Network Security
Attack Analysis
Outline
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Types of Attacks
Vulnerabilities Exploited
Network Attack Phases
Attack Detection Tools
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Top Cyber-security Risks
• Application vulnerabilities exceed OS vulnerabilities
– Password guessing – SQL, FTP, SSH
• Web application attacks
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–
–
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Server-side , client-side attacks
PHP remote file Include
Cross-site scripting
SQL injection
• Windows: Conficker/Downadup
• Apple: QuickTime …
• Zero Day Vulnerabilities
– File Format Vulnerabilities (pdf, Word, Execl, Flash, etc.)
www.sans.org – Top 20
Client-side Vulnerabilities in:
C1. Web Browsers
C2. Office Software
C3. Email Clients
C4. Media Players
Server-side Vulnerabilities in:
S1. Web Applications
S2. Windows Services
S3. Unix and Mac OS Services
S4. Backup Software
S5. Anti-virus Software
S6. Management Servers
S7. Database Software
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Security Policy and Personnel:
H1. Excessive User Rights and
Unauthorized Devices
H2. Phishing/Spear Phishing
H3. Unencrypted Laptops and
Removable Media
Application Abuse:
A1. Instant Messaging
A2. Peer-to-Peer Programs
Network Devices:
N1. VoIP Servers and Phones
Zero Day Attacks:
Z1. Zero Day Attacks
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Example Description
• C4 Media Players
– C4.1 Description
– C4.2 Operating Systems Affected
– C4.3 CVE Entries
– C4.4 How to determine if you are vulnerable
– C4.5 How to protect against MP
vulnerabilities
– C4.6 References
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C4.3 CVE Entries
• RealPlayer
CVE-2007-2497, CVE-2007-3410, CVE-2007-5601
• Apple iTunes
CVE-2007-3752
• Adobe Flash Player
CVE-2007-3457, CVE-2007-5476
• Apple Quicktime
CVE-2007-0462, CVE-2007-0588, CVE-2007-0466, CVE-20070711, CVE-2007-0712, CVE-2007-0714, CVE-2007-2175,CVE-20072295, CVE-2007-2296, CVE-2007-0754, CVE-2007-2388, CVE-20072389, CVE-2007-2392, CVE-2007-2393,CVE-2007-2394, CVE-20072396, CVE-2007-2397, CVE-2007-5045, CVE-2007-4673
• Windows Media Player
CVE-2006-6134, CVE-2007-3035, CVE-2007-3037, CVE-2007-5095
nvd.nist.gov
Types of Attacks
• Software vulnerabilities
– Buffer overflows
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Viruses, trojans, etc.
System or service configuration mistakes
Password weaknesses
Denial-of-Service attacks
Wireless Attacks
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Buffer Overflows
• Objective:
– Send more data to an application input than it
is designed to handle.
– Craft the data such that the overflow portion
will be interpreted as executable code.
– Typically done by getting data to overflow in
stack so that it overwrites PC address
• Depends on:
– Traditional (non-checked) data validation.
– Code instructions that do not validate input.
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Buffer Overflow Example
void function(char *str) {
char buffer[16];
strcpy(buffer,str);
}
void main() {
char large_string[256];
int i;
for( i = 0; i < 255; i++)
large_string[i] = 'A';
function(large_string);
}
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Stack Structure for function
bottom of
memory
code
<-----top of
stack
*str
ret
sfp
buffer
code
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top of
memory
buffer
sfp
ret
*str
[XXXXXXXXXXXXXXXX][XXXX][XXXX][XXXX]
bottom of
stack
pointer to char buffer (argument into function)
pointer to return address in main
saved frame pointer (reference into memory frame)
storage allocated for character array
…
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Stack Overflow
Before strcpy:
bottom of
memory
<------
top of
memory
buffer
sfp
ret
*str
[XXXXXXXXXXXXXXXX][1F3C][1F9A][1F7C]
top of
stack
bottom of
stack
After strcpy:
bottom of
memory
<-----top of
stack
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top of
memory
buffer
sfp
ret
*str
[AAAAAAAAAAAAAAAA][AAAA][AAAA][AAAA]
bottom of
stack
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Stack Manipulation
bottom of
memory
<-----top of
stack
top of
memory
buffer
sfp
ret
*str
[AAAAAAAAAAAAAAAA][XXXX][1F94][XXXX]
bottom of
stack
Overflow buffer with the bytes needed to
overwrite the return pointer with a desired address
That points to an instruction of your own crafting
bottom of
memory
<-----top of
stack
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top of
memory
buffer
sfp
ret
*str
[AAAAAAAAAAAAAAAA][XXXX][1F41][XXXX]
bottom of
stack
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Viruses, trojans, etc.
