Reversing

Snowcrash Barbara d'Urso

#include <IRremote.h>

#define POWER         0xE0E040BF
#define UNO           0xE0E0906F
#define TVKEY         0xE0E0D827
#define ZERO          0xE0E08877
#define CHPIU         0xE0E048B7
#define CHMENO        0xE0E008F7
#define SAMSUNG_BITS 32

IRsend irsend;

void setup()
{
pinMode (3, OUTPUT); //output as used in library
}

void loop() {

irsend.sendSAMSUNG(REPEAT, 32); // Some receivers seem to respond a lot faster when a repeat is sent before the actual command.
delay(35); //This delay is needed for optimal response.
irsend.sendSAMSUNG(ZERO, 32); // hex value, 32 bits
delayMicroseconds(50);

}

http://lirc.sourceforge.net/remotes/samsung/BN59-00940A

1 CMOS Hex Schmitt Trigger CD40106BE;
3 fotoresistori;
3 Condensatori 1 uF;
3 diodi 1N914;

1 CMOS Hex Schmitt Trigger CD40106BE
1 fotoresistore
1 Condensatore 1 uF

Schmitt Trigger Oscillator
Spiegazione
Talking Electronics

NFC Reader
NFC Tools

https://arxiv.org/pdf/1705.02081.pdf

Lack of security protection of communication. Most NFC communications do not include encryption mechanisms during its data exchange, it relies on the short range (i.e., less than 4 cm) to guarantee absence of eavesdropping attacks. However, the attacker can still place the device (i.e., NFC tag or NFC reader/writer) between client and NFC provider (i.e., NFC contactless point-of-sale) to trigger a specific attack such as eavesdrop, URL/URI spoofing. This vulnerability can also be exploited to jam the data exchange between two parties by sending out specific packet at the right timing, which can lead to a deny-of-service (DoS) attack toward the NFC- service provider.

URL/URI spoofing. The authors show that spoofing attacks can be performed to trick the user to see the false information as a valid one. In example, the attacker will design an exactly copy of a user’s trusted website with an almost equal URL so the user does not see the difference if she is not cautious. In addition, to uniform resource identifier (URI) and uniform/universal resource locater (URL) spoofing the research shows that phone call and text-message spoofing using the NFC protocol are also applicable. Furthermore, URI and URL spoofing are specially useful in combination with other attacks (i.e., cross-site request forgery).

Lack of authentication mechanism of NFC device. When the NFC reader reads information from another NFC-enabled device, there is not any authentication mechanisms available. Therefore, there is a potential risk of tag replacement and tag hiding (TRTH) attack. In the TRTH scenario, the NFC tags are overwritten by an attacker with malicious information or the physical tag is replace with another tag prepared by the attacker.

Automatic and non-user intervention URL/URI connection. The proposed attack takes advantage of the non-user inter- vention when the device detects another NFC device in its proximity. The malicious NFC provides an URL/URI to attack the user’s device, as the Android system does not request any user intervention, the device will automatically open the provided link by either other smartphone or NFC-tag. This situation opens security and privacy threads for the device’s owner. Once, the device opens the link, it can be attacked by fingerprinting mechanisms or share the user’s location for example (see more details in Section IV. The URI can also open application services such as contacts to automatically add malicious contacts without user permission request.

The attack can be achieved placing NFC-tags that unlocked Android devices will read in several locations: (1) public transport: in areas where the public transport uses NFC reader we can track user’s movement from one station to another, collect the user’s routine information (i.e., when the user goes to work and back home, where does he work); (2) coffee shop, poster at shopping mall : placing NFC-tags under coffee tables or in locations where users tend to leave the device unlocked, we can collect not only device’s information but also the geo-location as we know where the tag is located. For both situations, we can also collect the mentioned social network profiles or leverage more complex attacks in combination with other documented browser vulnerabilities.

The Term Hacker.

the term “hacker” has evolved quite dramatically over the years as the public’s awareness of technology has increased and as a sensationalist mass media continues to color the public’s opinion of hackers. In the beginning, a hacker was someone who worked passionately for the sake of curiosity and exploration. There were hardware hackers who took it upon themselves to remove the covers from computers to optimize their design (early computers were built out of discrete components, so they could be modified in meaningful ways with simple tools), and there were software hackers who labored to make the most compact and elegant code, since computational resources were scarce and slow. There were hackers who explored the ins and outs of the phone system, and those who explored the roofs and tunnels of buildings of university campuses. Quite often, early hackers engaged in all of these activities. Hackers would share their findings or results (hacks) with each other freely, as their rewards were not financial, but came from satisfying their intellectual curiosity and from the enthusiasm of their peers. As a result, hackers tended to form into meritocratic groups where member- ship and advancement were based entirely upon a person’s ability to hack.

