Vmpwn !!top!! Link

1. What is vmpwn? vmpwn is a subcategory of binary exploitation challenges where the target implements a custom virtual machine (VM) – typically a bytecode interpreter. Instead of attacking native CPU instructions, the attacker abuses flaws in the VM’s implementation: its memory layout, instruction handlers, bounds checking, or state management.

These challenges combine reverse engineering (understanding the VM’s opcodes and data structures) with classic memory corruption techniques. | Vulnerability | Description | |---------------|-------------| | OOB read/write | Index into VM memory array not validated | | Type confusion | Treating integer as pointer (e.g., storing real addresses in registers) | | Use-after-free | VM manages heap objects (strings, arrays) without proper refcounting | | Infinite loop / DoS | Control flow opcodes miss checks | | Memory leak | Uninitialized memory disclosure → bypass ASLR | | Arbitrary read/write primitive | Combining bugs to read/write anywhere in process memory | 3. Typical VM Structure (Simplified) typedef struct uint8_t *code; // bytecode size_t ip; // instruction pointer uint32_t regs[8]; // registers (may hold values or pointers) uint8_t *mem; // VM "RAM" array size_t mem_size; uint32_t stack[256]; // operand stack int sp; vm_t; Instructions often look like: