ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), statically linked, stripped Check with strings :
25 73 12 45 9A 34 22 11 ... – that’s the encrypted flag. Write a simple emulator in Python to trace execution without actually running the binary.
The VM initializes reg0 as the bytecode length, reg1 as the starting address of encrypted flag. The flag is likely embedded as encrypted bytes in the VM’s memory[] . In the binary, locate the .rodata section – there’s a 512-byte chunk starting at 0x804B040 containing the bytecode + encrypted data. f1vm 32 bit
f1vm_32bit (ELF 32-bit executable) 2. Initial Analysis file f1vm_32bit Output:
dd if=f1vm_32bit of=bytecode.bin bs=1 skip=$((0x804B040)) count=256 Using xxd : ELF 32-bit LSB executable, Intel 80386, version 1
strings f1vm_32bit | grep -i flag No direct flag. But there’s a section: [+] Flag is encrypted in VM memory.
Run the binary:
./f1vm_32bit Output:
00000000: 01 01 00 00 00 40 mov reg1, 0x40000000 00000006: 10 01 push reg1 ... At offset 0x80 inside the bytecode, there’s a sequence: The VM initializes reg0 as the bytecode length,
| Opcode | Mnemonic | Operands | |--------|--------------|-------------------------| | 0x01 | MOV reg, imm | reg (1 byte), imm (4 bytes) | | 0x02 | ADD reg, reg | src, dst | | 0x03 | XOR reg, reg | | | 0x10 | PUSH reg | | | 0x11 | POP reg | | | 0x20 | JMP addr | 4-byte address | | 0x21 | JZ addr | jump if reg0 == 0 | | 0xFF | HALT | |
while (1) opcode = memory[pc++]; switch(opcode) case 0x01: // MOV reg, imm case 0x02: // ADD case 0x03: // XOR ...