COEN 152/252 Computer Forensics

COEN 152/252Computer Forensics

Data Analysis Techniques for

Hard Drives

Data Analysis Techniques

Create forensic duplicate. Protect original as best evidence.

Review image file (with tools).

Report. Testify. (via declaration or in-person)


Need collaboration between forensics investigators and attorneys, paralegals and witnesses.


Sources of Evidence Existing Files Deleted Files Logs Special system files (registry, cron) Email archives, printer spools Administrative settings


File restoration techniques FAT, NTFS

By hand with a hexeditor Specialty tools like Norton undelete Forensics software like EnCase, FTK Mount drive on UNIX system and

use UNIX tools (Fatback)

Data Analysis Techniques Unix system

With a hex editor edit the link count in inodes, file will then be linked to Lost&Found

debugfs to relink a file to Lost&Found in ext2


Deleted files are overwritten if Drive is wiped (e.g. part of PGP suite) New files are created on the partition New software is installed on the

partition Applications running may update the

partition


Deleted files are overwritten if The partition stores the %systemroot%

directory and Windows modifies it for internal housekeeping.

If the partition contains the web browser cache

If the volume contains the TEMP directory Pagefile.sys Hiberfil.sys


Deleted files are overwritten At system shutdown / startup


Free, slack and unallocated space Use a hex-editor Use a specialty tool that generates a

file by appending all slack and free space

Use a forensics tool

Free: Outside of a partition.Slack: Allocated, but unused overhang in the last cluster of a fileUnallocated: Not assigned to a current file.


First Task: Generate database of all files

Full path. MAC-dates & -times. Logical size of file. MD5 hash (to counteract evidence

deterioration).


Generate database of all files Use MD5 hash to exclude well-known

files from investigation.


Prepare drive for string searches. Forensics tools do this automatically. Need to deal with proprietary formats. Compressed files need to be

uncompressed. Encrypted files need to be

unencrypted.


Perform string searches On UNIX, use grep. Forensics tools preprocess forensic

duplicates.


Perform String Searches The “How” is easier than the “What”. Investigator and analyst need to work

together: “What are we looking for?” “What information do we need?”


Example:The hard drive of a robbery suspect contains

numerous references to his “little excursions”.

To tie the suspect to the computer, establish usage by suspect alone by: Finding personal pictures (look for jpg). Restore old emails. Restore chat sessions.

http://www.signonsandiego.com/news/metro/santana/20010312-9999_1n12compute.html

Data Analysis TechniquesWhat to look for

Email Primary Source of Evidence. Email in transit is protected by the

EPCA and other statutes. Checking email after transition is

treated similar to searches of files.


Print Spooler Files. Typically deleted right after printing. Might not be overwritten.


Web Cache Evidence All web browsers cache. Some delete files after session closes.

Ex.: United States v. Tucker: The government introduced Internet conversations taken from Tucker's

computer which showed that while he was looking for pictures he stated that he was into "young action" and would "like to start trading (3)27" and introduced a listing of Internet conversations documenting Tucker's trading of such images.

United States Court of Appeals, Eleventh Circuit.No. 97-2767


Swap Files / Virtual Memory Files Can be very large. Use Forensics Tools like Encase Alternatively: Hex Editors, Norton

Disk Commander (under Windows)

Windows Data Analysis Perform keyword searches. Review Logs. Review Registry. Review swap files. Review special application files:

Internet Cache Recycle Bin Printer Spool Email Files

Windows Data Analysis: Text Searches

Raw Data Level BinText (Foundstone) Disk Investigator (K. Soloway) SectorSpyXP (McCamy, Lexun

Freeware) Forensics Tools

Encase FTK Mareswares

Windows Data Analysis: Text Searches

Windows Data AnalysisLogs

Windows NT, 2000, XP maintain log files

System Log Application Log Security Log


Live System:

Use Event Viewer

Windows Data AnalysisLogs Event Viewer Event Viewer


Event Log Dump Use PsLogList (sysinternal) dumpel (Win2000 Resource Kit)


From forensics duplicate secevent.evt appevent.evt sysevent.evt


Drawbacks Default security logging is “no

logging”. Do not record IP addresses Application log uses localized

settings.(Forensics workstation will not interpret

these.)