As technology evolved and computers became faster and more inte- grated, hackers found that the effort involved in hardware hacking was not worth the benefits. The interesting pieces of computers were quickly becoming buried deep within hermetically sealed ceramic packages, etched into silicon structures that were difficult to see even with a good microscope. A difficult hardware hack that might double the perfor- mance of a computer was made moot within months by Moore’s Law. On the other hand, software hacking was beginning to focus more on applications and less on algorithms or optimization. The compactness or elegance of a program was no longer directly important as memory and processor power became cheap and plentiful. Besides, compiler technol- ogy had also improved to the point where compiled code ran almost as fast as hand assembly. By the late 80’s, the term “hacker” had grown to imply someone who could write volumes of C code in their sleep and create brilliant applications overnight. The old hardware hackers were either converting to software hackers, or retreating to university labs and corporations that could afford to support their expensive hobbies.

The term “hacker” at that time was increasingly associated with people who cracked passwords and programs to gain access to machines and software that was otherwise off limits. Hollywood was partly responsible for this stereotype, with a slew of movies that portrayed teenagers bringing the world to the brink of nuclear annihilation with a few keystrokes, or closet geniuses creating artificially intelligent cyber- monsters in their basement. 4 Unfortunately, the hyberbole of these movie plots was lost on the general public, and this dark impression of hackers eventually became a dominant part of the hacker stereotype. The inaccuracy of this stereotype contributed to the creation of a term for hackers that focuses primarily upon cracking systems and programs “crackers.”

Linux RE 101

Reverse Engineering - Zoom on Snippet

SECTION .data
my_str:
db 'The pool on the roof must have a leak.', 0
SECTION .text
GLOBAL _start
_start:
nop
push byte 'x' ; second function parameter
push dword my_str ; first function parameter
call black_out ; call function
add esp, 8 ; cleaning out the stack
mov ebx,0 ; parameter for exit call (return value)
mov eax,1 ; exit system call
int 080h ; run system call, see page 79 pal

black_out:
push ebp ; function prologue, save stack base pointer
mov ebp, esp ; point base pointer to ESP
; ------------ start code from book ---------

mov edi, [ebp+8]
; mette in edi l'indirizzo del primo parametro della funzione

mov edx, edi
; backup dell'indirizzo

xor eax, eax
; azzera eax

or ecx, 0FFFFFFFFh
; mette a -1 ecx

repne scasb
; scansiona tutta la stringa fino al byte null 0 presente in eax

add ecx, 2
neg ecx ; nega ecx, 38

mov al, [ebp+0Ch]
; copia il carattere presente in ebp+12
mov edi, edx
; rimette in edi l'indirizzo dell'inizio della stringa

rep stosb
; riempie la stringa di x
mov eax, edx
; copia l'indirizzo della stringa in eax che ritorna il valore della funzione

; ------------ end code from book -----------
mov esp, ebp ; restore stack pointer
pop ebp ; restore stack base pointer
ret

Playing a very basic level of a known wargame the other day I was trying to solve the following problem:
Given an executable (ELF, Linux) which accepts a password as an argument and verifies if this is correct, find this string. As most of the problems, it’s quite easy if you have the right tools (and knowledge of course).
Anyway, I thought the solution(s) would make a nice blog entry, so here it is!
In order to play around with it in my own Ubuntu, I wrote a very simple C program, named pass_cli.c

carlos@dell:~/Dropbox/hacking/wargames$ cat pass_cli.c
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int
main(int argc, char **argv)
{
char password[] = “yomama”;
if(argc < 2)
{
printf(“Usage: %s <password>\n”, argv[0]);
exit(1);
}
if(strncmp(argv[1], password, strlen(password)))
{
printf(“FAIL\n”);
exit(1);
} else {
printf(“WIN\n”);
return(0);
}
return(0); // never reached :)
}
I compiled the program with no special options.
carlos@dell:~/Dropbox/hacking/wargames$ file pass_cli
pass_cli: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.15, not stripped
A first tool of the trade when you are looking for strings in a binary is strings, which will look for strings of printable characters inside the binary.
carlos@dell:~/Dropbox/hacking/wargames$ strings pass_cli
/lib/ld-linux.so.2
`:6K*
__gmon_start__
libc.so.6
_IO_stdin_used
exit
strncmp
puts
printf
strlen
__libc_start_main
GLIBC_2.0
PTRh`
yomaf
[^_]
Usage: %s <password>
FAIL
Well, we cannot find the password here (and even if it were displayed here, how could you identify it?) but that gave us some preliminar information about the program. We can see some familiar libc functions (printf, strlen, strncmp, etc.), strncmp will be of interest a bit later.
Another method you could have tried is for example to dump the contents of the .text section inside the binary. This is actually the same idea behind the use of strings, just a lot messier ;)
Remember that the .text section of a binary contains the machine instructions (the compiled code) but that doesn’t mean the strings are neccesarily stored in a readable way. Anyway we could check the contents of this section with the help of objdump.
carlos@dell:~/Dropbox/hacking/wargames$ objdump

