In LibTIFF 4.0.9, there is a NULL pointer dereference in the TIFFWriteDirectorySec function in tif_dirwrite.c that will lead to a denial of service attack, as demonstrated by tiffset.
http://lists.opensuse.org/opensuse-security-announce/2019-04/msg00041.html
http://packetstormsecurity.com/files/155095/Slackware-Security-Advisory-libtiff-Updates.html
https://lists.debian.org/debian-lts-announce/2019/02/msg00026.html
https://seclists.org/bugtraq/2019/Nov/5
https://security.gentoo.org/glsa/202003-25