Windows Data AnalysisLogsInternet Information Services (IIS) has its

own set of logs. Uses W3C standards as a default


Need to be enabled. More important for incidence

response than for law enforcement.

Get HTTP status codes.


Many other applications log: Internal firewalls.

Create your own log from the timestamp of files around critical times. FileList (www.forensics-intl.com) will

do this for you.

Windows Data AnalysisReviewing Relevant Files

Recycle Bin Folder Recycled in Win95/98. Folder Recycler in WinNT/2000/XP.

Date and Time of Deletion in System file INFO in Win95 System file INFO2 in Win98

Information available in Win2000, WinXP


Windows moves deleted file into the recycle bin.

It deletes from there. Thus, files can be retrieved from

deleted recycle bin entries.


$Logfile entry in the MFT contains the log of all file system transactions

Deletion of a file leaves several entries in $Logfile

Not unusual to find files that are no longer on the disk

Shows that file was used by the system


Shortcuts can contain relevant information.

Stored in the desktop folder.

A special agent of the Illinois Attorney General’s Office investigated a case involving child pornography. The agent located a shortcut file in the Windows/Desktop folder whose target was a screensaver program. Upon examining the screensaver program, the agent found that it caused 30 images depicting child pornography to be displayed on the computer’s monitor when the shortcut was activated. Casey, p. 153


Thumbs.db (System file) Contains thumbs pictures for folder. Not perfectly synchronized with

folder. Deleted images might still be

available.


Temporary files Files with extension tmp Created by many applications

Emails with large attachments: Attachments are probably stored as

temp files. (Depends on email system.)

Look for file extensions .tmp .


Internet Explorer (as well as other browsers) use a cache.

index.dat contains internet explorer cached websites.

Written in binary. Use Pasco from Foundstone.




Browser Cache C:\Documents and Settings\

Username\ Local Settings\Temporary Internet Files

Or C:\Program Files\Netscape\Users\

Username\Cache


Windows Data AnalysisReviewing Relevant Files Cookies can be partially decyphered. Use galleta from foundstone.


Typically, concatenate all cookies. Redirect galleta into an excel file. Investigate the excel file.

Windows Data AnalysisReviewing Relevant Files Dial-up Networking

rasautou –s gives autodial addresses

Windows Data AnalysisRegistry

Database that stores settings and options for 32b MSWin OS

Contains information and setting for Hardware Software Users Preferences


Win95, Win98 USER.DAT, SYSTEM.DAT in WindowsWinME USER.DAT, SYSTEM.DAT, CLASSES.DATWinNT, 2000, XP In %SystemRoot%\System32\Config

Windows Data AnalysisRegistry Use RegEdit to access.

Before experimentation, make a backup of the registry.


Hierarchical structure Main branches are Hives Hives contain keys. Keys can contain subkeys and

values


Windows Data AnalysisRegistry Six main branches

HKEY_CLASSES_ROOT - This branch contains all of your file association mappings to support the drag-and-drop feature, OLE information, Windows shortcuts, and core aspects of the Windows user interface.

HKEY_CURRENT_USER - This branch links to the section of HKEY_USERS appropriate for the user currently logged onto the PC and contains information such as logon names, desktop settings, and Start menu settings.


HKEY_LOCAL_MACHINE - This branch contains computer specific information about the type of hardware, software, and other preferences on a given PC, this information is used for all users who log onto this computer.

HKEY_USERS - This branch contains individual preferences for each user of the computer, each user is represented by a SID sub-key located under the main branch.


HKEY_CURRENT_CONFIG - links to the section of HKEY_LOCAL_MACHINE appropriate for the current hardware configuration.

HKEY_DYN_DATA - points to the part of HKEY_LOCAL_MACHINE, for use with the Plug-&-Play features of Windows, this section is dynamic and will change as devices are added and removed from the system.


Registry Editor can import and export registry settings to / from a text file.

