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CC: Radare2

Date: 02, June, 2021

Author: Dhilip Sanjay S

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Command Line Options

What flag to you set to analyze the binary upon entering the r2 console (equivalent to running aaa once your inside the console)

  • Answer: -A

How do you enable the debugger?

  • Answer: -d

How do you open the file in write mode?

  • Answer: -w

How do you enter the console without opening a file?

  • Answer: -

Analyzation

What command "Analyzes Everything" (all functions and their arguments: Same as running with radare with -A)

  • Answer: aaa

What command does basic analysis on functions?

  • Answer: af

How do you list all functions?

  • Answer: afl

How many functions are in the example1 binary?

  • Answer: 12

  • Steps to Reproduce:

[0x00000530]> afl
0x00000530    1 42           entry0
0x00000560    4 50   -> 44   sym.deregister_tm_clones
0x000005a0    4 66   -> 57   sym.register_tm_clones
0x000005f0    5 50           sym.__do_global_dtors_aux
0x00000520    1 6            sym.imp.__cxa_finalize
0x00000630    4 48   -> 42   entry.init0
0x000004f8    3 23           sym._init
0x000006e0    1 1            sym.__libc_csu_fini
0x000006e4    1 9            sym._fini
0x0000066b    1 7            sym.secret_func
0x00000680    4 93           sym.__libc_csu_init
0x00000660    1 11           main
0x00000000    3 97   -> 123  loc.imp._ITM_deregisterTMCloneTable

What is the name of the secret function in the example1 binary?

  • Answer: secret_func

Information

What command shows all the information about the file that you're in?

  • Answer: ia

How do you get every string that is present in the binary?

  • Answer: izz

What if you want the address of the main function?

  • Answer: im

What character do you add to the end of every command to get the output in JSON format?

  • Answer: j

How do you get the entrypoint of the file?

  • Answer: ie

What is the secret string hidden in the example2 binary?

  • Answer: goodjob

  • Steps to Reproduce:

[0x00000530]> izz
[Strings]
nth paddr      vaddr      len size section            type    string
――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――
0   0x00000034 0x00000034 4   10                      utf16le @8\t@
1   0x00000238 0x00000238 27  28   .interp            ascii   /lib64/ld-linux-x86-64.so.2
[..snip..]
80  0x00002148 0x00000882 8   8                       ascii   goodjob\n

Navigating Through Memory

How do you print out the the current memory address your located at in the binary?

  • Answer: s

What command do you use to go to a specific point in memory with the syntax?

  • Answer: s

What command would you run to go 5 bytes forward?

  • Answer: s+5

What about 12 bytes backward?

  • Answer: s-12

How do you undo the previous seek?

  • Answer: s-

How would go to the memory address of the main function?

  • Answer: s main

What if you wanted to go to the address of the rax register?

  • Answer: sr rax

Printing

How would you print the hex output of where you currently are in memory?

  • Answer: px

How would you print the disassembly of where you're currently at in memory?

  • Answer: pd

What if you wanted the disassembly of the main function?

  • Answer: pdf @ main

What command prints out the emoji hexdump? (this is not useful at all I just find it funny)

  • Answer: pxe

What if you decided you were too good for rows and you wanted the disassembly in column format?

  • Answer: pC

What is the value of the first variable in the main function for the example 3 binary?

  • Answer: 1

  • Steps to Reproduce:

    • Value 1 is being moved to var_4h:

0x00000530]> pdf @main
            ; DATA XREF from entry0 @ 0x54d
┌ 25: int main (int argc, char **argv, char **envp);
│           ; var int64_t var_8h @ rbp-0x8
│           ; var int64_t var_4h @ rbp-0x4
│           0x00000660      55             pushq %rbp
│           0x00000661      4889e5         movq %rsp, %rbp
│           0x00000664      c745fc010000.  movl $1, var_4h
│           0x0000066b      c745f8050000.  movl $5, var_8h
│           0x00000672      b800000000     movl $0, %eax
│           0x00000677      5d             popq %rbp
└           0x00000678      c3             retq

What about the second variable?

  • Answer: 5

  • Steps to Reproduce: Value 5 is being moved to var_8h

The Mid-term

How many functions are in the binary?

