Download Computer Security Incident Handling Guide (Chapters 4, 5, 6 and 8

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A denial of service (DoS) is an action that prevents or
impairs the authorized use of networks, systems, or
applications by exhausting resources such as central
processing units, memory, bandwidth, or disk space.
Examples:
› Using all available network bandwidth by generating
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unusually large volumes of traffic
Sending malformed TCP/IP packets to a server so that its
operating system will crash
Sending illegal requests to an application to crash it
Making many processor-intensive requests so that the
server’s processing resources are full
Consuming all available disk space by creating many
large files
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Network bandwidth is so large for most
organizations that a single attacking machine
cannot cause a network DoS.
DDoS attacks coordinate an attack among
many computers
Lack of availability of computing and network
services causes significant disruption an major
financial lost
Two types of components:
› Agents: which run on compromised hosts and
perform the actual attacks (bots)
› Handler: which is a program that controls the agents,
telling them when, what, and how to attack.
Reflector
Attacks
• A host sends many requests with a spoofed source address to a
service on an intermediate host
• The host generates a reply to each request and sends these replies
to the spoofed address
• Examples of reflector services: echo, chargen, DNS, SNMP, ISAKMP
Amplifier
Attacks
• Involves sending requests (such as ICMP or UDP) with a spoofed
source address to an expected broadcast address hoping that
many hosts will receive and it and respond to it.
• Example: DNS recursion attack
Flood
Attacks
• Makes a resource unavailable by initiating large numbers of
incomplete connection requests. Overwhelms the capacity and
prevents new connections from being made.
• Examples: Peer-to-peer attack, synflood attack
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Talk with the organizations ISPs about how they
handle network-based DoS attacks
› Filtering or limiting traffic, blocking a particular source
IP address or ICMP messages, providing logs,
retracing attacks to their source
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Consider participating in a coordinated
response to a widespread DDoS attack that
affects many organizations
› Exchange information regarding such an attack with
a centralized incident response entity
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Deploy and configure intrusion detection and
prevention software to prevent DoS traffic
› Network behavior analysis software can identify
unusual traffic flows
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Perform ongoing resource monitoring to
establish baselines of network bandwidth
utilization
Internet Health Monitoring: when a networkbased DoS occurs, incident responders could
use Web sites to attempt to determine if similar
attacks are currently affecting other
organizations
Meet with network infrastructure administrators
› Adjust logging of a certain type of activity
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Maintain local copies of any information that
may be useful in handling DoS incidents
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Configure the network perimeter to deny all incoming and
outgoing traffic that is not explicitly permitted
Block services that are used in DoS attacks (ex. Echo)
Perform egress and ingress filtering to block spoofed packets
Block traffic from unassigned IP address ranges
Make certain firewall rules and router ACL’s are written and
sequenced properly
› Limit incoming and outgoing ICMP traffic
› Block outgoing connections to common IRC, P2P services if the
usage is not permitted.
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Implement Rate limiting for certain protocols (ex. ICMP)
 Disable unneeded services
 Ensure that networks and systems are not running near
max. capacity so minor DoS attacks can’t occur easily.
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Precursors:
› DoS attacks are often
preceded by
reconnaissance
activity – a low
volume of the traffic
that will be used in
the actual attack - to
determine which
attacks may be
effective
› A newly released DoS
tool
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Responses:
› Example: Alter firewall
rulesets to block a
particular protocol
from being used
› Investigate the new
tool and alter security
controls accordingly
Network-based DoS
against a particular host
Network-based DoS
against a network
•User reports of system
unavailability
•Unexplained
connection losses
•Increased Network
bandwidth utilization
•Large number of
connections to a single
host
•Asymmetric network
traffic pattern
•Firewall and router log
entries
•Packets with unusual
source addressed
•Packets with
nonexistent destination
addresses
•Network Intrusion
detection alerts
•User reports of system
and network
unavailablity
DoS against the
operating system or
application of a
particular host
•User reports of system
and application
unavailability
•Operating system log
entries
•Network and host
intrusion detection
alerts
•Packets with unusual
source addresses
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Correct the vulnerability or weakness that is
being exploited
› Patch the OS
› Block unnecessary services
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Implement filtering based on the
characteristic of the attack
› Temporarily block certain requests (ICMP)
› Rate limiting
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Have the ISP implement filtering
Relocate the target
Attack the attackers (not recommended)
Identify the source of the attack from
observed traffic (very difficult)
 Trace attacks back through ISPs (easier if
attack is ongoing)
 Review Log Entries (Some may be
overwritten depending on logging
practices)
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Configure firewall rulesets to prevent reflector
attacks
› Reject suspicious combinations of source and
destination ports
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Configure border routers to prevent amplifier
attacks
› Do not forward directed broadcasts
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Determine how ISP can assist
Configure security software
Perimeter security – deny all incoming and
outgoing traffic not expressly permitted
Create a containment strategy that includes
several solutions in sequence
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Viruses – designed to self-replicated
› Compiled viruses: executed by the operating
system
 File Infector viruses: Attach themselves to an
executable program
 Boot Sector viruses: Infects the master boot record
of a hard drive or removable media
› Interpreted viruses: executed by an application
(most common)
 Macro viruses: Attach themselves to application
documents
 Script viruses: Similar to a macro but written in a
language understood by the OS
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Worms – self-replicating programs that are completely selfcontained.