Copy registry hive files from the forensic duplicate to your forensic work station.

Import them into regedit.

IF YOU MESS UP THE REGISTRY, YOU NEED TO REBUILD YOUR SYSTEM.

Windows Data AnalysisRegistry In a recent investigation by the Los Angeles County

Sheriff’s Computer Crime Unit, a detective investigated an employee suspected of misappropriating confidential computer information stored by his company. When the detective examined one of the workplace computers, he found remnants of a key-trapping program in the registry. During an interview, the suspect admitted to having installed, used, and deleted the key-trapping program for the purposes of obtaining user names and passwords of coworkers.



Use the registry to Find installed software (such as

L0phtcrack). http://www.l0phtcrack.com/learn.html

Manually deleted software. Use backups of the registry to trace

the installation and uninstallation of software.

Find data on user accounts


Use the registry to obtain listing of applications that are

set to run automatically obtain registry entries that have been

modified lately Registry keys have LastWrite time

64b value representing 100 nanoseconds since January 1, 1601.

User accounts

Windows Data AnalysisMS Word files

Word documents contain a revision log. Used by Richard M. Smith to investigate a

press release by PM Blair. Turned out that press release was mainly a

copy of an Middle East Review of International Affairs article.

.pdf, .html, … files generated from .doc files do not have this revision history.

Windows Data Analysis.pfd files

.pdf files also contain meta-data Accessible in Adobe

Reader

Windows Data AnalysisUnusual or Hidden Files NTSF uses a feature from Mac Hierarchical

File System to store multiple entry under one file entry. “Data Streams”

Allow us to hide a file copy nc.exe logo.jpg:nc.exe

Now nc.exe is hidden. Use SFind (foundstone) to find streamed

files. http://www.securityfocus.com/infocus/182

2 Excellent article on the use of ADS as a compromise tool.

Windows Data Analysis Print Spooler Files

Print Spooler Files. (EMF under Win). EMF files are deleted after printing.

“Gap-Toothed Bandit”, Micheal Craig Dickman, used proceeds from bank robberies to support his struggling biotech start-up.

Arrested after a heist in La Jolla, 1999. SD RCFL found the demand notes as a deleted

EMF file on his laptop.

Data Analysis TechniquesWhat to look for Print Spooling uses temporary files.

contain data to be printed. data on the print job.

Two methods, RAW and EMF Shadow file .SHD info on print job

settings .SPL contains data to be printed (RAW) .SPL contains file name, method, list of

files with print data EMF****.TMPRef: [MS-EMFSPOOL]: Enhanced Metafile Spool Format Specification

[MS-EMF]: Enhanced Metafile Format Specification


Department of Consumer Affairs in Orange County, CA, arrested a suspect for selling counterfeit state license certificates and seized his computer. Although the examiners had seized some of the counterfeit certificates from victims, they were unable to locate evidence on the computer. When the examiners requested a second review from the California Department of Insurance, Fraud Division, the Computer Forensics Team identified several deleted enhanced metafiles that exactly matched the paper copies that had been seized during the investigation. The only evidence present on the drive were the enhanced metafiles. The defendant was convicted at trial. Casey, p. 163

Windows Data AnalysisRogue Processes

To find rogue processes on a duplicate image

Restore the file system. Run a virus software. Disable writing to restored volume.

Windows Data AnalysisFind Hidden Doors

Schedule an event

remote /s “cmd.exe” mysystem Remote command from NT Resource Kit

remote /c “cmd.exe” mysystem Allows to connect with a command

prompt from outside the system Schedule this with the at or the soon

utility

Windows Data AnalysisFind Hidden Doors ‘at’ will find any jobs that

have been scheduled:

Windows Data AnalysisReview last searches

Use AFind (foundstone) to look for the last few files accessed.

