hacking-the-art-of-exploitation

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114 0x200 Play around with this program a little bit. The Find the Ace game is a demonstration of a principle of conditional probability; although it is counterintuitive, changing your pick will increase your chances of finding the ace from 33 percent to 50 percent. Many people have difficulty understanding this truth—that’s why it’s counterintuitive. The secret of hacking is understanding little-known truths like this and using them to produce seemingly magical results.
0x300 EXPLOITATION Program exploitation is a staple of hacking. As demonstrated in the previous chapter, a program is made up of a complex set of rules following a certain execution flow that ultimately tells the computer what to do. Exploiting a program is simply a clever way of getting the computer to do what you want it to do, even if the currently running program was designed to prevent that action. Since a program can really only do what it’s designed to do, the security holes are actually flaws or oversights in the design of the program or the environment the program is running in. It takes a creative mind to find these holes and to write programs that compensate for them. Sometimes these holes are the products of relatively obvious programmer errors, but there are some less obvious errors that have given birth to more complex exploit techniques that can be applied in many different places.
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CD INside 2nd Edition Hacking the a
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® San Francisco
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BRIEF CONTENTS Preface ............
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0x300 EXPLOITATION 115 0x310 Genera
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0x6a0 Hardening Countermeasures....
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ACKNOWLEDGMENTS I would like to tha
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2 0x100 The rules for this problem
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4 0x100 overly simplistic encryptio
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can be written to accomplish any gi
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0x230 Control Structures Without co
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lest it continue into infinity. A w
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called constants. Returning to the
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Quite often in programs, variables
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0x244 Functions Sometimes there wil
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void turn(variable_direction, targe
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library, a function prototype is ne
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Like a row of houses on a local str
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Below, GDB is used to show the stat
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There are also operations that are
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The display format also uses a sing
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The first four bytes are shown both
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(gdb) x/10i $eip 0x804838b : cmp DW
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022 18 12 DC2 122 82 52 R 023 19 13
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familiar address of EBP minus 4 int
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the English language, knowledge of
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Function "strcpy" not defined. Make
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only be in one of 2 32 possible bit
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pointer.c #include #include int m
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addressof.c #include int main() {
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0x264 Format Strings The printf() f
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The final line just shows the addre
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As discussed earlier, dividing the
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} } printf("[char pointer] points t
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Naturally, it is far easier just to
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This is rather hacky, but since thi
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eader@hacking:~/booksrc $ ./a.out '
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0x267 Variable Scoping Another inte
Page 78 and 79: [in func1] i = 5, j = 42 [in func2]
Page 80 and 81: 10 (gdb) break 7 Breakpoint 1 at 0x
Page 82 and 83: Notice that the static_var retains
Page 84 and 85: 70 0x200 The heap segment is a segm
Page 86 and 87: End of assembler dump (gdb) disass
Page 88 and 89: 0x804836f : mov DWORD PTR [esp+8],0
Page 90 and 91: int global_initialized_var = 5; voi
Page 92 and 93: int main(int argc, char *argv[]) {
Page 94 and 95: errorchecked_heap.c #include #incl
Page 96 and 97: The bar code on the back of this bo
Page 98 and 99: eader@hacking:~/booksrc $ ./simplen
Page 100 and 101: } printf("\n"); display_flags("O_WR
Page 102 and 103: eader@hacking:~/booksrc $ chmod 731
Page 104 and 105: uid_demo.c #include int main() { p
Page 106 and 107: } void fatal(char *); // A function
Page 108 and 109: #define FILENAME "/var/notes" int p
Page 110 and 111: [DEBUG] found a 34 byte note for us
Page 112 and 113: of current_time, an empty tm struct
Page 114 and 115: While struct memory can be accessed
