Integer signedness error in the dissect_mount_dirpath_call function in epan/dissectors/packet-mount.c in the Mount dissector in Wireshark 1.6.x before 1.6.14 and 1.8.x before 1.8.6, when nfs_file_name_snooping is enabled, allows remote attackers to cause a denial of service (application crash) via a negative length value.