Look at the Find scrollbox. Registry entry at:

Windows Data AnalysisReview last searches

Windows Data AnalysisReview Most Recently Used Windows Registry MRU subkeys

Windows Data AnalysisReview Most Recently Used Windows Registry MRU subkeys

UNIX Data Analysis Review all pertinent logs Perform keyword searches Review relevant files Identify unauthorized user accounts or

groups Identify rogue processes Check for unauthorized access points Analyze trust relationships Check for kernel module rootkits

Unix Data AnalysisLogs Unix maintains a variety of logs. A hacker could change the logs. But you need to look at them. Placed in directories depending on

UNIX flavor /var/log usr/adm Var/adm

UNIX Data AnalysisLogs

syslog Controlled by /etc/syslog.conf Uses syslogd Can be used to log remotely

Unix Data AnalysisLogs

Look at the syslog.conf Three fields:

Facility field: subsystem that produced the log (e.g. mail)

Priority field: debug, info, notice, warning, err, crit, alert, emerg

Action field: how is the log recorded, typically name of log field (or IP address)


Log entries In ASCII Usually world-readable Only writable by root


Remote Syslog Server logs Attackers with root privileges can

change the logs Use a remote syslog server for

safety Attacker can add spurious entries to

the remote syslog Harden remote syslog server


TCP Wrappers Host based access control for TCP

and UDP services Any connection attempt are logged

via syslogMay 13 23:11:45 victim sshd[12528]:

ROOT LOGIN REFUSED FROM www.scu.edu

May 13 23:19:03 victim in.tftpd[524]: connect from 10.10.10.10


Other network logs Server specific logs, e.g. for FTP,

Apache, SSH ……

Unix Data AnalysisHost Logging

su command logs Part of syslog Stored in var/log/messages

Currently logged in users Stored in utmp or wtmp Use w, who, finger, last to read Modified by many hacker tools


Logon attempt logs Recorded on most UNIX machines /var/messages in LINUX


cron Allows users to schedule programs

for future execution Often used for attacks Logged, typically in /var/cron/log

Unix Data AnalysisUser Activity Logging

Every command by every user can be logged

Shells store history files for each user

Unix Data AnalysisLogging

Attacker gains root access to system Deletes .bash-history file Links file to /dev/null Can no longer log

Look for the shell log:[linuxbox] # ls –altotal 52drwxr-x--- 5 root root 4096 Dec 12 04:47 .drwxr-x--- 5 root root 4096 Dec 8 01:27 ..-rw------- 1 root root 108 Dec 12 04:47

.XAuthority-rw-r--r-- 1 root root 1198 Aug 23 04:47 .XDefaultslrwxrwxrwx 1 root tty 9 Dec 8 14:12.bash_history -

> /dev/null

UNIX Data AnalysisString Searches

grep String search within a file String search within a binary file Recursive searches

# grep root /etc/passwd

root:x:0:0:root: /root: /bin/bash

# grep PROMIC /sbin/ifconfig

Binary file /sbin/ifconfig matches

# grep –r –I password /

UNIX Data AnalysisString Searches

find Use to search for a file by name E.g., find “…” (a typical hacker trick to

hide a file)

Found one.

# find / -name “\.\.\.” –print

/home/hacker/MDAc/temp/…/root/…

UNIX Data AnalysisRelevant Files

Finding relevant files after an incident is an art.

Careful about destroying evidence by running system commands that will change times.

Mount evidence drive read-only or better, duplicate.

UNIX Data AnalysisRelevant Files

Identify the time of the incident. Look for files accessed, created or

modified around that time. Use find with –atime, -ctime, -

mtime option

UNIX Data AnalysisRelevant Files: SUID Programs

UNIX allows applications to set the user-id (SUID) and set the group-id (SGID).

Programs run with privileges of owner, typically root.

Programs are source of most privilege escalation attacks.


Sometimes unprivileged users need to accomplish tasks that require high privileges.

For example, passwd needs to access the password file in /etc/passwd

But users should not be given access to /etc/passwd


User invokes passwd passwd changes its UID (with

SUID) passwd now runs with root UID passwd can now access the

password file.


You recognize these programs with ls –l

File permission have an s instead of an x

-rwsr-xr-- SUID program -rwxr-sr-- SGID program


SECURITY INCIDENT EXAMPLE Superuser is logged on as root and

leaves terminal unattended

Creates SUID shell. Anyone invoking /tmp/break-account

gets root privileges.

