Denial-of-Service (DoS) Attack

Denial-of-Service

•Commonly used against information stores like web sites
•Simple and usually quite effective
•Does not pose a direct threat to sensitive data
•The attacker tries to prevent a service from being used and making that service unavailable to legitimate users
•Attackers typically go for high visibility targets such as the web server, or for infrastructure targets like routers and network links



Denial-of-Service Example
If a mail server is capable of receiving and delivering 10 messages a second, an attacker simply sends 20 messages per second. The legitimate traffic (as well as a lot of the malicious traffic) will get dropped, or the mail server might stop responding entirely.
-This type of an attack may be used as a diversion while another attack is made to actually compromise systems
-In addition, administrators are likely to make mistakes during an attack and possibly change a setting that creates a vulnerability that can be further exploited

Types of Denial-of-Service Attacks

• Buffer Overflow Attacks 
• SYN Flood Attack 
• Teardrop Attacks 
• Smurf Attack 
• DNS Attacks 
• Email Attacks 
• Physical Infrastructure Attacks
• Viruses/Worms

Buffer Overflow Attacks

The most common DoS attack sends more traffic to a device than the program anticipates that someone might send Buffer Overflow.

SYN Flood Attack

• When connection sessions are initiated between a client and server in a network, a very small space exists to handle the usually rapid "hand-shaking" exchange of messages that sets up a session. 
• The session-establishing packets include a SYN field that identifies the sequence order. 
• To cause this kind of attack, an attacker can send many packets, usually from a spoofed address, thus ensuring that no response is sent.

Teardrop Attack

• Exploits the way that the Internet Protocol (IP) requires a packet that is too large for the next router to handle be divided into fragments. 
• The fragmented packet identifies an offset to the beginning of the first packet that enables the entire packet to be reassembled by the receiving system. 
• In the teardrop attack, an attacker's IP puts a confusing value in the second or later fragment. If the receiving operating system cannot cope with such fragmentation, then it can cause the system to crash.

Smurf Attack

• The attacker sends an IP ping request to a network site.
• The ping packet requests that it be broadcast to a number of hosts within that local network. 
• The packet also indicates that the request is from a different site, i.e. the victim site that is to receive the denial of service. 
• This is called IP Spoofing--the victim site becomes the address of the originating packet. 
• The result is that lots of ping replies flood back to the victim host. If the flood is big enough then the victim host will no longer be able to receive or process "real" traffic.

DNS Attacks

• A famous DNS attack was a DDoS "ping" attack. The attackers broke into machines on the Internet (popularly called "zombies") and sent streams of forged packets at the 13 DNS root servers via intermediary legitimate machines. 
• The goal was to clog the servers, and communication links on the way to the servers, so that useful traffic was gridlocked. The assault is not DNS-specific--the same attack has been used against several popular Web servers in the last few years.

Email Attacks

• When using Microsoft Outlook, a script reads your address book and sends a copy of itself to everyone listed there, thus propagating itself around the Internet. 
• The script then modifies the computer’s registry so that the script runs itself again when restarted.

Physical Infrastructure Attacks

• Someone can just simply snip your cables! Fortunately this can be quickly noticed and dealt with. 
• Other physical infrastructure attacks can include recycling systems, affecting power to systems and actual destruction of computers or storage devices. 

Viruses/Worm

• Viruses or worms, which replicate across a network in various ways, can be viewed as denial-of-service attacks where the victim is not usually specifically targeted but simply a host unlucky enough to get the virus. 
• Available bandwidth can become saturated as the virus/worm attempts to replicate itself and find new victims

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Modern Network Security Threats

Major Concepts:
•Rationale for network security
•Data confidentiality, integrity, availability
•Risks, threats, vulnerabilities and countermeasures
•Methodology of a structured attack
•Security model (McCumber cube)
•Security policies, standards and guidelines
•Selecting and implementing countermeasures
•Network security design

What is Network Security?
National Security Telecommunications and Information Systems Security Committee (NSTISSC)
Network security is the protection of information and systems and hardware that use, store, and transmit that information.
Network security encompasses those steps that are taken to ensure the confidentiality, integrity, and availability of data or resources.

