq 1" \
	"phase:5,\
	id:912140,\
	t:none,\
	nolog,\
	tag:'application-multi',\
	tag:'language-multi',\
	tag:'platform-multi',\
	tag:'attack-dos',\
	pass,\
	skipAfter:END_DOS_PROTECTION_CHECKS"


#
# DOS Counter: Count the number of requests to non-static resources
#
SecRule REQUEST_BASENAME ".*?(\.[a-z0-9]{1,10})?$" \
	"phase:5,\
	id:912150,\
	t:none,\
	t:lowercase,\
	nolog,\
	pass,\
	tag:'application-multi',\
	tag:'language-multi',\
	tag:'platform-multi',\
	tag:'attack-dos',\
	capture,\
   	setvar:tx.extension=/%{TX.1}/,\
	chain"
	SecRule TX:EXTENSION "!@within %{tx.static_extensions}" \
		"setvar:ip.dos_counter=+1"


#
# Check DOS Counter
# If the request count is greater than or equal to user settings,
# we raise the burst counter. This happens via two separate rules:
# - 912160: raise from 0 to 1
# - 912161: raise from 1 to 2
#
# This approach with two rules avoids raising the burst counter
# from 0 to 2 via two concurrent requests. We do not raise the
# burst counter beyond 2.
#
#
SecRule IP:DOS_COUNTER "@ge %{tx.dos_counter_threshold}" \
	"phase:5,\
	id:912160,\
	t:none,\
	nolog,\
	pass,\
	tag:'application-multi',\
	tag:'language-multi',\
	tag:'platform-multi',\
	tag:'attack-dos',\
	chain"
	SecRule &IP:DOS_BURST_COUNTER "@eq 0" \
		"setvar:ip.dos_burst_counter=1,\
		expirevar:ip.dos_burst_counter=%{tx.dos_burst_time_slice},\
		setvar:!ip.dos_counter"


SecRule IP:DOS_COUNTER "@ge %{tx.dos_counter_threshold}" \
	"phase:5,\
	id:912161,\
	t:none,\
	nolog,\
	pass,\
	tag:'application-multi',\
	tag:'language-multi',\
	tag:'platform-multi',\
	tag:'attack-dos',\
	chain"
	SecRule &IP:DOS_BURST_COUNTER "@ge 1" \
		"setvar:ip.dos_burst_counter=2,\
		expirevar:ip.dos_burst_counter=%{tx.dos_burst_time_slice},\
		setvar:!ip.dos_counter"


#
# Check DOS Burst Counter and set Block
# Check the burst counter - if greater than or equal to 2, then we set the IP
# block variable for a given expiry and issue an alert.
#
SecRule IP:DOS_BURST_COUNTER "@ge 2" \
	"phase:5,\
	id:912170,\
	t:none,\
	log,\
	pass,\
	tag:'application-multi',\
	tag:'language-multi',\
	tag:'platform-multi',\
	tag:'attack-dos',\
	msg:'Potential Denial of Service (DoS) Attack from %{tx.real_ip} - # of Request Bursts: %{ip.dos_burst_counter}',\
	setvar:ip.dos_block=1,\
	expirevar:ip.dos_block=%{tx.dos_block_timeout}"



SecRule TX:PARANOIA_LEVEL "@lt 2" "phase:1,id:912013,nolog,pass,skipAfter:END-REQUEST-912-DOS-PROTECTION"
SecRule TX:PARANOIA_LEVEL "@lt 2" "phase:2,id:912014,nolog,pass,skipAfter:END-REQUEST-912-DOS-PROTECTION"
SecRule TX:PARANOIA_LEVEL "@lt 2" "phase:5,id:912019,nolog,pass,skipAfter:END-REQUEST-912-DOS-PROTECTION"
#
# -= Paranoia Level 2 =- (apply only when tx.paranoia_level is sufficiently high: 2 or higher)
#

#
# Check DOS Burst Counter and set Block
# Check the burst counter - if greater than or equal to 1, then we set the IP
# block variable for a given expiry and issue an alert.
#
# This is a stricter sibling of rule 912170.
#
SecRule IP:DOS_BURST_COUNTER "@ge 1" \
	"phase:5,\
	id:912171,\
	t:none,\
	log,\
	pass,\
	tag:'application-multi',\
	tag:'language-multi',\
	tag:'platform-multi',\
	tag:'attack-dos',\
	tag:'paranoia-level/2',\
	msg:'Potential Denial of Service (DoS) Attack from %{tx.real_ip} - # of Request Bursts: %{ip.dos_burst_counter}',\
	setvar:ip.dos_block=1,\
	expirevar:ip.dos_block=%{tx.dos_block_timeout}"



SecRule TX:PARANOIA_LEVEL "@lt 3" "phase:1,id:912015,nolog,pass,skipAfter:END-REQUEST-912-DOS-PROTECTION"
SecRule TX:PARANOIA_LEVEL "@lt 3" "phase:2,id:912016,nolog,pass,skipAfter:END-REQUEST-912-DOS-PROTECTION"
#
# -= Paranoia Level 3 =- (apply only when tx.paranoia_level is sufficiently high: 3 or higher)
#



SecRule TX:PARANOIA_LEVEL "@lt 4" "phase:1,id:912017,nolog,pass,skipAfter:END-REQUEST-912-DOS-PROTECTION"
SecRule TX:PARANOIA_LEVEL "@lt 4" "phase:2,id:912018,nolog,pass,skipAfter:END-REQUEST-912-DOS-PROTECTION"
#
# -= Paranoia Level 4 =- (apply only when tx.paranoia_level is sufficiently high: 4 or higher)
#



#
# -= Paranoia Levels Finished =-
#
SecMarker "END-REQUEST-912-DOS-PROTECTION"

SecMarker END_DOS_PROTECTION_CHECKS