hacking-the-art-of-exploitation

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The two major protocols at this layer are the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). TCP is the most commonly used protocol for services on the Internet: telnet, HTTP (web traffic), SMTP (email traffic), and FTP (file transfers) all use TCP. One of the reasons for TCP’s popularity is that it provides a transparent, yet reliable and bidirectional, connection between two IP addresses. Stream sockets use TCP/IP connections. A bidirectional connection with TCP is similar to using a telephone—after dialing a number, a connection is made through which both parties can communicate. Reliability simply means that TCP will ensure that all the data will reach its destination in the proper order. If the packets of a connection get jumbled up and arrive out of order, TCP will make sure they’re put back in order before handing the data up to the next layer. If some packets in the middle of a connection are lost, the destination will hold on to the packets it has while the source retransmits the missing packets. All of this functionality is made possible by a set of flags, called TCP flags, and by tracking values called sequence numbers. The TCP flags are as follows: TCP flag Meaning Purpose URG Urgent Identifies important data ACK Acknowledgment Acknowledges a packet; it is turned on for the majority of the connection PSH Push Tells the receiver to push the data through instead of buffering it RST Reset Resets a connection SYN Synchronize Synchronizes sequence numbers at the beginning of a connection FIN Finish Gracefully closes a connection when both sides say goodbye These flags are stored in the TCP header along with the source and destination ports. The TCP header is specified in RFC 793. From RFC 793 [Page 14] September 1981 Transmission Control Protocol 3. FUNCTIONAL SPECIFICATION 3.1. Header Format TCP segments are sent as internet datagrams. The Internet Protocol header carries several information fields, including the source and destination host addresses [2]. A TCP header follows the internet header, supplying information specific to the TCP protocol. This division allows for the existence of host level protocols other than TCP. TCP Header Format 222 0x400
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Acknowledgment Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Data | |U|A|P|R|S|F| | | Offset| Reserved |R|C|S|S|Y|I| Window | | | |G|K|H|T|N|N| | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Checksum | Urgent Pointer | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Options | Padding | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ TCP Header Format Note that one tick mark represents one bit position. Figure 3. The sequence number and acknowledgment number are used to maintain state. The SYN and ACK flags are used together to open connections in a three-step handshaking process. When a client wants to open a connection with a server, a packet with the SYN flag on, but the ACK flag off, is sent to the server. The server then responds with a packet that has both the SYN and ACK flags turned on. To complete the connection, the client sends back a packet with the SYN flag off but the ACK flag on. After that, every packet in the connection will have the ACK flag turned on and the SYN flag turned off. Only the first two packets of the connection have the SYN flag on, since those packets are used to synchronize sequence numbers. SYN packet SYN on ACK off seq # = 324808530 ack # = 0 Client SYN/ACK packet SYN on ACK on seq # = 288666267 ack # = 324808531 Server ACK packet SYN off ACK on seq # = 324808531 ack # = 288666268 Networking 223
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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
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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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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 -
Page 209 and 210: 0x400 NETWORKING Communication and
Page 211 and 212: For example, whenever you browse th
Page 213 and 214: Datagram sockets and UDP are common
Page 215 and 216: From /usr/include/bits/socket.h /*
Page 217 and 218: htons(short value) Host-to-Network
Page 219 and 220: fatal("in socket"); if (setsockopt(
Page 221 and 222: When compiled and run, the program
Page 223 and 224: This reveals that the webserver is
Page 225 and 226: From /usr/include/netdb.h /* Descri
Page 227 and 228: } while(recv_line(sockfd, buffer))
Page 229 and 230: } /* This function handles the conn
Page 231 and 232: Accepting web requests on port 80 G
Page 233 and 234: the two addressing schemes. In the
Page 235: also exist on this layer. ICMP pack
Page 239 and 240: 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
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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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