reversemedium

Kitten and fl@g

hackerlab

Task: UPX-packed statically linked ELF binary (Tamagotchi game) with corrupted UPX header and a false flag in the game-win path. Solution: repaired UPX magic bytes, identified give_flag as a trap, discovered that printf was patched to call hidden __vfxsprintf function containing XOR-based flag construction verified via environment variables.

$ ls tags/ techniques/
environment_variablesxorupxanti_unpackingstatic_linkingcfunction_patchingfalse_flagelf_x86_64tamagotchi
upx_header_repairfalse_flag_identificationpatched_libc_function_analysisxor_chain_decodingoverlapping_memory_write_reconstructionenvironment_variable_flag_verification
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