1 Background
Traditional network border defense strategies have focused on a) keeping
intruders out of a network b) protecting internal devices from compromise.
Historically, sites have implemented their security strategy from the border
inward rather than from the endpoint outward.
895,871,345 records have been breached as of 2/21/2016 according to
www.privacyrights.org. Data from this
and similar sites suggests the traditional border network defense model has failed
as a data protection strategy.
Border firewalls are not effective "
protection" devices. They are,
however, excellent "
detection" devices. Why? Firewalls always have to
let data pass through them. Wireless networks negate the effectiveness of a
"border" firewall
by forcing
the network border to be at the endpoint. Whitelisting outbound traffic is a
challenge because most sites are now hosted by companies like Akemai which host
thousands of sites. However, firewalls log packet traffic and this information
is valuable in network forensics.
Continuous monitoring (CM) is an effective strategy to detect and interrupt
data exfiltration.
Seth Misenar and Eric
Conrad [1] list 4 points that show why Continuous Monitoring (CM) is a better
strategy for detecting, preventing and/or interrupting data exfiltration. The 4
points are:
1.
Highly portable devices don’t benefit from the
traditional border network defense model.
2.
Client-side exploitation significantly decreases the
effectiveness of traditional network defense architectures.
3.
Lateral movement inside your network after a compromise
increases the likelihood of endpoint exploitation.
4.
Endpoints must be able to defend themselves and aid in
detection.
Monitoring outbound traffic allows a site to use CM techniques to determine
if a data breach has happened. Unauthorized data transfers are rarely detected
by traditional IDS, IPS or firewalls because intellectual property isn’t just
the standard social security, credit card, driver license, bank/debit account
numbers.
Intellectual property is harder
to classify because the “sensitive” data elements are not the traditional items
that DLP solutions can find. Netflow monitoring techniques can be used to
detect anomalous traffic patterns.
2 Hacker
Attack Strategy
When hackers attack a site, they have 3 primary goals:
- ·
Compromise the endpoint and search for data that
can be stolen.
- ·
Maintain control of the endpoint so it can be
used to attack internal and external systems.
- ·
Be able to destroy the system to eliminate
evidence of a compromise if discovered.
Hackers have adapted to inbound blocks by tricking internal users into
initiating an outbound connection to the malware site. For example, the infostealer
malware class searches the target system for sensitive data such as SSN, CCN,
bank or debit account information, builds a list of files containing these
data, phones “home” to let the hacker know it has data ready for exfiltration.
A compromised machine has to communicate back to the hacker when an attack
is successful. If defenders interrupt the communications/control channel
established, a data exfiltration is prevented or interrupted. This also
prevents the hackers from issuing a “self destruct” command to cover their
tracks.
3 Continuous
Monitoring Defense
Prevention eventually fails but detection and containment are forever. CM
assumes the attackers are inside your network and provides the data to find
them. The defenders' best chance for containing the attack lies in interrupting
hacker goal #2. Here’s how CM can help determine if a data breach of
personally identifiable information (PII) has occurred.
1. The general security strategy should be "protect (encrypt) sensitive
data regardless of location." Protecting devices is obviously
important, however, if the sensitive data is protected then the probability of
a data breach is reduced.
2. Monitoring outbound traffic can detect anomalous outbound transmissions. If
a system is compromised, we ask if there was any sensitive data on the
device.
a. No. Use logs (syslog, eventlog, net flow,
sensor, firewall, IDS, DLP) to isolate the compromised host and if any external
communication has happened. Reinstall/reimage compromised host. Go to step 1.
b. Yes. Run PII search tools like IdentityFinder,
Find_SSN to find out how many records were potentially exposed. If the data
files were encrypted, the chances of a data breach are minimal, go to step 2a.
If PII was in the clear, determine how many unique records were in the file. Go
to step 3.
3. Determine if sensitive data file(s) were exfiltrated from the net. Use
network forensics to determine:
a) when was the earliest communication between
the attacker and the compromised endpoint. This helps us define the window of
exposure.
b) if other internal hosts were accessed from
this compromised host. This helps us define the extent of the attack.
c) the probability of sensitive data breach
occurring by examining netflow data to and from the compromised host.
Historical network data is used to answer the above questions. That data
comes from various sensors each fulfilling a role in CM. The biggest advantage
defenders have is the ability to monitor their network traffic. A system whose
logs have been wiped can still be monitored by examining network traffic.
4 A
Continuous Monitoring Example
How do we detect a suspicious exfiltration? First, you have to establish a
“traffic” baseline to see what is considered “normal” traffic.
Baselining provides you with the answer to
“where do my organization’s packets go? For example, the chart shown in Figure
1 shows the countries that send and receive packets from a network in a month.
The blue bar shows packets that enter the network from a country and the red bar
shows packets that leave the network for a particular country.
Once you profile the inbound/outbound
traffic, you can do a detailed analysis of the traffic.
Packet traffic within the United States is shown at the bottom of the
figure. A possible explanation is the majority of this traffic goes to external
search engines. For example, a search engine query for “Randy Marchany” sends a
relatively short packet stream to a search engine. The results of the search
are usually much greater in size than the original query. Obviously, not all
traffic is web based but having this data allows you to do a detailed analysis
of your network traffic.
Figure 1. Inbound/outbound network traffic by
country
Figure 2 shows a different pattern. It shows a traffic pattern of a large
amount of data packets leaving the network for China, Great Britain and Brazil.
This pattern doesn’t confirm an exfiltration is happening but we certainly have
reason to investigate this traffic further. The analysis confirmed an
exfiltration was happening. The incident response team was able to take steps
to contain and interrupt the data transfer.
Figure 2. Inbound/outbound traffic by country with
anomaly
5 Summary
The traditional network border defense strategy has failed to prevent data
breaches. It's time to change our defensive posture from inbound-centric to
outbound-centric. Continuous Monitoring allows us to determine if a data
exfiltration has happened. CM and network forensics are the difference between
a small, internal breach and a major disaster.
Some good reference books on this topic are "Extrusion Detection:
Security Monitoring for Internal Intrusions" by Richard Bejtlich,
"Network Forensics" by Sherri Davidoff and Jonathan Ham,
"Applied Network Security Monitoring" by Chris Sanders and Jason
Smith.