-h, –[section-]headers Display the contents of the section headers

-T, –dynamic-syms Display the contents of the dynamic symbol table

carlos@dell:~/Dropbox/hacking/wargames$ objdump -h pass_cli

CONTENTS, ALLOC, LOAD, READONLY, CODE
13 .text 000001fc 08048400 08048400 00000400 2**4 <—- here

This section starts at the address 0x08048400, that is, the offset is 0x400 (the start virtual address is 0x08048000)
Armed with this knowledge we could hexdump this section and manually inspect it
carlos@dell:~/Dropbox/hacking/wargames$ hexdump -C -s 0x400 pass_cli | less

000004c0 19 79 6f 6d 61 66 c7 44 24 1d 6d 61 c6 44 24 1f |.yomaf.D$.ma.D$.| <— :(
As we can see, the string isn’t stored in a readable format, as expected :(
A very useful tool in this case is “ltrace” for we can monitor every system call (with the corresponding arguments!)
carlos@dell:~/Dropbox/hacking/wargames$ ltrace ./pass_cli AAAAA
__libc_start_main(0x80484b4, 2, 0xbf952854, 0x8048570, 0x8048560 <unfinished …>
strlen(“yomama”) = 6
strncmp(“AAAAA”, “yomama”, 6) = -1 <— TA-DA!!!! :)
puts(“FAIL”FAIL
) = 5
exit(1 <unfinished …>
+++ exited (status 1) +++
But what if our system doesn’t have this tool? Then we have to take the heavy weapons and perform some elegant debugging :)
carlos@dell:~/Dropbox/hacking/wargames$ objdump -T pass_cli
pass_cli: file format elf32-i386
DYNAMIC SYMBOL TABLE:
00000000 w D *UND* 00000000 __gmon_start__
00000000 DF *UND* 00000000 GLIBC_2.0 __libc_start_main
00000000 DF *UND* 00000000 GLIBC_2.0 strlen
00000000 DF *UND* 00000000 GLIBC_2.0 printf
00000000 DF *UND* 00000000 GLIBC_2.0 puts
00000000 DF *UND* 00000000 GLIBC_2.0 strncmp <—- idea!
00000000 DF *UND* 00000000 GLIBC_2.0 exit
0804861c g DO .rodata 00000004 Base _IO_stdin_used
We have very good reasons to suspect that strncmp is being used to check our input against the password so let’s start the program in gdb and quickly disassemble it in order to localize the call to strncmp.
carlos@dell:~/Dropbox/hacking/wargames$ gdb -q ./pass_cli
Reading symbols from /home/carlos/Dropbox/hacking/wargames/pass_cli…(no debugging symbols found)…done.
(gdb) set disassembly-flavor intel <—- PLEASE ;)
(gdb) disass main
Dump of assembler code for function main:
0x080484b4 <+0>: push ebp
0x080484b5 <+1>: mov ebp,esp
0x080484b7 <+3>: and esp,0xfffffff0
0x080484ba <+6>: sub esp,0x20
0x080484bd <+9>: mov DWORD PTR [esp+0x19],0x616d6f79
0x080484c5 <+17>: mov WORD PTR [esp+0x1d],0x616d
0x080484cc <+24>: mov BYTE PTR [esp+0x1f],0x0
0x080484d1 <+29>: cmp DWORD PTR [ebp+0x8],0x1
0x080484d5 <+33>: jg 0x80484f9
0x080484d7 <+35>: mov eax,DWORD PTR [ebp+0xc]
0x080484da <+38>: mov edx,DWORD PTR [eax]
0x080484dc <+40>: mov eax,0x8048620
0x080484e1 <+45>: mov DWORD PTR [esp+0x4],edx
0x080484e5 <+49>: mov DWORD PTR [esp],eax
0x080484e8 <+52>: call 0x80483bc
0x080484ed <+57>: mov DWORD PTR [esp],0x1
0x080484f4 <+64>: call 0x80483ec
0x080484f9 <+69>: lea eax,[esp+0x19]
0x080484fd <+73>: mov DWORD PTR [esp],eax
0x08048500 <+76>: call 0x80483ac
0x08048505 <+81>: mov edx,eax
0x08048507 <+83>: mov eax,DWORD PTR [ebp+0xc]
0x0804850a <+86>: add eax,0x4
0x0804850d <+89>: mov eax,DWORD PTR [eax]
0x0804850f <+91>: mov DWORD PTR [esp+0x8],edx
0x08048513 <+95>: lea edx,[esp+0x19]
0x08048517 <+99>: mov DWORD PTR [esp+0x4],edx
0x0804851b <+103>: mov DWORD PTR [esp],eax
0x0804851e <+106>: call 0x80483dc
