A Security Information Management (SIM) system can contain a tremendous amount of
sensitive information. This is because it receives event logs from security systems
throughout a network. These logs potentially contain information that can be used to target
attacks at sensitive systems. For example, intrusion detection system (IDS) logs can contain
actual packets seen on the network. Some of these packets can be decoded with freely
available packet analyzers to find usernames and passwords that your employees might be
using to access websites, e-mail systems, and network devices.
A Security Information Management (SIM) system can contain a tremendous amount of
sensitive information. This is because it receives event logs from security systems
throughout a network. These logs potentially contain information that can be used to target
attacks at sensitive systems. For example, intrusion detection system (IDS) logs can contain
actual packets seen on the network. Some of these packets can be decoded with freely
available packet analyzers to find usernames and passwords that your employees might be
using to access websites, e-mail systems, and network devices.
Although security people always encourage users to select unique passwords for company
networks, the reality is that many users tend to reuse passwords both for work and home
activities. If an employee has decided to use his work network password as his personal
web-based e-mail password, if an attacker discovers the cleartext authentication for web
e-mail, he has also discovered an account on your network in which to begin nefarious
activities.
As a topology-aware SIM product, the Cisco Security Monitoring, Analysis, and Response
System (CS-MARS) often contains even more sensitive information. The most accurate
method of maintaining the network topology awareness within MARS is by discovering
each network device. This involves configuring access information for MARS to
authenticate to the devices, retrieve interface information, and periodically rediscover it.
From within the user interfaces, both the command-line interface (CLI) and web user
interface, device authentication information is masked to prevent anyone from using the
console to gain unauthorized information. However, if an attacker gains access to the base
operating system, or gains physical access to the appliance, he could use that access to
retrieve all information contained on the hard drives, which could include device
authentication information. He can also use that access to install back doors to allow remote
access at any time.
This chapter describes recommendations for securing MARS appliances, both physically
and electronically. It also provides detailed insight into the TCP and User Datagram
Protocol (UDP) ports that MARS requires for communication with other MARS
appliances, in addition to monitored security, network, and other devices.
PHYSICAL SECURITY
You cannot properly address network security without also addressing physical security.
This is evident with common sense and in the various regulations addressed in Chapter 2,
“Regulatory Challenges in Depth.” All the network security in the world is worthless if
someone with malicious intent can gain physical access to the target.
Make sure that the hosts on your security management network, and MARS specifically,
reside in a protected facility. At the very least, they should be locked in a room that is
inaccessible to the public and staff without a specific business need. Ideally, security
management resides in a datacenter that exercises strong controls. Staff with access rights
to the facility need to have a security badge and need to sign in, either on paper or
electronically, before entering. In Chapter 2, the Payment Card Industry (PCI) data security
standard has good recommendations that datacenters everywhere should attempt to adhere
to, even if your facility is not affected by PCI requirements.
INHERENT SECURITY OF MARS APPLIANCES
Management access to all MARS appliances is through Secure Socket Layer (SSL)–
encrypted web access (HTTPS) and Secure Shell (SSH). These protocols, using TCP/443
and TCP/22, respectively, are inherently secure because they use encryption,
authentication, and authorization. Unencrypted protocols that serve similar functions, such
as HTTP and Telnet, are both disabled on the MARS appliance and cannot be enabled.
MARS appliances are hardened Linux servers that run a variety of services, including
Oracle, Apache HTTP Server, and more. With each software update, the various services
and drivers on MARS are updated with new versions or patches to mitigate against any
newly discovered vulnerabilities. Additionally, unnecessary or unused services are disabled
to prevent them from being potential weaknesses in the security of the appliances.
This hardening of the operating system provides a good starting level of security. However,
it is not enough. You need to take into consideration the sensitivity of the information
contained on the MARS appliances when considering how secure the appliances should be.
You should have a well-defined written plan for preventing MARS from being used as an
attack vector on your network. This includes placing the appliance in a part of your network
that is protected from the rest of the network by a firewall and an IDS.
Without protecting MARS with a firewall and IDS or intrusion prevention system (IPS), a
hacker can try to find vulnerabilities, either in the management protocols or in other
protocols that are used to monitor security or network devices. The additional protections
provided by the firewall or IDS/IPS allow you to limit the exposure to attacks while also
creating an audit trail of attempted attacks.
