Physical Memory Forensics
Mariusz Burdach
Overview
• Introduction
• Anti-forensics
• Acquisition methods
• Memory analysis of Windows & Linux
– Recovering memory mapped files – Detecting hidden data – Verifying integrity of core memory components
• Tools
• Q & A
Analysis Types
Application Analysis
Swap Space Analysis
File System
Database Analysis
Analysis
Volume Analysis Memory Analysis
Physical Storage Media Analysis Network Analysis
Source: „File System Forensic Analysis”, Brian Carrier
RAM Forensics
• Memory resident data
• Correlation with Swap Areas
• Anti-Forensics against the data:
– Data contraception – Data hiding – Data destruction
• Anti-Forensic methods:
– Data contraception against File System Analysis – Data hiding against Memory Analysis
In-memory data
• Current running processes and terminated processes
• Open TCP/UDP ports/raw sockets/active connections
• Memory mapped files
– Executable, shared, objects (modules/drivers), text files
• Caches
– Web addresses, typed commands, passwords, clipboards,
SAM database, edited files
• Hidden data and many more
• DEMO
Persistence of Data in Memory
• Factors:
• System activity
• Main memory size
• Data type
• Operating system
Above example*: Long-term verification of DNS server: (OS: Solaris 8, RAM: 768 MB) Method: Tracking page state changing over time. Result: 86 % of the memory never changes.
*Source: „Forensic Discovery”, Dan Farmer, Wietse Venema
Anti-forensics
• Syscall proxying - it transparently „proxies” a process’ system calls to a remote server:
– CORE Impact
• MOSDEF - a retargetable C compiler, x86 assembler & remote code linker
– Immunity CANVAS
• In-Memory Library Injection – a library is loaded into memory without any disk activity:
– Metasploit’s Meterpreter (e.g. SAM Juicer) – DEMO
Anti-forensics
• Anti-forensic projects focused on data contraception:
– „Remote Execution of binary without creating a file on disk”
by grugq (Phrack #62) – „Advanced Antiforensics : SELF” by Pluf & Ripe (Phrack
#63) – DEMO
• In memory worms/rootkits
– Their codes exist only in a volatile memory and
they are installed covertly via an exploit – Example: Witty worm (no file payload)
Anti-forensics
• Hiding data in memory:
– Advanced rootkits
• Evidence gathering or incident response tools can be cheated
• Examples:
– Hacker Defender/Antidetection – suspended – FUTo/Shadow Walker – Offline analysis will defeat almost all
methods
Anti-forensics
• DKOM (Direct Kernel Object Manipulation)
– Doubly Linked List can be abused – The FU rootkit by Jamie Butler
– Examples: Rootkit technologies in the wild*
Worms that uses DKOM & Physical Memory:
• W32.Myfip.H@mm
• W32.Fanbot.A@mm
e
EPROCESS
BLINK
BEFORE AFTER
P
r
o
c
e
s
s
t
o
h
id
EPROCESS
EPROCESS
EPROCESS
EPROCESS
FLINK
FLINK
FLINK
FLINK
FLINK
BLINK
BLINK
BLINK
BLINK
*Source: „Virus Bulletin” December, 2005, Symantec Security Response, Elia Florio
EPROCESS
FLINK
BLINK
Identifying anti-forensic tools in memory image
• AF tools are not designed to be hidden against Memory Analysis
– Meterpreter
• Libraries are not shared
• Server: metsrv.dll
• Libraries with random name ext??????.dll – SELF
• Executed in memory as an additional process – memory mapped files can be recovered even after process termination
Acquisition methods
• All data in a main memory is volatile – it refers to data on a live system. A volatile memory loses its contents when a system is shut down or rebooted
• It is impossible to verify an integrity of data
• Acquisition is usually performed in a timely manner (Order of Volatility - RFC 3227)
• Physical backup instead of logical backup
• Volatile memory acquisition procedures can be:
– Hardware-based – Software-based
Hardware-based methods
• Hardware-based memory acquisitions
– We can access memory without relying on the