  • Answer: 13

  • Steps to Reproduce:

[0x00000530]> afl
0x00000530    1 42           entry0
0x00000560    4 50   -> 44   sym.deregister_tm_clones
0x000005a0    4 66   -> 57   sym.register_tm_clones
0x000005f0    5 50           sym.__do_global_dtors_aux
0x00000520    1 6            sym.imp.__cxa_finalize
0x00000630    4 48   -> 42   entry.init0
0x000004f8    3 23           sym._init
0x000006f0    1 1            sym.__libc_csu_fini
0x00000679    1 7            sym.midterm_func
0x000006f4    1 9            sym._fini
0x00000680    1 11           sym.secret_func
0x00000690    4 93           sym.__libc_csu_init
0x00000660    1 25           main
0x00000000    3 97   -> 123  loc.imp._ITM_deregisterTMCloneTable

What is the value of the hidden string?

  • Answer: you_found_me

  • Steps to Reproduce:

[0x00000530]> izz
[Strings]
nth paddr      vaddr      len size section   type    string
―――――――――――――――――――――――――――――――――――――――――――――――――――――――――――
0   0x00000034 0x00000034 4   10             utf16le @8\t@
1   0x00000238 0x00000238 27  28   .interp   ascii   /lib64/ld-linux-x86-64.so.2
2   0x00000361 0x00000361 9   10   .dynstr   ascii   libc.so.6
[..snip..]
82  0x00002178 0x00000887 14  14             ascii   \nyou_found_me\n

What is the return value of secret_func()?

  • Answer: 4

  • Steps to Reproduce:

[0x00000530]> pdf @ sym.secret_func
┌ 11: sym.secret_func ();
│           0x00000680      55             pushq %rbp
│           0x00000681      4889e5         movq %rsp, %rbp
│           0x00000684      b804000000     movl $4, %eax
│           0x00000689      5d             popq %rbp
└           0x0000068a      c3             retq

What is the value of the first variable set in the main function(in decimal format)?

  • Answer: 12

  • Steps to Reproduce: Hex 0xc -> Decimal 12

[0x00000530]> pdf @main
            ; DATA XREF from entry0 @ 0x54d
┌ 25: int main (int argc, char **argv, char **envp);
│           ; var int64_t var_8h @ rbp-0x8
│           ; var int64_t var_4h @ rbp-0x4
│           0x00000660      55             pushq %rbp
│           0x00000661      4889e5         movq %rsp, %rbp
│           0x00000664      c745fc0c0000.  movl $0xc, var_4h
│           0x0000066b      c745f8c00000.  movl $0xc0, var_8h
│           0x00000672      b800000000     movl $0, %eax
│           0x00000677      5d             popq %rbp
└           0x00000678      c3             retq

What about the second one(also in decimal format)?

  • Answer: 192

  • Steps to Reproduce: Hex 0xc0 -> Decimal 192

What is the next function in memory after the main function?

  • Answer: midterm_func

  • Steps to Reproduce:

    • Look at the next memory after main function.

    • First column denotes the memory locations

    • After 0x00000660 (main), the next function location is 0x00000679 (sym.midterm_func)

[0x00000530]> afl
0x00000530    1 42           entry0
0x00000560    4 50   -> 44   sym.deregister_tm_clones
0x000005a0    4 66   -> 57   sym.register_tm_clones
0x000005f0    5 50           sym.__do_global_dtors_aux
0x00000520    1 6            sym.imp.__cxa_finalize
0x00000630    4 48   -> 42   entry.init0
0x000004f8    3 23           sym._init
0x000006f0    1 1            sym.__libc_csu_fini
0x00000679    1 7            sym.midterm_func
0x000006f4    1 9            sym._fini
0x00000680    1 11           sym.secret_func
0x00000690    4 93           sym.__libc_csu_init
0x00000660    1 25           main
0x00000000    3 97   -> 123  loc.imp._ITM_deregisterTMCloneTable

How do you get a hexdump of four bytes of the memory address your currently at?

  • Answer: px 4

Debugging

How do you set a breakpoint?

  • Answer: db

What command is used to print out the values of all the registers?

  • Answer: dr

How do you run through the program until the program either ends or you hit the next breakpoint?

  • Answer: dc

What if you want to step through the binary one line at a time?

  • Answer: ds

How do you go forth 2 lines in the binary?

  • Answer: ds 2

How do you list out the indexes and memory addresses of all breakpoints?

  • Answer: dbi

Visual mode

How do you enter "graph mode" which allows everything to be organized in nice readable boxes

  • Answer: vV

What character do you press to run normal radare commands inside visual mode?

  • Answer: :

How do you go back to the regular radare shell(leaving visual mode)?

  • Answer: q

What if you want to step through the binary inside Visual mode?

  • Answer: s

How do you add a comment?

  • Answer: ;

Write Mode

How do you write a string to the current memory address.

  • Answer: w

What command lists all write changes?

  • Answer: wc

What command modifies an instruction at the current memory address?

  • Answer: wa

The Final Exam

What is the password that outputs the you win! message?