0x08048523 <+111>: test eax,eax
0x08048525 <+113>: je 0x804853f
0x08048527 <+115>: mov DWORD PTR [esp],0x8048636
[…]
Now I will place a breakpoint exactly on the address of this call instruction.
(gdb) b *0x0804851e
Breakpoint 1 at 0x804851e
Remember to use the asterisk (*) right in front of the address, so gdb understands what follows isn’t a literal.
Why did I do it this way? Think about it the other way. What happens when the call instruction is executed? The whole stack frame stup parafernalia, namely
EIP is pushed to the stack (by the call itself)
The function prologue is executed, that is
the current value of EBP is pushed to the stack (from now on, known as SFP)
the current value of ESP passes to be the new EBP (“a new stack frame starts here”)
a value is subtracted from ESP (to allocate space for local variables)
That is too messy to keep track of, so if we stop the execution flow right before the call instruction, what we have is the stack right before all this stuff… the function arguments at the top of the stack ;)
(gdb) run AAAAAA
Starting program: /home/carlos/Dropbox/hacking/wargames/pass_cli AAAAAA
Breakpoint 1, 0x0804851e in main () <— breakpoint is hit
(gdb) info reg
eax 0xbffff620 -1073744352
ecx 0x6 6
edx 0xbffff3c9 -1073744951
ebx 0x283ff4 2637812
esp 0xbffff3b0 0xbffff3b0 <— “top” of the stack
ebp 0xbffff3d8 0xbffff3d8
esi 0x0 0
edi 0x0 0
eip 0x804851e 0x804851e
eflags 0x286 [ PF SF IF ]
cs 0x73 115
ss 0x7b 123
ds 0x7b 123
es 0x7b 123
fs 0x0 0
gs 0x33 51
Let’s examine the top of the stack. We are actually interested in the first three words.
(gdb) x/12x $esp
0xbffff3b0: 0xbffff620 0xbffff3c9 0x00000006 0xbffff3d8
0xbffff3c0: 0x0015d4a5 0x0011e0c0 0x6d6f797b 0x00616d61
0xbffff3d0: 0x08048570 0x00000000 0xbffff458 0x00144bd6
Without further inspection we can see a 6, the number of char the function has to compare. It looks good at least ;) Let’s remember the exact syntaxis of strncmp()
carlos@dell:~/Dropbox/hacking/wargames$ man 3 strncmp
[…]
SYNOPSIS
#include
int strcmp(const char *s1, const char *s2);
int strncmp(const char *s1, const char *s2, size_t n); <— allright, three arguments…
[…]
Also one of the first two words must be a pointer to the hardcoded password, the other a pointer to the user input (argv[1] in this case)
(gdb) x/4x 0xbffff620
0xbffff620: 0x41414141 0x4f004141 0x54494252 0x434f535f
Well, this is pretty clearly our string of 6 “A’s” null-terminated. The other address must be the location of our password!
(gdb) x/4x 0xbffff3c9
0xbffff3c9: 0x616d6f79 0x7000616d 0x00080485 0x58000000
OK, another string of 6 characters, null-terminated. The ASCII char associated to these values can be displayed in gdb as follows:
(gdb) p/c *0xbffff3c9
$16 = 121 ‘y‘
(gdb) p/c *0xbffff3ca
$17 = 111 ‘o‘
(gdb) p/c *0xbffff3cb
$18 = 109 ‘m‘
(gdb) p/c *0xbffff3cc
$19 = 97 ‘a‘
(gdb) p/c *0xbffff3cd
$20 = 109 ‘m‘
(gdb) p/c *0xbffff3ce
$21 = 97 ‘a‘
(gdb) p/c *0xbffff3cf
$22 = 0 ‘00‘

So here’s the magic password! YOMAMA! ;)

1 OPAMP UA741
2 Resistor 1MΩ
1 Resistor 2k2
1 NPN Transistor 2N2222A
1 47n Capacitor

------------------------------

C1 Ceramic Capacitor capacitance 10nF;
J1 Piezo Speaker;
R1 Rotary Potentiometer resistance 10kΩ;
R2 Resistor resistance 100Ω;
R3 Resistor resistance 470Ω;
R4 Resistor resistance 1kΩ;
U1 555 Timer package DIP8
VCC1 Battery & Connector voltage 9V