The distributed denial
of service attacks during the week of February 7 highlighted security
weaknesses in hosts and software used in the Internet that put electronic
commerce at risk. These attacks also illuminated several recent trends and
served as a warning for the kinds of high-impact attacks that we may see in the
near future. This document outlines key trends and other factors that have
exacerbated these Internet security problems, summarizes near-term activities
that can be taken to help reduce the threat, and suggests research and
development directions that will be required to manage the emerging risks and
keep them within more tolerable bounds. For the problems described, activities are
listed for user organizations, Internet service providers, network
manufacturers, and system software providers.
Key Trends and Factors
The recent attacks
against e-commerce sites demonstrate the opportunities that attackers now have
because of several Internet trends and related factors:
Attack technology is
developing in an open-source environment and is evolving rapidly. Technology
producers, system administrators, and users are improving their ability to
react to emerging problems, but they are behind and significant damage to
systems and infrastructure can occur before effective defenses can be
implemented. As long as defensive strategies are reactionary, this situation
will worsen. Currently, there are tens of thousands – perhaps even millions – of
systems with weak security connected to the Internet. Attackers are (and will)
compromising these machines and building attack networks. Attack technology
takes advantage of the power of the Internet to exploit its own weaknesses and
software is being written by programmers who have no training in writing secure
code and are working in organizations that sacrifice the safety of their
clients for speed to market. This complex software is then being deployed in
security-critical environments and applications, to the detriment of all users.
User demand for new
software features instead of safety, coupled with industry response to that
demand, has resulted in software that is increasingly supportive of subversion,
computer viruses, data theft, and other malicious acts.
Because of the scope
and variety of the Internet, changing any particular piece of technology
usually cannot eliminate newly emerging problems; broad community action is
required. While point solutions can help dampen the effects of attacks, robust
solutions will come only with concentrated effort over several years.
The explosion in use
of the Internet is straining our scarce technical talent. The average level of
system administrator technical competence has decreased dramatically in the
last 5 years as non-technical people are pressed into service as system
administrators. Additionally, there has been little organized support of higher
education programs that can train and produce new scientists and educators with
meaningful experience and expertise in this emerging discipline.
The evolution of
attack technology and the deployment of attack tools transcend geography and
national boundaries. Solutions must be international in scope.
The difficulty of criminal
investigation of cybercrime coupled with the complexity of international law
mean that successful apprehension and prosecution of computer crime is
unlikely, and thus little deterrent value is realized.
The number of directly
connected homes, schools, libraries and other venues without trained system
administration and security staff is rapidly increasing. These “always-on,
rarely-protected” systems allow attackers to continue to add new systems
to their arsenal of captured weapons.
Immediate Steps to
Reduce Risk and Dampen the Effects of Attacks
There are several
steps that can be taken immediately by user organizations, Internet service
providers, network manufacturers, and system software providers to reduce risk
and decrease the impact of attacks. We hope that major users, including the
governments (around the world) will lead the user community by setting examples
– taking the necessary steps to protect their computers. And we hope that
industry and government will cooperate to educate the community of users –
about threats and potential courses of action – through public information
campaigns and technical education programs.
In all of these
recommendations, there may be instances where some steps are not feasible, but
these will be rare and requests for waivers within organizations should be
granted only on the basis of substantive proof validated by independent
Problem 1: Spoofing
Attackers often hide
the identity of machines used to carry out an attack by falsifying the source
address of the network communication. This makes it more difficult to identity
the sources of attack traffic and sometimes shifts attention onto innocent
third parties. Limiting the ability of an attacker to spoof IP source addresses
will not stop attacks, but will dramatically shorten the time needed to trace
an attack back to its origins.
User organizations and
Internet service providers can ensure that traffic exiting an organization’s
site, or entering an ISP’s network from a site, carries a source address
consistent with the set of addresses for that site. Although this would still
allow addresses to be spoofed within a site, it would allow tracing of attack
traffic to the site from which it emanated, substantially assisting in the
process of locating and isolating attacks traffic sources. Specifically user
organizations should ensure that all packets leaving their sites carry source
addresses within the address range of those sites. They should also ensure that
no traffic from “unroutable addresses” listed in RFC 1918 are sent
from their sites. This activity is often called egress filtering. User
organizations should take the lead in stopping this traffic because they have
the capacity on their routers to handle the load. ISPs can provide backup to
pick up spoofed traffic that is not caught by user filters. ISPs may also be
able to stop spoofing by accepting traffic (and passing it along) only if it
comes from authorized sources. This activity is often called ingress filtering.
Dial-up users are the
source of some attacks. Stopping spoofing by these users is also an important
step. ISPs, universities, libraries and others that serve dial-up users should
ensure that proper filters are in place to prevent dial-up connections from using
spoofed addresses. Network equipment vendors should ensure that no-IP-spoofing
is a user setting, and the default setting, on their dial-up equipment.
Problem 2: Broadcast
In a common attack,
the malicious user generates packets with a source address of the site he
wishes to attack (site A) (using spoofing as described in problem 1) and then
sends a series of network packets to an organization with lots of computers
(Site B), using an address that broadcasts the packets to every machine at site
B. Unless precautions have been taken, every machine at Site B will respond to
the packets and send data to the organization (Site A) that was the target of
the attack. The target will be flooded and people at Site A may blame the
people at Site B. Attacks of this type often are referred to as Smurf attacks.
In addition, the echo and chargen services can be used to create oscillation
attacks similar in effect to Smurf.