• Check for evidence of programs (and
versions) that are susceptible to attack.
• Test for outdated (or unchecked) virus
scan software.
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System or service configuration
mistakes
• Default passwords left in place
– Router passwords
– Program passwords
• Default (unused) services left running
– Sendmail
– Echo, time, etc.
• Default settings for firewalls and routers
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Password weaknesses
• Test for standard password weaknesses
– Short passwords
– Dictionary based passwords
– Personal information passwords (pets, family, etc.)
• Test for unencrypted passwords
• Try to download encrypted password files
– /etc/passwd, /etc/shadow
• Use dictionary, etc as source
– Encrypt word, compare to password file
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Wireless Attacks
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Scan for Access Points (War Driving)
Look for SSID beacons
Test for mac address blocking
Look for unencrypted access points
If encrypted, test for WEP / WPA
– If WEP, consider the value of capturing data
and trying to recover secret through IV
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Network Attack Phases
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•
•
•
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Reconnaissance
Vulnerability Identification
Penetration
Control
Embedding
Data extraction / modification
Attack Relay
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Reconnaissance
• Find out about network topology
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–
–
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What IP addresses are active?
What Operating Systems do they use?
What services / servers do they support?
What other machines do they talk to?
• Tools
– Port Scanners
– DNS queries (zone transfers)
• Defense
– Snort, Shadow
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Vulnerability Identification
• Once systems have been scanned,
specific sweeps are made to check for
specific service or system vulnerabilities
– See SANS top 20
– Buffer overflows, etc.
• Most Popular Targets
– Servers difficult to remove or relocate ( DNS,
mail, web, etc.)
• Defense
– Don’t expose vulnerabilities!
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Penetration
• Most sucessful hack is one that is not detected
– Second best is an attack that cannot be traced.
• Systems with some security typically rely on a
“hard shell”.
– Firewall or proxy servers
– Perhaps IDS
• If firewall is secure, then use the users
– Track external site visits
– Taint DNS records to point to an attack machine
– Let users establish the connection for you!
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Control
• Typically a bootsrtap process.
– Find an exploit that allows you to control a
process (program).
– Use that process to start up a process of your
choosing with permissions of the owner of the
original process
– This process will contact the attack host and
download the full exploit.
– Use that process to execute another exploit
that will get root privilege (if needed).
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Embedding
• Once into the system, the hacker will attempt to
hide several different access programs.
– If one exploit is discovered, perhaps others will not.
– Alter logging programs to not display packets
– Alter process display programs to not show
processes
– Etc.
• Want to be sure that the attack program (bot) will
survive a restart.
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Embedding
• Store exploits by overwriting little used existing
files (games,etc.)
• Store most of the exploit as fragments inside
other files (steganography), then use a small
reassembly program to rebuild on command
• Hide program on unused portions of the disk
• Load poritons of the bot onto unused eeprom on
the network card.
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Data extraction / modification
• First order of business is to send system data
back to relay
– Windows – registry
– Linux - /proc
• Transmit data slowly – over several different
sessions
• Encrypt and embed data into known (or
expected) data flows – www, ftp, e-mail, etc.
– Use existing programs RMON and arpwatch
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Attack Relay
• Use this new system as a relay to attack
other systems.
– Use multiple relays – ideally in multiple
countries – to link to attacked machines.
– Use multiple machines for an attack
• A few suspicious packets from a machine once in
a week may not be acted upon
• Multiple machines are harder to block.