  • Answer: oekZ_Z_j

  • Steps to Reproduce:

    • If youdidit was compared with youdidit, then the message must be printed.

    • But the value in the user input seems to be changed at the breakpoint (at strcmp)

    [0x7f9a10920090]> pdf @main
            ; DATA XREF from entry0 @ 0x559ffa2006bd
┌ 102: int main (int argc, char **argv, char **envp);
│           ; var int64_t var_11h @ rbp-0x11
│           ; var int64_t var_8h @ rbp-0x8
│           0x559ffa200835      55             push rbp
│           0x559ffa200836      4889e5         mov rbp, rsp
│           0x559ffa200839      4883ec20       sub rsp, 0x20
│           0x559ffa20083d      488b150c0820.  mov rdx, qword [reloc.stdin] ; [0x559ffa401050:8]=0
│           0x559ffa200844      488d45ef       lea rax, [var_11h]
│           0x559ffa200848      be09000000     mov esi, 9
│           0x559ffa20084d      4889c7         mov rdi, rax
│           0x559ffa200850      e80bfeffff     call sym.imp.fgets      ; char *fgets(char *s, int size, FILE *stream)
│           0x559ffa200855      488d45ef       lea rax, [var_11h]
│           0x559ffa200859      4889c7         mov rdi, rax
│           0x559ffa20085c      e86fffffff     call sym.get_password
│           0x559ffa200861      488945f8       mov qword [var_8h], rax
│           0x559ffa200865      488b45f8       mov rax, qword [var_8h]
│           0x559ffa200869      488d35a40000.  lea rsi, str.youdidit   ; 0x559ffa200914 ; "youdidit"
│           0x559ffa200870      4889c7         mov rdi, rax
│           0x559ffa200873      e8f8fdffff     call sym.imp.strcmp     ; int strcmp(const char *s1, const char *s2)
│           0x559ffa200878      85c0           test eax, eax
│       ┌─< 0x559ffa20087a      7518           jne 0x559ffa200894
│       │   0x559ffa20087c      488d359a0000.  lea rsi, str.You_win_   ; 0x559ffa20091d ; "You win!"
│       │   0x559ffa200883      488d3d9c0000.  lea rdi, [0x559ffa200926] ; "%s"
│       │   0x559ffa20088a      b800000000     mov eax, 0
│       │   0x559ffa20088f      e8bcfdffff     call sym.imp.printf     ; int printf(const char *format)
│       └─> 0x559ffa200894      b800000000     mov eax, 0
│           0x559ffa200899      c9             leave
└           0x559ffa20089a      c3             ret
[0x7f9a10920090]> db 0x559ffa200873
[0x7f9a10920090]> dc
youdidit
hit breakpoint at: 0x559ffa200873
[0x559ffa200873]> dr
rax = 0x559ffac296b0
rbx = 0x00000000
rcx = 0x559ffac296c0
rdx = 0x559ffac296b7
r8 = 0x559ffac296b0
r9 = 0x7f9a108fbbe0
r10 = 0xfffffffffffff28d
r11 = 0x00000020
r12 = 0x559ffa2006a0
r13 = 0x00000000
r14 = 0x00000000
r15 = 0x00000000
rsi = 0x559ffa200914
rdi = 0x559ffac296b0
rsp = 0x7ffd5d05f350
rbp = 0x7ffd5d05f370
rip = 0x559ffa200873
rflags = 0x00000202
orax = 0xffffffffffffffff

    • Registers having different value (even on entering youdidit) as input:

    [0x559ffa200873]> px 8 @ 0x559ffa200914
- offset -       0 1  2 3  4 5  6 7  8 9  A B  C D  E F  0123456789ABCDEF
0x559ffa200914  796f 7564 6964 6974                      youdidit                                                                     
[0x559ffa200873]> px 8 @ 0x559ffac296b0
- offset -       0 1  2 3  4 5  6 7  8 9  A B  C D  E F  0123456789ABCDEF
0x559ffac296b0  8379 7f6e 736e 737e                      .y.nsns~

    • By performing hex subtraction:

    83797f6e736e737e − 796f756469646974 = a0a0a0a0a0a0a0a

    • So we need to subtract the value a0a0a0a0a0a0a0a from the original hex value of youdidit:

    796f756469646974 − a0a0a0a0a0a0a0a = 6f656b5a5f5a5f6a

    • Convert the hex value 6f656b5a5f5a5f6a to ascii:

    $ echo 6f656b5a5f5a5f6a | xxd -r -p
oekZ_Z_j

    • Run the binary to verify the password:

    $ ./the_final_exam 
oekZ_Z_j
You win!
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