As an example, consider SSH, the command-line method of administering MARS
remotely. In the past, a number of vulnerabilities have appeared in the OpenSSH
application, which provides this service for MARS. No known vulnerabilities exist in the
SSH service that MARS uses at this time. However, at some time in the future, a new
vulnerability might be found. For this reason, it makes sense to restrict the capability of
computers to establish an SSH connection to MARS unless they are connected to a specific
network or set of networks at your location. A stateful inspection firewall is the ideal device
for providing these limits. A network IDS or IPS that is regularly updated with new
signatures can detect when someone is attempting to use a known vulnerability to
compromise the MARS appliance.
Another example, also using SSH, involves a brute-force password attack against the
MARS appliance. In this attack, an attacker repeatedly uses a dictionary of passwords,
using a script, to attempt to crack the password that administers the MARS appliance.
MARS is especially vulnerable to this type of attack because the administrator’s username
is a well-known value—pnadmin—and this is the only username that can use SSH. This
example is mitigated using the same methods as the first example. First, placing MARS on
a protected network, with a stateful inspection firewall separating it from the rest of your
network, allows you to limit connection attempts to a limited number of devices or
networks on your company’s network. Additionally, a network IDS or IPS can detect
multiple login attempts, whether by SSH or web-based. The detection by an IDS can notify
the appropriate personnel, or an IPS can prevent further attempts.
SECURITY MANAGEMENT NETWORK
As a best practice, you should create a network as a security management network if you
don’t already have one. This network should contain various servers used for administering
and monitoring the security of your network. The entire network should be protected by a
firewall and IDS/IPS. Access to it should be tightly restricted, and any remote access to it
should be through a Virtual Private Network (VPN).
Examples of hosts that should reside on this network include the following:
- MARS global controller (GC)
- MARS local controller (LC), if practical
- MARS archive server
- Firewall management consoles, such as Cisco Security Manager or Check Point
SmartCenter
- IDS/IPS/HIPS management consoles
- Any existing syslog servers
- Vulnerability scanning hosts
The systems that reside on your management networks are some of the most sensitive in
your organization. They often contain the keys to the kingdom, and for this reason, the
management networks are targets of attackers. After an attacker has compromised a host on
a management network, an open freeway often exists to other systems because of the trust
assigned to hosts on the management network.
Don’t cut corners on network hardware that you use on your security management network.
Install switches that support security features. You might want to consider configuring
features such as private VLANs, which provide isolation between hosts on the same
network. Other switch security features, such as the capability to prevent VLAN hopping,
should also be considered.
MARS COMMUNICATIONS REQUIREMENTS
Before you can protect MARS with a firewall, you first need to understand which TCP and
UDP ports MARS requires to operate properly, and which of these carry outbound or
inbound traffic. Table 4-1 provides a summary of all communications when MARS and the
various monitored devices are all configured with default ports. Many or all of these can be
changed, and you might need to modify this table for your installation.
NETWORK SECURITY RECOMENDATIONS
As you can see, depending on your environment and the location of hosts, a complex set of
rules can be required on your firewall. Don’t let the complexity prevent you from properly
configuring the firewall, however. A little work initially can mean a better, more secure
monitoring solution.
The following sections discuss issues regarding firewall protection for MARS and networkbased
IPSs and IDSs. The suggestions given are a good place to begin, but they by no means
work in every network. For example, the TCP and UDP ports described in the preceding
sections are only defaults. You can configure most of these services, which are common in
many networks, to use other ports. Check Point firewalls, for example, are commonly
configured to use different ports than the defaults of TCP ports 18184, 18190, and 18210.
INGRESS FIREWALL RULES
To simplify the work involved, you should define some network object groups on your
firewall. If you’re not familiar with this term, think of object groups as variables that you
can use while configuring the firewall to make life easier. Rather than referring to a large
list of IP addresses or TCP/UDP ports, you can simply refer to a name instead. The
following examples use an object group called CORP_NET, which consists of all IP
addresses used on your organization’s network.