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Attack Detection Tools
• Scanners
– Virus Scanners
– SpyBots
– Malware scanners
• IDS
– Network based
– Host based
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Profile of an Advanced
Cyber Intrusion
• Ongoing (since 1999) series of suspected
intrusions on US commercial and military
sites from PRC
• Information presented in an unclassified
document that details China’s capability to
conduct cyber attacks
• One element of that report is a detailed
report of an intrusion into a US commercial
network
Awareness of the Problem
• Information security staff at the company
became aware of the intrusion when they
detected large volumes of data leaving
their network
– Coming from multiple machines
– Going to multiple addresses mostly
(completely?) within the US
• Were able to implement blocks to stop the
flow, but an unknown volume of data was
transmitted.
Two Teams
• Able to distinguish teams based on the tools and
techniques used.
• Forensic Profile
– Able to distinguish individuals based on “keyboard behavior” –
tools, techniques, command combinations, elapsed time
between keyboard entries, etc.
• Breach Team
– Figure out how to get into the network and secure machines.
• Collection Team
– Determine what information to extract and implement the
extraction.
Data Compromised
• Information extracted was very carefully
selected.
– Files picked out of directories of related information
– Files generally were not opened pripr to extraction
• Suggests that intruders had very detailed
knowledge of the information in the network and
had been able to search through the files to
identify what they wanted.
– Took a lot of time
– Took detailed knowledge of the company
Activity prior to exfiltration
• Information Security (IS) detected low levels of
intrusive activity prior to exfiltration.
– Seemed to be folcused on maintenance of their
presence within the network
– When detected IS would block the link.
– Apparently intruders were able to open up other links
undetected to continue their reconaissance.
• Process continued for several days (at least).
Reconnaissance Phase
• Identify specific files, directories and file shares
that contained desirable information
• Identify specific users who would have access to
desired information and compromise their
accounts.
• Uncover and use password policies
• Identify group memberships
• Construct detailed network architecture
diagrams to facilitate information movement
• Process was very methodical and quiet.
Data Exfiltration Operation
Cmd /
Control
External Command and
Control (C2)
Compromised
users
Staging Sys via
RDP
Work
station
Staging
Work
station
Staging
File
Server
Staging
File
Server
Sending Hosts
(Internal)
Exfilt
Host
Collection Host
(External)
External
Host
Exfilt
Host
External
Host
File
Server
Exfilt
Host
External
Host
Analysis
• Used dozens of accounts over about 150
occasions to gather information.
– Very difficult to correlate the activities prior to
exfiltration.
• Group memberships were particularly
important in accessing data from noncompromised accounts.
Data Staging Process
• Took place over several days
• Noticed an increase in short duration communications
– Appeared to be used to verify resources, set up redundant
channels, etc.
• Transfer done in the evening (same time each night).
• Transfer desired data from file servers to mail servers.
– 75% of the company’s several dozen mail servers were involved
in the intrusion.
• Rename files to resemble legitimate Windows files on
mail servers.
• Encrypt and compress files into 650 MB RAR archives
Exfiltration
• Secure a compromised user machine for use as an internal
C2 station
• Move data into staging servers
• Test all staging servers by downloading a 20MB video file.
– Terminated download before complete.
• Identify local (US) external hosts to receive the data
• Used several versions of FTP (both standard and
customized versions) to get a working configuration for
offloading files.
• Finally got a working configuration to a US University site.
• Replicated the configuration 5 more times to increase
throughput.
• Eventually detected and blocked. IS noted repeated
attempts over the next 5 hours to regain access.
Summary
• There are many ways that hackers can get
into systems
• Complexity of systems today makes it
difficult to protect all possible attack
vectors.
• Several web sites available to identify
trends (SANS, etc.)
• Understand the process!
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References
• Stealth Coordinated Attack HOWTO
by Dragos Ruiu - 1999
– Google for a copy (it seems to move around)
• Network Intrusion Detection 3rd ed.- Northcutt and Novak
– New Riders Publishing 2003
• Maximum Linux Security – Anonymous
– Sams Publishing – 2000
• Ethical Hacking and Network Defense – Simpson
– Thomson Course Technonogy – 2006
• Smashing the Stack for Fun and Profit
– http://www.phrack.org/phrack/60/p60-0x06.txt
• PRC and Cyber Warfare
– http://www.uscc.gov/researchpapers/2009/NorthropGrumman_P
RC_Cyber_Paper_FINAL_Approved%20Report_16Oct2009.pdf
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