# cp /bin/sh /tmp/break-acct

#chmod 4755 /tmp/break-acct


Old Break-in /usr/lib/preserve is used by vi and

ex editors to make an automatic backup of a file that is edited when the users suddenly disconnects.

preserve writes file changes to a temp file in a special directory


preserve uses /bin/mail to send the user a notification that the file has been saved.

This temp file should not be accessible by world.

Thus, preserve needs root privileges


preserve was installed as SUID root. preserve ran /bin/mail as root. preserve executed the mail

program with the system function call.

system uses sh to parse the string that it executes.


Problem: Shell variable IFS tells sh how to

interpret the white spaces. Normally sets white spaces to be

space, tab, enter, etc. Attacker sets white spaces to

“/”


Attacker runs vi. Attacker crashes system. preserve runs. system interprets /bin/mail as “bin

mail” Thus, it executes any program

called bin with argument mail as root.


Find all SUID SGID with the following command:

find starts in / Looks for files with permission

002000 (SGID) or 004000 (SUID) Know what to expect.

# find / $ -perm -00400 –o –perm -002000 $ –type f -print

UNIX Data AnalysisRelevant Files: Hidden Files

Hide “bad” files By giving them innocuous names By giving a name similar to a

reasonable name “ syslog” vs. “syslog”

Calling a directory “…” (“.” current directory, “..” parent directory)

UNIX Data AnalysisRelevant Files: Configuration Files

Primary target to keep access for a hacker.

etc/hosts.allow etc/hosts.deny determine access policy.

/etc/inetd.conf controls network services

UNIX Data AnalysisRelevant Files: Configuration Files

Add an entry to inetd.conf:

Simple backdoor that listens on port 55000

Same telnet server as the one for port 23.

Port 55000 might not be monitored

telnet2 stream tcp nowait root /usr/sbin/tcpd in.telnetd

UNIX Data AnalysisRelevant Files: cron

cron facility used to schedule future executions of programs

/var/spool/cron /usr/spool/cron stores cron jobs

/etc/rc.d contains a listing of programs that start when UNIX boots.

Check all startup scripts for trojans.

UNIX Data AnalysisPhone Home

Outgoing traffic is usually not monitored.

Compromised system uses cron to initiate a connection to an outside system.

Outside system can control the compromised system.

UNIX Data AnalysisRelevant Files: Startup

User home directory contain startup files.

.login .profile .cshrc

UNIX Data AnalysisRelevant Files: /tmp

Only world-writable file system on a typical UNIX system.

Hangout for nefarious tools.

UNIX Data AnalysisUser Accounts

Each user has an entry in /etc/passwddvader:x:512:516:Darth

Vader:/home/dvader:/bin/bash User name Password (shadowed) User Id Group Id Comment field Home directory Default login shell


/etc/groups defines groups:root::0:root, tschwarzbin::2:root,bin,daemonsys::3:root,bin,sys,admadm::4:root,adm,daemonuucp::5:root,uucp

User names


If suspicious of compromise, investigate user accounts and group accounts.

UNIX Data AnalysisChecking for Unauthorized Access Points

Investigate all network services for potential access points.

X-server FTP Telnet DNS Sendmail

finger SNMP IMAP POP HTTP HTTPS

UNIX Data AnalysisAnalyzing Trust Relationships If machine A trusts machine B,

then anyone on machine B can access services on machine A.

Don’t set up trust relationships. They allow an attacker to escalate

privileges to other machines Check files such as

/etc/hosts.equiv or .rhosts

UNIX Data AnalysisAnalyzing Trust Relationships

Network topology routes data through other computers.

Sniffing (esp. for passwords). Even possible in a switched

environment: arpredirect in dsniff

UNIX Data AnalysisLoadable Kernel Modules

LKM can by dynamically loaded with root-level access.

Used to let a hacker maintain access.

Adore, Knark, Itf

UNIX Data AnalysisLoadable Kernel Modules

Trojan system utilities used to detect them.

Look for discrepancies between internal and external scans.

Detection tools are available.