int mif_validate(jas_stream_t *in)
{
	uchar buf[MIF_MAGICLEN];
	uint_fast32_t magic;
	int i;
	int n;

	assert(JAS_STREAM_MAXPUTBACK >= MIF_MAGICLEN);

	/* Read the validation data (i.e., the data used for detecting
	  the format). */
	if ((n = jas_stream_read(in, buf, MIF_MAGICLEN)) < 0) {
		return -1;
	}

	/* Put the validation data back onto the stream, so that the
	  stream position will not be changed. */
	for (i = n - 1; i >= 0; --i) {
		if (jas_stream_ungetc(in, buf[i]) == EOF) {
			return -1;
		}
	}

	/* Was enough data read? */
	if (n < MIF_MAGICLEN) {
		return -1;
	}

	/* Compute the signature value. */
	magic = (buf[0] << 24) | (buf[1] << 16) | (buf[2] << 8) | buf[3];

	/* Ensure that the signature is correct for this format. */
	if (magic != MIF_MAGIC) {
		return -1;
	}

	return 0;
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.