Page 116 and 117: 815015288 1315541117 2080969327 450
Page 118 and 119: printf("6 - Reset your account at 1
Page 120 and 121: int fd; } printf("\n===============
Page 122 and 123: } } // This function is the Pick a
Page 124 and 125: invalid_choice = 1; while(invalid_c
Page 126 and 127: Would you like to play again? (y/n)
Page 130 and 131: A program can only do what it’s p
Page 132 and 133: don’t say exactly what their crea
Page 134 and 135: By now, you should be able to read
Page 136 and 137: eader@hacking:~/booksrc $ gcc explo
Page 138 and 139: 11 if(strcmp(password_buffer, "bril
Page 140 and 141: auth_overflow2.c #include #include
Page 142 and 143: As expected, the overflow cannot di
Page 144 and 145: (gdb) c Continuing. Breakpoint 2, c
Page 146 and 147: Notice the two lines shown in bold
Page 148 and 149: eader@hacking:~/booksrc $ perl -e '
Page 150 and 151: 0x0804848d : mov eax,DWORD PTR [eax
Page 152 and 153: 20 offset = atoi(argv[1]); (gdb) 21
Page 154 and 155: called the NOP sled, that can assis
Page 156 and 157: The function of the for loop should
Page 158 and 159: \x2f\x2f\x73\x68\x68\x2f\x62\x69\x6
Page 160 and 161: eader@hacking:~/booksrc $ ./notesea
Page 162 and 163: int main(int argc, char *argv[]) {
Page 164 and 165: char *buffer = (char *) malloc(160)
Page 166 and 167: 7e99000-b7e9a000 rw-p b7e99000 00:0
Page 168 and 169: for that user. Using the salt value
Page 170 and 171: 0x342 Overflowing Function Pointers
Page 172 and 173: 7 - Quit [Name: Jon Erickson] [You
Page 174 and 175: 0804b630 A _edata 0804b6d4 A _end 0
Page 176 and 177: n 5 AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
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6 - Reset your account at 100 credi
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[Name: Jon Erickson] [You have 1230
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Parameter Input Type Output Type %d
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This is an interesting detail that
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0x353 Reading from Arbitrary Memory
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The wrong way to print user-control
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The addresses and junk data at the
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eader@hacking:~/booksrc $ reader@ha
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0x355 Direct Parameter Access Direc
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Since the stack doesn’t need to b
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0x357 Detours with .dtors In binary
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located. Then the actual bytes are
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Since the .dtors section is writabl
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[DEBUG] found a 34 byte note for us
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eader@hacking:~/booksrc $ objdump -
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0x400 NETWORKING Communication and
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For example, whenever you browse th
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Datagram sockets and UDP are common
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From /usr/include/bits/socket.h /*
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htons(short value) Host-to-Network
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fatal("in socket"); if (setsockopt(
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When compiled and run, the program
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This reveals that the webserver is
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From /usr/include/netdb.h /* Descri
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} while(recv_line(sockfd, buffer))
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} /* This function handles the conn
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Accepting web requests on port 80 G
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the two addressing schemes. In the
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also exist on this layer. ICMP pack
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0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3
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Interrupt:16 Base address:0x2024 re
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u_char buffer[9000]; if ((sockfd =
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pcap_handle = pcap_open_live(device
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eader@hacking:~/booksrc $ $ grep -R
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The compiler padding, as mentioned
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Now that the headers are defined as
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The caught_packet() function gets c
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With the headers decoded and separa
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Due to timeout values, the victim m
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eader@hacking:~/booksrc $ sudo neme
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data structures for the packet head
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if (pd->file_mem == NULL) pd->file_
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only builds ethernet/IP ARP packets
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The remaining libnet functions get
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dest_ip = libnet_name_resolve(argv[
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In the example above, the host 192.
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0x454 Ping Flooding Flooding DoS at
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The host machine will receive the s
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char errbuf[PCAP_ERRBUF_SIZE]; // S
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TH_RST, // Control flags (RST flag
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Christmas tree), and the Null scan
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0x475 Proactive Defense (shroud) Po
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char errbuf[PCAP_ERRBUF_SIZE]; // S
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NULL, // Payload (none) 0, // Paylo
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} while(recv(sockfd, ptr, 1, 0) ==
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$1 = 540 (gdb) p /x 0xbffff5c0 + 20
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" 90 90 90 90 90 90 90 90 90 90 90
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When this exploit is compiled and r
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0x500 SHELLCODE So far, the shellco
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mmap2(0xb7ee4000, 9596, PROT_READ|P
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#define __NR_stime 25 #define __NR_
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In shellcode, the bytes for the str
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eader@hacking:~/booksrc $ export SH
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which means that a small value like
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Instruction inc dec Description I
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After assembling this shellcode, he
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exec_shell.s BITS 32 jmp short two
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eader@hacking:~/booksrc $ nasm tiny
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int setresuid(uid_t ruid, uid_t eui
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push BYTE 11 pop eax push ecx push
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So, to make socket system calls usi
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push BYTE 16 ; argv: { sizeof(serve
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00000030 80 b0 66 43 52 52 56 89 e1
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This loop iterates ECX from 0 to 2,
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push edx ; Build sockaddr struct: I
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pop eax inc ebx ; ebx = 2 (needed f
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the return address uses multiple by
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0x600 COUNTERMEASURES The golden po
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0x620 System Daemons To have a real
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} printf("Caught signal %d\t", sign
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tinywebd.c #include #include #inc
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if(fd == -1) { // If file is not fo
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In previous chapters, we’ve writt
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63 if (listen(sockfd, 20) == -1) 64
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message. Shell variables are used f
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There’s a simple mistake in the t
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any program to show every system ca
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0x080487ee : mov DWORD PTR [esp+8],
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0x08048f5f : call 0x08048f64 : nop
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push BYTE 0x6 ; Close () pop eax in
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A quick glance at the function prol
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push edx ; Build arg array: { proto
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This program can be used to inject
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Then, from another terminal, the ne
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strace is used with the -p command-
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ig red flag. We could change the po
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of new_sockfd will still be correct
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00000020 b0 3f cd 80 49 79 f9 b0 0b
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push ebx mov ecx, esp int 0x80 ; pu
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Instruction Hex ASCII inc eax 0x40
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eader@hacking:~/booksrc $ gcc -o up
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Amazingly, these instructions, comb
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ESP up (toward lower memory address
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eader@hacking:~/booksrc $ gcc -o pr
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At the end, the shellcode has been
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esp 0xbffffa2c 0xbffffa2c eax 0x0 0
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functions are shared, so any progra
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A quick binary search shows that th
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eginning of the buffer. When a prog
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The breakpoint is set at the last i
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Bouncing off linux-gate refers to a
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matrix@loki /hacking $ for i in `se
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manual page for execve() for detail
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for(i=0; i < 90; i+=4) // Fill buff
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encryption, credit card transaction
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through the incorrect filter, its p
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This means that, in general, the gr
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Without some way to manipulate the
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With a little bit of basic algebra,
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Since this is all done modulo N, th
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0x750 Hybrid Ciphers A hybrid crypt
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[:] - Static route to port on host
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communication channel with the atta
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e asked to add the new fingerprint.
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to be a bit hazy. The goal behind t
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---[Current State]-----------------
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0x760 Password Cracking Passwords a
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crypt_crack.c #define _XOPEN_SOURCE
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Custom dictionary files are often m
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possible hashes for a single plaint
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Of course, there are downsides. Fir
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charval = (k-32)*95 + (l-32); // La
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} /* Print the plaintext pairs that
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printf("Building probability vector
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Of course, if WEP is turned on, onl
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Now when keystream data is needed,
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After an IV collision is discovered
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is really quite amazing. It takes a
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Seed = IV concatenated with the key
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int key[13] = {1, 2, 3, 4, 5, 66, 7
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and the key is hard-coded into the
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9 0 | 41 1 | 73 0 | 105 0 | 137 1 |
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0x800 CONCLUSION Hacking tends to b
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CNET News. “40-Bit Crypto Proves
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INDEX Symbols & Numbers & (ampersan
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uffer overrun, 119 buffers, 38 prog
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dtors_sample.c program, 184 dump()
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declaring as void, 17 for error che
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Internet Protocol (IP), 220 address
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nemesis_arp() function, 245 nemesis
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pointer_types4.c program, 56 pointe
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session layer (OSI), 196 for web br
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text segment, of memory, 69 then ke
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More No-Nonsense Books from NO STAR
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UPDATES Visit http://www.nostarch.c
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