The TIFFFetchNormalTag function in LibTiff 4.0.6 allows remote attackers to cause a denial of service (NULL pointer dereference and crash) by setting the tags TIFF_SETGET_C16ASCII or TIFF_SETGET_C32_ASCII to values that access 0-byte arrays.  NOTE: this vulnerability exists because of an incomplete fix for CVE-2016-9297.