Unless an organization
is aware of a legitimate need to support broadcast or multicast traffic within
its environment, the forwarding of directed broadcasts should be turned off.
Even when broadcast applications are legitimate, an organization should block
certain types of traffic sent to “broadcast” addresses (e.g., ICMP Echo
Reply) messages so that its systems cannot be used to effect these Smurf
attacks. Network hardware vendors should ensure that routers can turn off the
forwarding of IP directed broadcast packets as described in RFC 2644 and that
this is the default configuration of every router.
Users should turn off
echo and chargen services unless they have a specific need for those services.
(This is good advice, in general, for all network services – they should be
disabled unless known to be needed.)
Problem 3: Lack of
Appropriate Response To Attacks
Many organizations do
not respond to complaints of attacks originating from their sites or to attacks
against their sites, or respond in a haphazard manner. This makes containment
and eradication of attacks difficult. Further, many organizations fail to share
information about attacks, giving the attacker community the advantage of
better intelligence sharing.
should establish incident response policies and teams with clearly defined
responsibilities and procedures. ISPs should establish methods of responding
quickly and staffing to support those methods when their systems are found to
have been used for attacks on other organizations.
should encourage system administrators to participate in industry-wide early
warning systems, where their corporate identities can be protected (if
necessary), to counter rapid dissemination of information among the attack
Attacks and system
flaws should be reported to appropriate authorities (e.g., vendors, response
teams) so that the information can be applied to defenses for other users.
Problem 4: Unprotected
Many computers are
vulnerable to take-over for distributed denial of service attacks because of
inadequate implementation of well-known “best practices.” When those
computers are used in attacks, the carelessness of their owners is instantly
converted to major costs, headaches, and embarrassment for the owners of
computers being attacked. Furthermore, once a computer has been compromised,
the data may be copied, altered or destroyed, programs changed, and the system
should check their systems periodically to determine whether they have had
malicious software installed, including DDOS Trojan Horse programs. If such
software is found, the system should be restored to a known good state.
should reduce the vulnerability of their systems by installing firewalls with
rule sets that tightly limit transmission across the site’s periphery (e.g.
deny traffic, both incoming and outgoing, unless given specific instructions to
All machines, routers,
and other Internet-accessible equipment should be periodically checked to
verify that all recommended security patches have been installed.
The security community
should maintain and publicize a current “Top-20 Exploited
vulnerabilities” and the “Top 20 Attacks” list of currently
most-often-exploited vulnerabilities to help system administrators set
Users should turn off
services that are not required and limit access to vulnerable management
services (e.g., RPC-based services).
Users and vendors
should cooperate to create “system-hardening” scripts that can be
used by less sophisticated users to close known holes and tighten settings to
make their systems more secure. Users should employ these tools when they are
vendors should ship systems where security defaults are set to the highest
level of security rather than the lowest level of security. These “secure
out-of –the-box” configurations will greatly aid novice users and system
administrators. They will furthermore save critically-scarce time for even the
most experienced security professionals.
should deploy “best practice” tools including firewalls (as described
above), intrusion detection systems, virus detection software, and software to
detect unauthorized changes to files. This will reduce the risk that systems
are compromised and used as a base for launching attacks. It will increase
confidence in the correct functioning of the systems. Use of software to detect
unauthorized changes may also be helpful in restoring compromised systems to
System and network
administrators should be given time and support for training and enhancement of
their skills. System administrators and auditors should be periodically certified
to verify that their security knowledge and skills are current.
Longer Term Efforts to
Provide Adequate Safeguards
The steps listed above
are needed now to allow us to begin to move away from the extremely vulnerable
state we are in. While these steps will help, they will not adequately reduce
the risk given the trends listed above. These trends hint at new security
requirements that will only be met if information technology and community
attitudes about the Internet are changed in fundamental ways. In addition,
research is needed in the areas of policy and law to enable us to deal with
aspects of the problem that technology improvements will not be able to address
by themselves. The following are some of the items that should be considered:
Establish load and
traffic volume monitoring at ISPs to provide early warning of attacks.
adoption of the IPsec components of Internet Protocol Version 6 and Secure
Domain Name System.
Increase the emphasis
on security in the research and development of Internet II.
development of tools that automatically generate router access control lists
for firewall and router policy.
development of software and hardware that is engineered for safety with
possibly vulnerable settings and services turned off, and encourage vendors to
automate security updating for their clients.
Sponsor research in
network protocols and infrastructure to implement real-time flow analysis and
adoption of routers and switches that can perform sophisticated filtering with
minimal performance degradation.
topological studies of the Internet to understand the nature of “choke
Test deployment and
continue research in anomaly-based, and other forms of intrusion detection.
consensus of uniform security policies to protect systems and to outline
security responsibilities of network operators, Internet service providers, and
and deployment of a secure communications infrastructure that can be used by
network operators and Internet service providers to enable real-time
collaboration when dealing with attacks.
Sponsor research and
development leading to safer operating systems that are also easier to maintain
Sponsor research into
survivable systems that are better able to resist, recognize, and recover from
attacks while still providing critical functionality.
Sponsor research into
better forensic tools and methods to trace and apprehend malicious users
without forcing the adoption of privacy-invading monitoring.
infrastructure support for centers of excellence in information security
education and research to produce a new generation of leaders in the field.
Consider changes in
government procurement policy to emphasize security and safety rather than
simply cost when acquiring information systems, and to hold managers
accountable for poor security.