Network Service Worms: spread by exploiting a vulnerability in a network
service associated with an OS or an application
› Mass Mailing Worms: Similar to email-borne viruses but are self-contained
instead of infecting an existing file.
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Trojan Horses – non-replicating programs that appear to be benign
but actually have a hidden malicious purpose
 Others:
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Malicious Mobile Code
Blended Attack (Ex: Nimda worm)
Tracking Cookies
Attacker Tools:
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Backdoors
Keystroke Loggers
Rootkits
Web browser plug-ins
Non-Malware Threats:
 Social Engineering
 Phishing
 Virus Hoaxes
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Use Antivirus Software
Prevent the installation of Spyware
Block suspicious files
Filtering Spam
Limit the use of nonessential programs with file
transfer capabilities (IM, P2P,etc.)
Educate users about email attachments
Eliminate Open Window Shares
Use Web Browser Security to Limit Mobile Code
Prevent open relaying of email
Configure email clients to act more securely
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Precursor:
› An alert warns of new
malicious code that
targets software the
organization uses
› Antivirus software
detects and disinfects
or quarantines
infected file
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Response
› Research new virus,
Update antivirus
software, configure
email clients to block
emails with certain
characteristics
› Determine how it
entered the system
and what vulnerability
it was attempting to
exploit
A virus that spreads
through email infects
a host
• Antivirus software alerts of infected files
• Sudden increase in the number of emails being sent and received
• Deleted, corrupted, or inaccessible files
• System instability and crashed
Malicious mobile
code on a Web site
exploits vulnerabilities
on a host
• Unexpected dialog boxes, requesting permission to do something
• Unusual graphics, such as overlapping or overlaid message boxes
• Network connections between the host and some unknown system
• Sudden increase in the number of emails being sent and received
A user receives a
virus hoax message
• Original source of the message is not an authoritative computer
security group, but a government agency or an official person.
• No links to outside sources
• Tone and terminology attempt to invoke panic or sense of urgency
• Urges recipients to delete certain files and forward the message on
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Identifying and Isolating other infected hosts
› Performing port scans
› Use antivirus scanning and cleaning tools
› Review logs
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Send unknown malicious code to antivirus
vendors
Configuring email servers and clients to block
emails
Blocking particular hosts
Shutting down email servers
Isolate networks from the internet
Disabling services, possibly connectivity
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Forensic Identification
› Antivirus software, spyware detection, content
filtering
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Active Identification
› Used to identify which hosts are currently
infected
› Deploying patches, updates, running a
disinfection utility
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Manual Identification
› Most labor-intensive
› IT staff identify infections by using information on
the malware and the signs of an infection
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Make users aware of malicious code issues
– Education!!
Read antivirus bulletins
Use antivirus software and update regularly
Configure software to block suspicious files
Eliminate open window shares
Contain malicious code incidents as fast as
possible
Deploy host-based intrusion detection and
prevention systems
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An unauthorized access incident occurs when
a person gains access to resources that the
person was not intended to have. It is typically
gained through the exploitation of operating
system or application vulnerabilities, the
acquisition of usernames and passwords, or
social engineering.
Examples:
› Guessing or cracking passwords
› Viewing or copying sensitive data
› Running a packet sniffer on a workstation to capture
usernames and passwords
› Using an unattended, logged-in workstation without
permission
Network
Security
• Put all publicly accessible services on secured DMZ network
segments
• Use private IP addresses for all hosts on internal networks
• Perform regular vulnerability assessments to identify serious risks
• Run services with least privileges
Host Security • Require hosts to lock idle screens automatically
Authentication
and
Authorization
• Create a good password policy
• Require sufficiently strong authentication
• Implement Physical Security
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Precursors:
› Users report possible social engineering
attacks
 Response: Give advice to all users on how to
handle social engineering attempts
› A person or system may observe a failed
physical access attempt
 Response: Detain the person. Strengthen
physical and computer security controls if
necessary
Root compromise
of a host
• Unusual traffic to
and from the host
• System
configuration
changes
• Modification of
critical files
• Unexplained
account usage
• New files or
directories with
unusual names
Physical Intruder
Unauthorized data
modification
• User reports of
network or system
unavailability
• System status
changes
• Hardware is
completely or
partially missing
• Unauthorized
new hardware
• Ex: Defacing web
server
• Increased
resource
utilization
• User reports of
data
modification
• Modifications to
critical files
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Isolate the affected systems
› Perform port scans for backdoors
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Disable the affected service
Eliminate the attacker’s route into the
environment
Disable user accounts that may have been
compromised
Enhance physical security measures
When unauthorized access is suspected,
make a full image backup of the system
A multiple component incident is a single
incident that encompasses two or more
incidents
 Example:
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› Malicious code spread through email
compromises an internal workstation
› An attacker uses the infected workstation to
compromise additional workstations and servers
› An attacker uses one of the compromised hosts
to launch a DDoS attack against another
organization
Preparation,
Detection, &
Analysis
Containment,
Eradication, &
Recovery
Conduct exercises in
which the incident
response team reviews
scenarios of multiple
component incidents
Better to contain the
initial incident and
then search for signs of
other components &
then handle the most
urgent need first
Difficult to assess
because components
may or may not be
related, incidents may
not be known
Unauthorized access
incidents most likely
have multiple
components