Explore the basics of cybersecurity in the Nostalgia Challenge on Hack The Box. This medium-level Challenge introduces encryption reversal and file handling concepts in a clear and accessible way, perfect for beginners.

https://app.hackthebox.com/challenges/122

Description#

It’s late at night and your room’s a mess, you stumble upon an dusty old looking box and you decide to go through it, you start unveiling hidden childhood memories and you find a mesmerising gamebody advanced flash card labeled “Nostalgia”, you pop the card in and a logo welcomes you, this strange game expects you to input a cheatcode. Can you figure it out?

Exploitation#

Using mgba#

Launch the game with mgba Nostalgia.gba -g and connect to GDB using gdb -ex="target remote localhost:2345". Enter the sequence Left Left Z X X X Enter in the game window to reveal the flag.

Using no$gba Debugger#

Install no$gba with nocashgba-debuggerand open the ROM. Enter Any arrows 8 times Set a breakpoint at 0200162A cmp r0,4h and press Ctrl in the program window to set r0 = 4h.

When the program reaches 0200162C beq 020016F0 clicking Run Next, change the Z flag to make the branch false. Continue to 02001630 bne 2001660h and change Z again.

At 02001636 cmp r3,0F3h and 0200163B bne 200161Eh, change Z to false one last time. Press [F9] to run the program, and the flag will appear in the game window.

Summary#

The Nostalgia Challenge involves exploiting a Game Boy Advance ROM. Using mgba, you can input a specific sequence of controls to reveal the flag. Alternatively, with no$gba debugger, the challenge demonstrates low-level debugging techniques by manipulating CPU flags (Z) to alter the program flow and ultimately reveal the flag in the game window.