Multiple-Session DoS Attack
Table of Contents
Multiple-Session DoS Attack
Configure
DoS Protection Against Flooding of New Sessions by configuring
a DoS Protection policy rule, which determines the criteria that,
when matched by incoming packets, trigger the Protect action.
The DoS Protection profile counts each new connection toward the
Alarm Rate, Activate Rate, and Max Rate thresholds. When the incoming
new connections per second exceed the Activate Rate, the firewall
takes the action specified in the DoS Protection profile.
The following figure and table describe how the Security policy
rules, DoS Protection policy rules and profile work together in
an example.
Sequence
of Events as Firewall Quarantines an IP Address | |
|---|---|
| In this example, an attacker launches a
DoS attack at a rate of 10,000 new connections per second to UDP
port 53. The attacker also sends 10 new connections per second to
HTTP port 80. |
| The new connections match criteria in the
DoS Protection policy rule, such as a source zone or interface,
source IP address, destination zone or interface, destination IP
address, or a service, among other settings. In this example, the
policy rule specifies UDP. The DoS Protection policy rule
also specifies the Protect action and Classified,
two settings that dynamically put the DoS Protection profile settings
into effect. The DoS Protection profile specifies that a Max Rate
of 3000 packets per second is allowed. When incoming packets match
the DoS Protection policy rule, new connections per second are counted toward
the Alert, Activate,
and Max Rate thresholds. You
can also use a Security policy rule to block all traffic from the
source IP address if you deem that address to be malicious all the
time. |
| The 10,000 new connections per second exceed
the Max Rate threshold. When all of the following
occur:
the firewall puts the offending source
IP address on the block list. |
| An IP address on the block list is in quarantine,
meaning all traffic from that IP address is blocked. The firewall
blocks the offending source IP address before additional attack
packets reach the Security policy. |
The following figure describes in more detail what happens after
an IP address that matches the DoS Protection policy rule is put
on the block list. It also describes the Block Duration timer.
Every one second, the firewall allows the IP address to come
off the block list so that the firewall can test the traffic patterns
and determine if the attack is ongoing. The firewall takes the following
action:
- During this one-second test period, the firewall allows packets that don’t match the DoS Protection policy criteria (HTTP traffic in this example) through the DoS Protection policy rules to the Security policy for validation. Very few packets, if any, have time to get through because the first attack packet that the firewall receives after the IP address is let off the block list will match the DoS Protection policy criteria, quickly causing the IP address to be placed back on the block list for another second. The firewall repeats this test each second until the attack stops.
- The firewall blocks all attack traffic from going past the DoS Protection policy rules (the address remains on the block list) until the Block Duration expires.
The 1-second checks illustrated in the preceding figure
occur on firewall models that have multiple dataplane CPUs and a hardware
network processor. All single dataplane systems or systems without
a hardware network processor perform this mitigation in software and
use a 5-second interval.
When the attack stops, the firewall does not put the IP address
back on the block list. The firewall allows non-attack traffic to
proceed through the DoS Protection policy rules to the Security
policy rules for evaluation. You must configure a Security policy
rule to allow or deny traffic because without one, an implicit Deny
rule denies all traffic.
The block list is based on a source zone and source address combination.
This behavior allows duplicate IP addresses to exist as long as they
are in different zones belonging to separate virtual routers.
The Block Duration setting in a DoS Protection profile specifies
how long the firewall blocks the [offending] packets that match
a DoS Protection policy rule. The attack traffic remains blocked
until the Block Duration expires, after which the attack traffic
must again exceed the Max Rate threshold to be blocked again.
If the attacker uses multiple sessions or bots that initiate
multiple attack sessions, the sessions count toward the thresholds in
the DoS Protection profile without a Security policy deny or drop
rule in place. Hence, a single-session attack requires a Security
policy deny or drop rule in order for each packet to count toward
the thresholds; a multiple-session attack does not.
Therefore, the DoS protection against flooding of new sessions
allows the firewall to efficiently defend against a source IP address
while attack traffic is ongoing and to permit non-attack traffic
to pass as soon as the attack stops. Putting the offending IP address
on the block list allows the DoS protection functionality to take
advantage of the block list, which is designed to quarantine all
activity from that source IP address, such as packets with a different
application. Quarantining the IP address from all activity protects
against a modern attacker who attempts a rotating application attack,
in which the attacker simply changes applications to start a new
attack or uses a combination of different attacks in a hybrid DoS
attack. You can monitor blocked IP addresses to
view the block list, remove entries from it, and get additional
information about an IP address on the block list.
Beginning with PAN-OS 7.0.2, it is a change in behavior
that the firewall places the attacking source IP address on the
block list. When the attack stops, non-attack traffic is allowed
to proceed to Security policy enforcement. The attack traffic that
matched the DoS Protection profile and DoS Protection policy rules
remains blocked until the Block Duration expires.