Linux forensics


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Linux forensics

  1. 1. Linux Forensics SANTOSH KHADSARE
  2. 2. WindowsAdvantages:• Easy to understand.• GUI interface.Disadvantages:• Less Secure.• More vulnerable.
  3. 3. LinuxAdvantages:• High security.• More tools and automation.Disadvantages:• Hard to understand interface.• Difficult to administrate.
  4. 4. Windows versus Linux Server Type Windows LinuxWeb Server IIS ApacheDatabase Server Spl Mysql,PostgresqlDNS Server Own BindFTP Server Own PROFTPDEmail Server MS exchange Sendmail, Qmail
  5. 5. Before Linux• In 80’s, Microsoft’s DOS was the dominated OS for PC• Apple MAC was better, but expensive• UNIX was much better, but much, much more expensive. Only for minicomputer for commercial applications• People was looking for a UNIX based system, which is cheaper and can run on PC• Both DOS, MAC and UNIX were proprietary, i.e., the source code of their kernel is protected• No modification is possible without paying high license fees
  6. 6. GNU project– Established in 1984 by Richard Stallman, who believes that software should be free from restrictions against copying or modification in order to make better and efficient computer programs GNU is a recursive acronym for “GNUs Not Unix” Aim at developing a complete Unix-like operating system which is free for copying and modification Companies make their money by maintaining and distributing the software, e.g. optimally packaging the software with different tools (Redhat, Slackware, Mandrake, SuSE, etc) Stallman built the first free GNU C Compiler in 1991. But still, an OS was yet to be developed
  7. 7. Beginning of Linux– A famous professor Andrew Tanenbaum developed Minix, a simplified version of UNIX that runs on PC– Minix is for class teaching only. No intention for commercial use– In Sept 1991, Linus Torvalds, a second year student of Computer Science at the University of Helsinki, developed the preliminary kernel of Linux, known as Linux version 0.0.1
  8. 8. Beginning of Linux
  9. 9. What is good about using Linux for forensics?– Most tools are free of charge .– Most tools are open source (Allows you to know exactly what the tool is doing).– Environment is very flexible.– When tools are used properly, evidence should stand up in court.
  10. 10. limitations of using Linux for forensics?– Most tools are free - you don’t get any tech support and may not be able to call the author in to court if necessary .– Most tools are open source, which allows those who oppose you in court to scour the code for bugs and try to call the tool into question.– Environment is very flexible - it is often difficult to decide what is the best way to do something and there are no universally accepted standard procedures.
  11. 11. limitations of using Linux for forensics?– Free tools are not as full featured as commercial packages.– Tools are significantly more complicated to use than commercial packages and most involve using the command line.– In many operations, especially when imaging, you can destroy your work or even your original evidence with a typo.
  12. 12. Linux is Growing in Popularity• Each new version becoming more user friendly. – Disk installation no longer confusing. – Installation interface more intuitive. – Graphical environment becoming much more mature.• More and more companies are embracing & supporting Linux. – IBM has teams of developers working on it. – Apple’s OS now has a UNIX-like core. – Novell is now in the Linux business.• More and more devices are now running Linux – Personal Devices: Cell Phones & PDA’s. – Electronics: Video Recorders, MP3 Players.
  13. 13. Why Linux• Linux is a powerful operating system. – Many web sites use Linux as the operating system. – Even Steve Ballmer of Microsoft said Linux has 60% of the server market in 2008. – Tolerant of a range of hardware platforms without special configuration.• Computer Forensics need to be able to consider server forensics. – Forensic issues can happen on server platforms too.• Host-Based forensic tools often run on linux platforms. – Free platform – Flexible and reliable – Easier to access low-level interfaces – Good forensic qualities. – Will consider Caine (a Linux live cd) for host-based forensics, which runs The Forensic Toolkit and Autopsy.
  14. 14. Linux Shell whoami ls pwd Shell interprets the command and Bash, Tcsh, Zsh request service from kernel Similar to DOS but DOS has only one set of interface while Linux can select Kernel different shell – Bourne Again shell (Bash), TC shell (Tcsh), Z shell (Zsh) Different shell has similar but different functionality Bash is the default for Linux Graphical user interface of Linux is in fact an application program work on the shell
  15. 15. GRUB• GNU GRUB (short for GNU GRand Unified Bootloader) is a boot loader package from the GNU Project.• GRUB is the reference implementation of the Multiboot Specification, which provides a user the choice to boot one of multiple operating systems installed on a computer or select a specific kernel configuration available on a particular operating systems partitions.
  16. 16. KERNEL
  17. 17. KERNEL• Typically, a kernel (or any comparable center of an operating system) includes an interrupt handler that handles all requests or completed I/O operations that compete for the kernels services, a scheduler that determines which programs share the kernels processing time in what order, and a supervisor that actually gives use of the computer to each process when it is scheduled.• A kernel may also include a manager of the operating systems address spaces in memory or storage, sharing these among all components and other users of the kernels services. A kernels services are requested by other parts of the operating system or by application programs through a specified set of program interfaces sometimes known as system calls.
  18. 18. KERNEL
  19. 19. KERNEL VERSION• UBUNTU 11.0 running• What is kernel version?
  20. 20. KERNEL VERSION• UBUNTU 11.0 –say company name• TYPE umane –r to find the kernel .• UBUNTU 11.0 has 2.6.38 kernel version.• We can also kind kernel when we start a linux machine. (GRUB)
  21. 21. Kernel
  22. 22. KDE and GNOME
  23. 23. KDE and GNOME• KDE and GNOME are two desktop environments (collection of software that provides certain functionality and a look and feel for operating systems) that run on operating systems that use X Window System (mostly Unix, Linux, Solaris, FreeBSD, and Mac OS X).• KDE’s main programming language is C++. The main reason for this is that the main functionality of KDE is coded using QT, which is written in C+ +. It takes approximately 210MBs to install the base system of KDE.
  24. 24. KDE and GNOME• GNOME’s main programming language is C, because the tool kit used to write GNOME is GTK+ and it is written in C. Approximately 180 MB is required to install the base system of GNOME . After the recent rebranding,“KDE” actually refers to the whole collection of applications including the desktop environment while GNOME refers to a desktop environment alone.
  25. 25. File management
  26. 26. Directory Tree
  27. 27. Directory Tree (root)When you log on the the Linux OSusing your username you areautomatically located in yourhome directory.
  28. 28. • /bin System binaries, including the command shell• /boot Boot-up routines• /dev Device files for all your peripherals• /etc System configuration files• /home User directories• /lib Shared libraries and modules• /lost+found Lost-cluster files, recovered from a disk-check• /mnt Mounted file-systems• /opt Optional software•/proc Kernel-processes pseudo file-system• /root Administrator’s home directory• /sbin System administration binaries•/usr User-oriented software• /var Various other files: mail, spooling and logging
  29. 29. Directories• /bin : This contains commands a user can run, like ‘ls’, but which might be needed during boot.• /dev : This contains devices, like the mouse.• /home : This is where users store their files.• /tmp : Temporary storage for users and the system• /var : System files which can change.• /etc : System config files which don’t change• /lib : Where all the system libraries live• /proc : Files which represent the running system (like processes).• /sbin : Commands which only an administrator would want.• /usr : Commands which are never needed during bootup.
  30. 30. The most important subdirectories inside the root directory are:• /bin : Important Linux commands available to the average user.• /boot : The files necessary for the system to boot. Not all Linux distributions use this one. Fedora does.• /dev : All device drivers. Device drivers are the files that your Linux system uses to talk to your hardware. For example, theres a file in the /dev directory for your particular make and model of monitor, and all of your Linux computers communications with the monitor go through that file.• /etc : System configuration files.• /home : Every user except root gets her own folder in here, named for her login account. So, the user who logs in with linda has the directory /home/linda, where all of her personal files are kept.• /lib : System libraries. Libraries are just bunches of programming code that the programs on your system use to get things done.
  31. 31. The most important subdirectories inside the root directory are:• /mnt : Mount points. When you temporarily load the contents of a CD-ROM or USB drive, you typically use a special name under /mnt. For example, many distributions (including Fedora) come, by default, with the directory /mnt/cdrom, which is where your CD-ROM drives contents are made accessible.• /root : The root users home directory.• /sbin : Essential commands that are only for the system administrator.• /tmp : Temporary files and storage space. Dont put anything in here that you want to keep. Most Linux distributions (including Fedora) are set up to delete any file thats been in this directory longer than three days.• /usr : Programs and data that can be shared across many systems and dont need to be changed.• /var : Data that changes constantly (log files that contain information about whats happening on your system, data on its way to the printer, and so on).
  32. 32. Important Subdirectories inside the root directory are:• /proc : virtual file sys(imp for forensics).• /etc/passwd: contains all user specific info.• /etc/shadow: stores password.
  33. 33. Home directory• You can see what your home directory is called by entering• pwd (print current working directory)
  34. 34. Useful commands: Command Descriptionls List dir and filesdir See directoryIfconfig See IP address configUseradd Add new userReboot Reboot machineSu Switch userWget To download any file for internetTop See process activityPs Display processes
  35. 35. Useful commands: Command DescriptionVmstat Sys activity, hardware and sys infoUptime Tell how long sys is runningFree Memory usagesDf –h See hard disk spaceCp Copy file or folderLostat Average CPU load, disk activitySar Collect and report sys activityPing Test contvNetstat Network statistics
  36. 36. Useful commands: Command DescriptionIptraf Eal time network statisticsTcpdump Detailed network traffic analysisCat Displays contents of the filevim Opens text editorMount Mounts dirCd Change dirMkdir Make dirRmdir Remove dirPwdshow Show present working dir
  37. 37. The PROMPT• Once you log into your machine, you are at the prompt. Here you can perform your commands.• Everything on linux is either a file or a directory.• A file which is executed becomes a process.• Processes can be seen as files too.• Devices, such as scanners and hard drives are also files.
  38. 38. File System●Windows uses letters of the alphabet to represent different devices and different hard disk partitions. Under Windows, you need to know what volume (C:, D:,...) a file resides on to select it, the files physical location is part of its name.●In Linux all directories are attached to the root directory, which is identified by a forward- slash, "/". - root.● For example, below are some second-level directories:
  39. 39. File System●# - shell command.●# fdisk -l /*list partitions*/●/dev/sda1  /dev – device  /sda1 or /hda1 • sd – SATA /*SATA- tech to read/write data*/ • hd – IDE • a
  40. 40. File System Sd ..a/b/c/d.....1/2/3..... • a – primary master • b – primary slave • c – secondary master • d – secondary slave • 1/2/3... – first/second/third partition
  41. 41. File System●# fdisk /dev/sda /*’m’ for help*/●(if type ‘l’ it will list all available file sys with their Id e.g. Windows -7 and Linux -83)●(‘q’ to quit)●/dev/sda1 - sys reserve●/dev/sda2 - is C:●(windows makes 2 partitions: 100 Mb(from 100 GB) for sys reserve and remaining C: (100GB))
  42. 42. File System
  43. 43. Redirection• If you end a command with “>”, its output goes to a file.• If you end a command with “<“, its input comes from a file.
  44. 44. Linux Help●man●info●command –help●Forums.
  45. 45. Man -k• You can keyword search for commands• For instance, what commands show a calendar?$ man -k calendarcal (1) - displays a calendarcal (1p) - print a calendardifftime (3p) - compute the difference…
  46. 46. man command – The “-k” option ● man –k print – Manual pages are divided in 8 sections:  User commands  System calls  Libc calls  Devices  File formats and protocols  Games  Conventions, macro packages and so forth  System administation – To select correct section, add section number: ● man 1 passwd, man 5 passwd
  47. 47. info command●A program for reading documentation, sometimes a replacement for manual pages●Example : info ls
  48. 48. Linux Boot Sequence• Start your computer that has Linux installed. B IO S P o s t L in u x B o o t L o a d e r L i n u x K e r n e l I n it I n it P ro g r a m B a s h S h e ll S ta r t e d
  49. 49. RUN LEVELS• They initiate sys call which interact with kernel.• Run level 0 : shutdown.• Run level 1 : single user interface.• Run level 2 : multi user without NFS(new file sys) support.• Run level 3 : multi user with NFS(new file sys) support.• Run level 4 GUI.• Run level 5 restart.
  50. 50. Boot sequence summary•BIOS•Master Boot Record (MBR)•LILO or GRUB•Kernel•init•Run Levels
  51. 51. The Linux Environment What exactly is Linux?• "Linux" is just an OS kernel• the rest is additional Open Source Software• together they are a "Linux Distribution"• [Knoppix, Ubuntu, Redhat, Novell/SuSe]Large choice of GUI and/or commandlineenvironments• most popular are KDE and Gnome• Unix-like, Mac-like, MSWindows-like, NeXT-like• advanced shell environments• web front-ends, GUI front-ends• [KDE, Gnome, Windowmaker, bash, zsh, emacs, mc]
  52. 52. The Linux EnvironmentForensic boot CDs• fully installed Linux environment on bootable CD orDVD• non-mount booting• large pre-installed forensic toolset• Knoppix basedMost up to date (at the moment)• FCCU GNU/Linux Forensic Boot CD (Belgian FederalComputer Crime Unit)• Helix (US e-fense Inc.)Full installation:• learning Linux -> Ubuntu, doing forensics -> Debian• must strip down automount services
  53. 53. Imaging and Evidence AcquisitionWide range of supported technologies and media• ATA, SATA, SCSI, USB, Firewire• cd, dvd, USB sticks, tapes, floppies, etcForensically sound acquisition• typically any sector-based storage medium accessibleas adevice can be safely imaged• can acquire an image without mounting drive• hardware write-blocker not needed for unmounteddevices• support for handling errors, bad blocks• [dd, dcfldd, dd_rescue, sdd, AIR, sleuthkit, adepto, grab]
  54. 54. Imaging and Evidence AcquisitionWide range of supported technologies and media• ATA, SATA, SCSI, USB, Firewire• cd, dvd, USB sticks, tapes, floppies, etcForensically sound acquisition• typically any sector-based storage medium accessibleas adevice can be safely imaged• can acquire an image without mounting drive• hardware write-blocker not needed for unmounteddevices• support for handling errors, bad blocks• [dd, dcfldd, dd_rescue, sdd, AIR, sleuthkit, adepto, grab]
  55. 55. Floppy Disk Analysis• Insert Floppy• Obtain SHA hash
  56. 56. Create Floppy Disk Image• Use dd to create forensic image.• Compare SHA hash of image against floppy to confirm good image.
  57. 57. Identify File System• Use file utility to identify the file system of floppy disk image.• file utility can identify more than 30 different file system types & many more standard file types.
  58. 58. Mount the Image for Analysis• Create a directory to mount the image against.• Use mount utility to mount the image, using loop back to trick OS into thinking this is a physical device.
  59. 59. Obtain SHA Hash of Contents• Obtain SHA hash of each file on the floppy disk.• Check file to confirm all looks as expected.
  60. 60. Identify File Contents• ls to view all the files on floppy.• file utility to identify file header. – Tells us that this is actually a Microsoft Office Document.
  61. 61. View File Contents• strings utility to extract raw text from a binary file.
  62. 62. Evidential Search Criteria• Put together keyword list to use in search applied against evidence. – This screenshot shows the use of the vi editor.
  63. 63. Apply Search List• Apply the search list against the entire image of the floppy by using the grep utility.
  64. 64. View Search Results• Viewing the Search Results File with cat shows binary, so we use strings instead to just view the ASCII text from the file. HEX location is shown in [numeric]: I.e. “49189:”
  65. 65. Search Hit Example• xxd utility used to perform a hex dump of data.• # xxd -s 49189 /evidence/floppy1.img | less• Note the match giving an address to the Boston Crackdlr of 11 Clarendon Apt 6 in Boston’s Back Bay
  66. 66. FILE SYSTEM
  67. 67. SECOND EXTENDED FILE SYSTEM(EXT2)• Commonly used in Linux.• Building blocks known as data blocks(4 Kb in size) : similar to FAT32 file sys.• Allocation of blocks similar to FAT32.Thus physical sizes and logical sizes in EXT2 differ as they do in FAT32.• Main components:  Directories.  Inodes.  Data blocks.