operating system, suspending the CPU and using DMA (Direct Memory Access) to copy contents of physical memory (e.g. TRIBBLE – PoC Device)
• Related work (Copilot Kernel Integrity Monitor, EBSA- 285) – The FIREWIRE/IEEE 1394 specification allows clients’ devices for a direct access to a host memory, bypassing the operating system (128 MB = 15 seconds)
• Example: Several demos are available at http://blogs.23.nu/RedTeam/stories/5201/ by RedTeam
Software-based method
• Software-based memory acquisitions:
– A trusted toolkit has to be used to collect volatile
data
• DD for Windows - Forensic Acquisition Utilities & KNTDD are available at http://users.erols.com/gmgarner/
• DD for Linux by default included in each distribution (part of GNU File Utilities) – Every action performed on a system, whether
initiated by a person or by the OS itself, will alter the content of memory:
• The tool will cause known data to be written to the source
• The tool can overwrite evidence – It is highly possible to cheat results collected in
this way
Linux Physical memory device
• /dev/mem – device in many Unix/Linux systems (RAW DATA)
• /proc/kcore – some pseudo-filesystems provides access to a physical memory through /proc
– This format allows us to use the gdb tool to analyse memory image, but we can simplify tasks by using some tools
Windows Physical memory device
• \.PhysicalMemory - device object in Microsoft Windows 2000/2003/XP/VISTA (RAW DATA)
• \.DebugMemory - device object in Microsoft Windows 2003/XP/VISTA (RAW DATA)
• Simple software-based acquisition procedure
➢ dd.exe if=\.PhysicalMemory
of=\<remote_share>memorydump.img
• Any Windows-based debugging tool can analyse a physical memory „image” after conversion to Microsoft crashdump format
– http://computer.forensikblog.de/en/2006/03/dmp_file_struct
ure.html
Problems with Software-based method
➢An attacker can attack the tool
➢Blocking access to pages which are
mapped with different memory types http://ntsecurity.nu/onmymind/2006/2006-06-01.html ➢Problems with access to a physical memory
from user level
➢Windows 2003 SP1+ & Vista ➢Linux
➢SYS_RAWIO capability of Capability Bounding Set ➢It is vital to use kernel driver
Why physical backup is better?
• Limitations of logical backup
– Partial information
• selected data
• only allocated memory – Rootkit technologies – Many memory and swap space modification
• Incident Response (First Response) Systems
– Set of tools
• Forensic Server Project
• Foundstone Remote Forensics System – Direct calls to Windows API
• FirstResponse - Mandiant
• EnCase Enterprise Edition – Cheating IR tools (DEMO)
Preparation
• Useful files (acquired from a file system): – Kernel image files (ntoskrnl.exe, vmlinux-2.x) – Drivers/modules/libraries – Configuration files (i.e. SAM file, boot.ini)
• These files must be trusted
– File Hash Databases can be used to compare hash sums
• Map of Symbols – System.map file – Some symbols are exported
by core operating system files
System identification
• Information about the analysed memory dump
– The size of a page =4096 (0x1000) bytes – The total size of the physical memory
• Physical Address Extension (PAE)
• HIGHMEM = 896 MB – Architecture 32-bit/64-bit/IA-64/SMP
• Memory layout
– Virtual Address Space/Physical Address Space – User/Kernel land
• Windows kernel offset at 0x80000000
• Linux kernel offset at 0xC0000000 – (Windows) The PFN Database at 0x80C00000 – (Linux) The Mem_Map Database at 0xC1000030 – (Windows) The PTE_BASE at 0xC0000000 (on a non-PAE systems) – Page directory – each process has only one PD
• Knowledge about internal structures is required
(Windows) PTE address = PTE_BASE + (page directory index) * PAGE_SIZE
+ (page table index) * PTE size
(Linux) PA = VA – PAGE_OFFSET
Virtual ->Physical (x86)
Physical ->Virtual (x86)
• PFN & mem_map databases
• Entries represent each physical page of memory on the system (not all pages!)
