static void php_var_serialize_class(smart_str *buf, zval *struc, zval *retval_ptr, php_serialize_data_t var_hash) /* {{{ */
{
	uint32_t count;
	zend_bool incomplete_class;
	HashTable *ht;

	incomplete_class = php_var_serialize_class_name(buf, struc);
	/* count after serializing name, since php_var_serialize_class_name
	 * changes the count if the variable is incomplete class */
	if (Z_TYPE_P(retval_ptr) == IS_ARRAY) {
		ht = Z_ARRVAL_P(retval_ptr);
		count = zend_array_count(ht);
	} else if (Z_TYPE_P(retval_ptr) == IS_OBJECT) {
		ht = Z_OBJPROP_P(retval_ptr);
		count = zend_array_count(ht);
		if (incomplete_class) {
			--count;
		}
	} else {
		count = 0;
		ht = NULL;
	}

	if (count > 0) {
		zval *d;
		zval nval, *nvalp;
		zend_string *name;
		HashTable *names, *propers;

		names = php_var_serialize_collect_names(ht, count, incomplete_class);

		smart_str_append_unsigned(buf, zend_hash_num_elements(names));
		smart_str_appendl(buf, ":{", 2);

		ZVAL_NULL(&nval);
		nvalp = &nval;
		propers = Z_OBJPROP_P(struc);

		ZEND_HASH_FOREACH_STR_KEY(names, name) {
			if ((d = zend_hash_find(propers, name)) != NULL) {
				if (Z_TYPE_P(d) == IS_INDIRECT) {
					d = Z_INDIRECT_P(d);
					if (Z_TYPE_P(d) == IS_UNDEF) {
						continue;
					}
				}
				php_var_serialize_string(buf, ZSTR_VAL(name), ZSTR_LEN(name));
				php_var_serialize_intern(buf, d, var_hash);
			} else {
				zend_class_entry *ce = Z_OBJ_P(struc)->ce;
				if (ce) {
					zend_string *prot_name, *priv_name;

					do {
						priv_name = zend_mangle_property_name(
								ZSTR_VAL(ce->name), ZSTR_LEN(ce->name), ZSTR_VAL(name), ZSTR_LEN(name), ce->type & ZEND_INTERNAL_CLASS);
						if ((d = zend_hash_find(propers, priv_name)) != NULL) {
							if (Z_TYPE_P(d) == IS_INDIRECT) {
								d = Z_INDIRECT_P(d);
								if (Z_ISUNDEF_P(d)) {
									break;
								}
							}
							php_var_serialize_string(buf, ZSTR_VAL(priv_name), ZSTR_LEN(priv_name));
							zend_string_free(priv_name);
							php_var_serialize_intern(buf, d, var_hash);
							break;
						}
						zend_string_free(priv_name);
						prot_name = zend_mangle_property_name(
								"*", 1, ZSTR_VAL(name), ZSTR_LEN(name), ce->type & ZEND_INTERNAL_CLASS);
						if ((d = zend_hash_find(propers, prot_name)) != NULL) {
							if (Z_TYPE_P(d) == IS_INDIRECT) {
								d = Z_INDIRECT_P(d);
								if (Z_TYPE_P(d) == IS_UNDEF) {
									zend_string_free(prot_name);
									break;
								}
							}
							php_var_serialize_string(buf, ZSTR_VAL(prot_name), ZSTR_LEN(prot_name));
							zend_string_free(prot_name);
							php_var_serialize_intern(buf, d, var_hash);
							break;
						}
						zend_string_free(prot_name);
						php_var_serialize_string(buf, ZSTR_VAL(name), ZSTR_LEN(name));
						php_var_serialize_intern(buf, nvalp, var_hash);
						php_error_docref(NULL, E_NOTICE,
								"\"%s\" returned as member variable from __sleep() but does not exist", ZSTR_VAL(name));
					} while (0);
				} else {
					php_var_serialize_string(buf, ZSTR_VAL(name), ZSTR_LEN(name));
					php_var_serialize_intern(buf, nvalp, var_hash);
				}
			}
		} ZEND_HASH_FOREACH_END();
		smart_str_appendc(buf, '}');

		zend_hash_destroy(names);
		FREE_HASHTABLE(names);
	} else {
		smart_str_appendl(buf, "0:{}", 4);
	}
}
/* }}} */

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.