Rationale for Network Security
Network security initiatives and network security specialists can be found in private and public, large and small companies and organizations. The need for network security and its growth are driven by many factors:
1.Internet connectivity is 24/7 and is worldwide
2.Increase in cyber crime
3.Impact on business and individuals
4.Legislation & liabilities
5.Proliferation of threats
6.Sophistication of threats


Business Impact
1.Decrease in productivity
2.Loss of sales revenue
3.Release of unauthorized sensitive data
4.Threat of trade secrets or formulas
5.Compromise of reputation and trust
6.Loss of communications
7.Threat to environmental and safety systems
8.Loss of time

Goals of an Information
Security Program
•Confidentiality
-Prevent the disclosure of sensitive information from unauthorized people, resources, and processes
•Integrity
-The protection of system information or processes from intentional or accidental modification
•Availability
-The assurance that systems and data are
accessible by authorized users when needed


Risk Management
•Risk Analysis
•Threats
•Vulnerabilities
•Countermeasures


Risk Assessment

•Risk assessment involves determining the likelihood that the vulnerability is a risk to the organization
•Each vulnerability can be ranked by the scale
•Sometimes calculating anticipated losses can be helpful in determining the impact of a vulnerability



Asset Identification
•Categories of assets
       -Information Assets (people, hardware, software, systems)
       -Supporting Assets (facilities, utilities, services)
       -Critical Assets (can be either of those listed above)
•Attributes of the assets need to be compiled
•Determine each item’s relative value
       -How much revenue/profit does it generate?
       -What is the cost to replace it?
       -How difficult would it be to replace?
       -How quickly can it be replaced?




Types of Network Threats

•Impersonation
•Eavesdropping
•Denial-of-service
•Packet replay
•Man-in-the-middle
•Packet modification


Vulnerability

•A network vulnerability is a weakness in a system, technology, product or policy
•In today’s environment, several organizations track, organize and test these vulnerabilities
•The US government has a contract with an organization to track and publish network vulnerabilities
•Each vulnerability is given an ID and can be reviewed by network security professionals over the Internet.
•The common vulnerability exposure (CVE) list also publishes ways to prevent the vulnerability from being attacked

Vulnerability Appraisal
•It is very important that network security specialists comprehend the importance of vulnerability appraisal
•A vulnerability appraisal is a snapshot of the current security of the organization as it now stands
•What current security weaknesses may expose the assets to these threats?
•Vulnerability scanners are tools available as free Internet downloads and as commercial products
      -These tools compare the asset against a database of known vulnerabilities and produce a discovery                                        

          report that exposes the vulnerability and assesses its severity


Risk Management Terms
•Vulnerability – a system, network or device weakness
•Threat – potential danger posed by a vulnerability
•Threat agent – the entity that indentifies a vulnerability and uses it to attack the victim
•Risk – likelihood of a threat agent taking advantage of a vulnerability and the corresponding business impact
•Exposure – potential to experience losses from a threat agent
•Countermeasure – put into place to mitigate the potential risk


Types of Attacks


Structured attack

Come from hackers who are more highly motivated and technically competent. These people know system vulnerabilities and can understand and develop exploit code and scripts. They understand, develop, and use sophisticated hacking techniques to penetrate unsuspecting businesses. These groups are often involved with the major fraud and theft cases reported to law enforcement agencies.


Unstructured attack

Consists of mostly inexperienced individuals using easily available hacking tools such as shell scripts and password crackers. Even unstructured threats that are only executed with the intent of testing and challenging a hacker’s skills can still do serious damage to a company.


External attacks

Initiated by individuals or groups working outside of a company. They do not have authorized access to the computer systems or network. They gather information in order to work their way into a network mainly from the Internet or dialup access servers.


Internal attacks

More common and dangerous. Internal attacks are initiated by someone who has authorized access to the network. According to the FBI, internal access and misuse account for 60 to 80 percent of reported incidents. These attacks often are traced to disgruntled employees.

Passive Attack
-Listen to system passwords
-Release of message content
-Traffic analysis
-Data capturing 

Active Attack
-Attempt to log into someone else’s account
-Wire taps
-Denial of services
-Masquerading
-Message modifications

Specific Network Attacks

•ARP Attack
•Brute Force Attack
•Worms
•Flooding
•Sniffers
•Spoofing
•Redirected Attacks
•Tunneling Attack
•Covert Channels

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