Integer overflow in ICO loader causes remote denial of service and permits remote code execution via heap buffer overflow

Summary

The ICO loader allocates data_size + BMP_FILE_HEADER_LEN bytes after reading a 32-bit attacker-controlled data_size. For data_size > UINT32_MAX - BMP_FILE_HEADER_LEN, the addition wraps before allocation. imgproxy then writes the ICO prefix and reads up to the original declared size starting 14 bytes into the undersized allocation. A network client can turn this heap overflow into remote denial of service or remote code execution.

Technical details

The vulnerable path is in vips/icoload.c at commit f4fedbb:

uint32_t data_size = GUINT32_FROM_LE(largest_image_header.data_size);

VipsPel *data = (VipsPel *) VIPS_MALLOC(NULL, data_size + BMP_FILE_HEADER_LEN);
void *actual_data = data + BMP_FILE_HEADER_LEN;

if (vips_foreign_load_read_full(ico->source, actual_data, data_size) <= 0) {
  vips_error("vips_foreign_load_ico_header", "unable to read ICO image data from the source");
  return -1;
}

The crafted directory entry contains:

data_size       = 0xfffffff5 (4294967285)
data_offset     = 22
BMP header size = 14
32-bit result   = (0xfffffff5 + 14) mod 2^32 = 3

The allocation is therefore three bytes. actual_data points 14 bytes after the allocation base. The fixture contains 64 bytes after the ICO header, so the source callback copies those 64 bytes to an invalid destination before it can report that the declared multi-…