Ingress traffic refers to traffic that is inbound to a firewall (toward CS-MARS) from a less
trusted network. Figure 4-1 shows both ingress traffic and egress traffic, or traffic that leaves
CS-MARS to go toward the less trusted network.
The following ingress rules are a good starting point for most companies:
Step 1 Permit syslog and SNMP trap traffic (UDP 162 and 514) from security
operations (SecOps).
Step 2 Permit NetFlow traffic (UDP 2049) from SecOps.
Step 3 Permit HTTPS (TCP 443) from SecOps if a large number of people will
be accessing the web console of MARS to run ad hoc reports. Otherwise,
permit HTTPS to a restricted range of addresses.
Step 4 Permit SSH (TCP 22) to a very restricted set of addresses. If the security
management network has its own VPN gateway, which might be a
function of the firewall, you might want to require administrators to
establish a VPN connection before permitting SSH.
Step 5 Permit HTTP (TCP 80) from any monitored web servers running iPlanet
or Apache. If you’re using NetCache appliances, permit HTTP from it as
well.
Step 6 If your MARS deployment consists of multiple MARS LCs that
communicate to a centralized MARS GC, permit required management
traffic between those systems (TCP 443 and 8444).
Step 7 Deny all other traffic.
EGRESS FIREWALL RULES
Egress firewall rules refer to filters that restrict traffic from the protected network to less
trusted networks. Ideal security would restrict outbound traffic to only those ports that are
necessary for proper functioning of the MARS appliance. However, in real life, this might
be unmanageable. You need to determine the proper balance between security and
manageability.
For example, a strict default egress policy might make sense for your company’s publicfacing
web server. Hopefully, connectivity from the Internet to your web server (ingress
rule) is permitted only on either TCP 80 or 443, depending on whether your web server uses
encrypted HTTP. The egress policy should deny all traffic that originates from the web
server to hosts on the Internet. In other words, someone should never be allowed to browse
the Internet from your web server, to download files from the web server, or to have other
communications from the web server to the Internet. By applying a proper egress rule on
the firewall that denies it, an attacker is also denied that same communications path. In most
instances where a web server, or any other server, is compromised by a hacker, the hacker’s
next steps include copying files to the web server. This is either to deface websites, install
root kits, or retrieve the software needed to further hack into the network. Strict egress
filters raise the difficulty level, often to a level that exceeds the capabilities of the hacker.
Depending on your environment and which MARS features you’re using, strict egress
filters might be unmanageable. However, you should evaluate them to see whether they are
workable in your environment.
The following list of egress filters serves as a good starter set for most networks:
Step 1 Permit traffic required for name resolution to CORP_NET—for
example, Domain Name System (DNS) and Server Message Block
(SMB) for Windows hosts (TCP and UDP 53, TCP 137 and 445) to
CORP_NET.
Step 2 Permit Network Time Protocol (NTP) to specified NTP servers, either on
your network or internetwork.
Step 3 Permit device discovery traffic on CORP_NET for routers and
switches—for example, Telnet (TCP 23), SSH (TCP 22), and SNMP
(UDP 161).
Step 4 Permit HTTPS to CORP_NET to allow MARS to discover Cisco
IDS/IPS sensors as well as to allow event retrieval from Cisco IDSs/IPSs
and Cisco routers running IOS IPS, and to allow communications
between MARS LCs and GCs. If possible, restrict this range to a subset
of CORP_NET.
Step 5 Permit FTP (TCP 21) to a centralized FTP server that contains
configuration files of routers and switches, if you want to take advantage
of this feature.
Step 6 Permit Simple Mail Transfer Protocol (SMTP) (TCP 25) to allow MARS
to e-mail reports and alerts to your SMTP gateway.
Step 7 Permit NFS (UDP 2049) if your MARS archive server resides on a
different network (not recommended).
Step 8 Permit TCP 8444 to allow communications between MARS LCs and
GCs, if they reside in different locations.
Step 9 Deny all other traffic.
If you want to take advantage of the MARS internal vulnerability assessment capabilities,
the preceding list of rules will not work. Instead, use the following egress filter list:
Step 1 Permit all TCP and UDP traffic sourced from CS-MARS or a third-party
vulnerability scanner.
Step 2 Permit NTP traffic to defined NTP servers, if they do not exist locally on
SecOps.
Step 3 Deny all other traffic.
In day-to-day use of MARS, when you choose to get more information about a specific
host, the internal vulnerability assessment feature of MARS initiates a port scan of the host.
You cannot accurately define an egress rule list that permits the vulnerability assessment to
take place while also restricting outbound ports. If you already use a supported third-party
vulnerability assessment tool, such as QualysGuard, you do not need to use the internal
tool. Otherwise, using the tool can greatly improve the accuracy of information presented
to you by MARS.
NETWORK-BASED IDS AND IPS ISSUES
A network-based IPS offers an additional level of protection to complement that provided
by a stateful inspection firewall. An IPS is closely related to an IDS. At first glance, the most
obvious difference between the two is how they are deployed.
An IDS examines copies of network traffic, looking for malicious traffic patterns. It then
identifies them and can sometimes be configured to take an automated response action, such
as resetting TCP connections or configuring another network device to block traffic from
an attacker.
NOTE:
It is important to remember that an IDS detects malicious traffic after it has already
happened. Although automated response actions can take place, it is usually too late to stop
the attack.
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As shown in Figure 4-2, an IDS is typically deployed beside a traffic flow. It receives copies
of network traffic from the network switches, hubs, taps, or routers. Because it does not sit
in the flow of traffic, it does not break anything that MARS requires.
An IDS often issues a large number of alerts based on traffic generated from MARS,
especially if you’re using the internal vulnerability assessment feature. You need to tune
your IDS so that it does not alert on the vulnerability scans that originate from MARS. You
might want to adjust the IDS tuning so that scans from MARS to your CORP_NET are
ignored, but scans directed to the Internet trigger an alert. It is generally considered a bad
practice to automatically scan hosts outside your own network; the practice might even be
illegal. Make sure that MARS is not configured to scan anything that is not on your own
network. Your firewall egress rules should not allow this either. However, in the case of a
misconfiguration, your IDS can alert the appropriate personnel so that the configuration
errors can be corrected.
An IPS sits in the path of network traffic (see Figure 4-3), usually as a transparent device
(like a bridge), and watches for many of the same behaviors as an IDS. A major difference
between the two, though, is the capability of the IPS to act instantly when malicious traffic
is seen.
NOTE:
In addition to the automated actions an IDS can take, an IPS can also prevent the malicious
traffic from passing through it.
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Because traffic must pass through an IPS, the IPS can prevent MARS from functioning
properly if it is misconfigured. Take time to closely watch alerts generated by your IPS and
tune it appropriately. Like the IDS, you should tune the IPS to allow vulnerability scanning
to occur from MARS to CORP_NET, while preventing it from scanning the Internet.
Some of the newest types of IPSs, such as the Cisco IPS, have a feature called traffic
normalization. This feature, in particular, causes the MARS vulnerability assessment to
fail. Traffic normalization enables several functions, including the following:
- Prevents illegal combinations of TCP flags from passing, or removes the illegal flags
- Prevents fragmented traffic from passing, or rebuilds it so that it is not fragmented
- Changes all packets in a traffic flow to have the same time to live (TTL)
This is just a small sampling of what a traffic normalizer does. In general, you can think of
it as an engine that takes traffic that does not conform to standards, and either prevents the
traffic from passing through the IPS or makes it conform to standards first.
By itself, traffic normalization breaks a large amount of attacks and reconnaissance
activities. It also stops vulnerability assessment tools from being able to accurately
determine information such as the operating system that a target host is running.
NOTE:
Cisco IPS 5.x and 6.x software, by default, does not generate alerts on most traffic
normalization signatures. To properly tune the software, you need to enable alerts on that
family of signatures.
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If you’re protecting your security management network with an IPS that supports traffic
normalization, you need to tune it to either ignore the scans from MARS and Qualys (or
other vulnerability scanners) or disable the traffic normalization capabilities.
SUMMARY
MARS contains sensitive information that you need to protect from malicious users. You
must protect MARS with a firewall that is properly configured to allow necessary inbound
and outbound traffic.
A network-based IDS or IPS can provide increased levels of security, but adds a level of
complexity.
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