  68. 68. SECOND EXTENDED FILE SYSTEM(EXT2)• Directories store the filenames in the file sys and the inodes associated with the files.• In EXT2, files are represented by inodes. An inode contains attributes like file type, size, access rights, timestamps address of data blocks.• An Inode is similar to a directory entry in FAT32. Each inode has a unique no. identifying it.
  69. 69. SECOND EXTENDED FILE SYSTEM(EXT2)• File sys made up of “block groups” a sequential arrangement of a group of data blocks. The entire file sys is thus managed as a series of block groups.• Block group meta data is provided by a ‘block group descriptor’. It contains a copy of super block(size of inode table and file sys), Block bitmap(tracks allocation of each data block), part of inode table and data blocks.
  70. 70. ext2 Characteristics• Complicated internal structure to enhance performance, but on-disk structure is straightforward From: Understanding the Linux Kernel (Bovet/Cesati)
  71. 71. ext2 Directory Structure deleted From: Understanding the Linux Kernel (Bovet/Cesati)
  72. 72. ext2/3: inodeFrom: Understanding the Linux Kernel (Bovet/Cesati)
  73. 73. ext3 Characteristics• Binary compatible with ext2 on-disk• Reason for existence: huge disks == huge amounts of time to restore filesystem consistency after improper shutdown• (Must check inodes, etc.)• Major improvement over ext2: log that stores info about in-progress file operations• On boot, can check log and quickly restore filesystem consistency• Journaling filesystems: DANGER!
  74. 74. File Deletion: Linux• ext2 file deletion – Adjust previous directory entry length to obscure deleted record – No reorganization to make space in directories – “first fit” for new directory entries, based on real name length – Directory entry’s inode # is cleared• ext3 file deletion – Same as for ext2, but… – inode is wiped on file deletion, so block numbers are lost – Major anti-forensics issue! – But directory entry’s inode # isn’t cleared…
  75. 75. Tools• Sleuthkit• Deft 7.0• Helix• BackTrack
  76. 76. Sleuthkit• Linux toolkit for forensics written by Brian Carrier•• Command line tools for forensic analysis under Linux (and now, Windows…)• Graphical interface: Autopsy Forensic Browser
  77. 77. Sleuthkit (2)• Data Unit: – dls – copy individual disk blocks – dcat – copy ranges of disk “chunks” – dstat – determine whether block is allocated• Meta Data: – ils – list inodes (e.g., ones corr. to deleted files!) – icat – copy data associated with inode – istat – dump detailed inode info – ifind – find inode associated with a disk block• File Name: – fls – list files/directories in image – ffind – find filename associated with inode• File System: fsstat – Detailed filesystem information
  78. 78. “Next Generation” Digital Forensics Meets Linux
  79. 79. Filesystem in Userspace (FUSE)• (FUSE) is a loadable kernel module for Unix- like computer operating systems that lets non-privileged users create their own file systems without editing kernel code. This is achieved by running file system code in user space while the FUSE module provides only a "bridge" to the actual kernel interfaces.• FUSE is particularly useful for writing virtual file systems. Unlike traditional file systems that essentially save data to and retrieve data from disk, virtual filesystems do not actually store data themselves. They act as a view or translation of an existing file system or storage device.• In principle, any resource available to a FUSE implementation can be exported as a file system.
  80. 80. FUSE (Filesystem in User Space) Filesystem Implementation dd if=/evidence/DEC/img.dd of=copy.dd FUSE library read()user space C library C librarykernel space FUSE Linux Virtual File System Interface ext3 (VFS) reiserFS
  81. 81. File carving• Is the process of reassembling computer files from fragments in the absence of filesystem metadata.• The carving process makes use of knowledge of common file structures, information contained in files, and heuristics regarding how filesystems fragment data.• Fusing these three sources of information, a file carving system infers which fragments belong together.• File carving is a highly complex task, with a potentially huge number of permutations to try.• To make this task tractable, carving software typically makes extensive use of models and heuristics. This is necessary not only from a standpoint of execution time, but also for the accuracy of the results.