PFN 000263A3 at address 813D8748
flink 000002D4 blink / share count 00000001 pteaddress E42AF03C
reference count 0001 Cached color 0
restore pte F8A10476 containing page 02597C Active P
Shared
Page Table Entries
• Page Table Entry
• There are PAGE_SHIFT (12) bits in 32-bit value that are free for status bits of the page table entry
• PTE must be checked to identify the stage of a page
• PFN * 0x1000 (Page size) = Physical Address
Correlation with Swap Space
• Linux: A mm_struct contains a pointer to the Page Global Directory (the pgd field)
• Windows: A PCB substructure contains a pointer to the Directory Table Base
• Page Table entries contain index numbers to swapped-out pages when the last-significant bit is cleared
➢Linux: (Index number x 0x1000 (swap header)) +
0x1000 = swapped-out page frame ➢Windows: Index number x 0x1000 = swapped-out
page frame
Methods of analysis
• Strings searching and signatures matching
– extracting strings from images (ASCII &
UNICODE) – identifying memory mapped objects by
using signatures (e.g. file headers, .text sections)
• Interpreting internal kernel structures
• Enumerating & correlating all page frames
Strings & signatures searching
• Any tool for searching of ANSI and UNICODE strings in binary images
– Example: Strings from Sysinternals or WinHex
• Any tool for searching of fingerprints in binary images
– Example: Foremost
• Identifying process which includes suspicious content:
– Finding PFN of Page Table which points to page frame which
stores the string – Finding Page Directory which points to PFN of Page Table
• DEMO
LINUX internal structures
Zones and Memory Map array
• Physical memory is partitioned into 3 zones:
– ZONE_DMA = 16 MB – ZONE_NORMAL = 896 MB – 16 MB – ZONE_HIGHMEM > 896 MB
• The mem_map array at 0xC1000030 (VA)
Important kernel structures
• task_struct structure – mm_struct structure – vm_area_struct structure – inode & dentry structures – e.g. info about
files and MAC times – address_space structure
• mem_map array
– Page descriptor structure
Relations between structures
Windows internal structures
Important kernel structures
• EPROCESS (executive process) block
– KPROCESS (kernel process) block – ETHREAD (executive thread) block – ACCESS_TOKEN & SIDs – PEB (process environment) block – VAD (virtual address descriptor) – Handle table – CreationTime - a count of 100-nanosecond intervals since
January 1, 1601 – Data Section Control Area
• Page frames
• PFN (Page Frame Number) Database
– PFN entries
Relations between structures
Enumerating processes
• Linux
– init_task_union (process number 0)
• The address is exported by a kernel image file
• The address is available in the System.map file
• String searches method – init_task_union struct contains list_head structure – All processes (task_structs) are linked by a doubly
linked list
• Windows
– PsInitialSystemProcess (ntoskrnl.exe) = _EPROCESS
(System) – _EPROCESS blocks are linked by a doubly linked list
Linux: Dumping memory mapped files
• Page Tables to verify the stage of pages
• An address_space struct points to all page descriptors
• Page descriptor
– 0x0 –> list_head struct //doubly linked list – 0x8 –> mapping //pointer to an address_space – 0x14 –> count //number of page frames – 0x34 –> virtual //physical page frame
next page descriptor
0x010abfd8: 0xc1074278 0xc29e9528 0xc29e9528 0x00000001
address_space
0x010abfe8: 0xc1059c48 0x00000003 0x010400cc 0xc1095e04 0x010abff8: 0xc10473fc 0x03549124 0x00000099 0xc1279fa4 0x010ac008: 0xc3a7a300 0xc3123000 (virtual - 0xc0000000) = PA
Linux: Dumping memory mapped files
• Signature (strings or hex values) searching
• Reconstructing objects:
– Finding page descriptor which points to page frame which stores the signature (mem_map array) – Page descriptor points to all related page
descriptors (the sequence is critical) – We have all page frames and size of file (inode
structure)
• DEMO
Windows: Dumping memory mapped files
• Page Tables to check the stage of pages
• Data Section Control Area
• Information from the first page (PE header)
– PEB -> ImageBaseAddress
• Required information:
– the Page Directory of the Process (for dumping process
image file) – the Page Directory of the System process (for dumping
drivers/modules)
Integrity verification
Recovered file
Original file
Original file Recovered file
kd> u 0x77e42cd1
kernel32!GetModuleHandleA:
77e42cd1 837c240400 cmp dword ptr [esp+0x4],0x0
77e42cd6 7418 jz kernel32!GetModuleHandleA+0x1f (77e42cf0)
77e42cd8 ff742404 push dword ptr [esp+0x4]
...
IAT in .rdata
Finding hidden objects
• Methods
– Reading internal kernel structures which are not
modified by rootkits
• List of threads instead list of processes
• PspCidTable
• Etc... – Grepping Objects
• Objects like Driver, Device or Process have static signatures
– Data inside object – Data outside object – Correlating data from page frames
• Elegant method of detecting hidden data
Windows: Finding hidden objects (_EPROCESS blocks)
PFN 00025687 at address 813C4CA8
flink 8823A020 blink / share count 00000097 pteaddress C0300C00
reference count 0001 Cached color 0
restore pte 00000080 containing page 025687 Active M
Modified
• Enumerating PFN database
• Verifying following fields:
– Forward link – linked page frames (Forward link also points to the
address of EPROCESS block) – PTE address – virtual address of the PTE that points to this page – Containing page – points to PFN which points to this PFN
• DEMO
Linux: Finding hidden objects (mm_struct structure)
• Each User Mode process has only one memory descriptor
• Next, we enumerate all page descriptors and select only page frames with memory mapped executable files (the VM_EXECUTABLE flag)
• Relations:
– The mapping filed of a page descriptor points to the
address_space struct – The i_mmap field of an address_space structure points to a
vm_area_struct – The vm_mm field of a vm_area_struct points to memory
descriptor
Windows: Finding hidden objects (_MODULE_ENTRY)
• Scanning physical memory in order to find memory signatures
– Identification of module header (MZ header) – Identification of module structures
• Inside object – Driver Object GREPEXEC http://www.uninformed.org/?v=4&a=2
• Outside object
typedef struct _MODULE_ENTRY {
LIST_ENTRY module_list_entry;
DWORD unknown1[4];
DWORD base;
DWORD driver_start;
DWORD unknown2;
UNICODE_STRING driver_Path;
UNICODE_STRING driver_Name;
}
Detecting modifications of memory
• Offline detection of memory modifications
– System call hooking
• Function pointers in tables (SSDT, IAT, SCT, etc) – Detours
• Jump instructions
• Cross-view verification
– .text sections of core kernel components – values stored in internal kernel tables (e.g. SCT)
SSDT
• Verification of core functions by comparing first few bytes
– Self-modifying kernel code
• Ntoskrnl.exe & Hall.dll
• Finding an address of KiServiceTable
– Memory image file: _KTHREAD (TCB)
• *ServiceTable = 80567940 – Symbols exported by the ntoskrnl.exe
(debug section):
• NtAllocateUuids (0x0010176C)
• NtAllocateVirtualMemory (0x00090D9D)
SSDT in the ntoskrnl.exe
Linux: removing data
• The content of page frames is not removed
• Fields of page descriptors are not cleared completely
– a mapping field points to an address_space struct – a list_head field contains pointers to related page descriptors
• Finding „terminated” files
– Enumerating all page frames - 0x01000030 (PA) – A page descriptor points to an address_space – Information from an address_space struct
• an i_mmap field is cleared
• all linked page frames (clean, dirty and locked pages)
• a host field points to an inode structure which, in turn, points to a dirent structure
Windows: removing data
• The content of page frames is not removed
• All fields in PFN, PDEs & PTEs are cleared completely
• Information from related kernel structures are also cleared
• We can recover particular page frames but it is impossible to correlate them without context
Available tools
• Debugging tools (kcore & crashdump)
• Analysis of Windows memory images
– KNTTools by George M. Garner Jr.
• KNTDD & KNTLIST – WMFT - Windows Memory Forensics
Toolkit at http://forensic.seccure.net
• Analysis of Linux memory images – IDETECT at http://forensic.seccure.net
KNTTOOLS
• KNTDD
• MS Windows 2000SP4/XP+/2003+/Vista
• Conversion to MS crash dump format
• KNTLIST
– Information about system configuration
• System Service & Shadow Service Tables
• IDT & GDT Tables
• Drivers & Devices Objects
• Enumerates network information such as interface list, arp list, address object, NIDS blocks and TCB table – Information about processes
• Threads, Access Tokens
• Virtual Address Space, Working Set
• Handle table, Executive Objects, Section Object
• Memory Subsections & Control Area – References are examined to find hidden data
WMFT
• Support for Windows XP & 2003
• Functionality
– Enumerating processes, modules, libraries (doubly linked
list) – Finding hidden data – processes and modules (grepping
objects & correlating pages) – Verifying integrity of functions – Dumping process image file and modules – Detailed info about processes
• Access Token, Handle Table, Control Area & Subsections, etc – Enumerating & finding PFNs
• To do:
– The disassembly functionality – Support for Vista
Conclusion
• Memory analysis as an integral part of Forensic Analysis
• Evidence found in physical memory can be used to reconstruct crimes:
– Temporal (when) – Relational (who, what, where) – Functional (how)
• Sometimes evidence can be resident only in physical memory
• Must be used to defeat anti-forensic techniques
Q & A
Thank you.
Mariusz.Burdach@seccure.net http://forensic.seccure.net