  82. 82. In-Place File Carving client applications scalpel_fs FUSE preview database nbd client local drive network nbd server Scalpel remote driveG. G. Richard III, V. Roussev, V. Marziale, “In-Place File Carving,” submitted to the Third AnnualIFIP WG 11.9 International Conference on Digital Forensics, 2007.
  83. 83. Better AuditingWant: Digital Evidence BagsSee: P. Turner, “Unification of Digital Evidence from Disparate Sources (Digital Evidence Bags),” DFRWS 2005See: Common Digital Evidence Storage Format (CDESF) working group,
  84. 84. Better Auditing (2) dd scalpel TSK FTK … Applications (User space) Block-level Filesystem Data Access Data Access (Kernel) Operating System VFS Interface FDAM Digital Evidence FDAM Block Device Container Import/ DEC Export Evidence Audit Log (DEB, AFF, Data Gfzip …)G. G. Richard III, V. Roussev, "Toward Secure, Audited Processing of Digital Evidence:Filesystem Support for Digital Evidence Bags," Research Advances in Digital Forensics, Springer, 2006.
  85. 85. Bluepipe: On the Spot Digital Forensics Bluepipe PatternsY. Gao, G. G. Richard III, V. Roussev, “Bluepipe: An Architecture for On-the-Spot Digital Forensics,”International Journal of Digital Evidence (IJDE), 3(1), 2004.
  86. 86. <BLUEPIPE NAME=”findcacti”><!-- find illegal cacti pics using MD5 hash dictionary --><DIR TARGET=”/pics/” /><FINDFILEUSEHASHES=TRUELOCALDIR=”cactus”RECURSIVE=TRUERETRIEVE=TRUEMSG="Found cactus %s with hash %h "><FILE ID=3d1e79d11443498df78a1981652be454/><FILE ID=6f5cd6182125fc4b9445aad18f412128/><FILE ID=7de79a1ed753ac2980ee2f8e7afa5005/><FILE ID=ab348734f7347a8a054aa2c774f7aae6/><FILE ID=b57af575deef030baa709f5bf32ac1ed/><FILE ID=7074c76fada0b4b419287ee28d705787/><FILE ID=9de757840cc33d807307e1278f901d3a/><FILE ID=b12fcf4144dc88cdb2927e91617842b0/><FILE ID=e7183e5eec7d186f7b5d0ce38e7eaaad/><FILE ID=808bac4a404911bf2facaa911651e051/><FILE ID=fffbf594bbae2b3dd6af84e1af4be79c/><FILE ID=b9776d04e384a10aef6d1c8258fdf054/></FINDFILE></BLUEPIPE>
  87. 87. Distributed Digital Forensics 750GB 750GBV. Roussev, G. G. Richard III, "Breaking the Performance Wall: The Case for Distributed Digital Forensics,“Proceedings of the 2004 Digital Forensics Research Workshop (DFRWS 2004), Baltimore, MD
  88. 88. Distributed Digital Forensics• Scalable – Want to support at least IMAGE SIZE / RAM_PER_NODE nodes• Platform independent – Want to be able to incorporate any (reasonable) machine that’s available• Lightweight – Horsepower is for forensics, not the framework—less fat• Highly interactive• Extensible – Allow incorporation of existing sequential tools – e.g., stegdetect, image thumbnailing, file classification, hashing, …• Robust – Must handle failed nodes smoothly
  89. 89. Distributed Digital Forensics (2) Worker Coordinator Worker JOIN / LEAVE HASH / GREP / COMMAND/ … CANCEL / EXIT DONE / REPORT / ERROR FETCH CACHE LOADSHUTDOWN STARTUP STORE Local Store Common Store
  90. 90. Distributed Digital Forensics (3) RAID: 504GB File Server CPU: 2x1.4GHz Xeon SCSI RAM: 2GB 1Gb Switch 96-port, 10/100/1000 Mb 24 Gb Backplane Node CPU: 2.4 GHzPentium 4 RAM: 1 GB
  91. 91. Thank you