LibVNC before 0.9.12 contains a heap out-of-bounds write vulnerability in libvncserver/rfbserver.c. The fix for CVE-2018-15127 was incomplete.
https://www.openwall.com/lists/oss-security/2018/12/10/8
https://usn.ubuntu.com/4587-1/
https://usn.ubuntu.com/4547-1/
https://usn.ubuntu.com/3877-1/
https://lists.debian.org/debian-lts-announce/2019/10/msg00042.html
https://lists.debian.org/debian-lts-announce/2019/01/msg00029.html
https://github.com/LibVNC/libvncserver/issues/273
https://github.com/LibVNC/libvncserver/commit/15bb719c03cc70f14c36a843dcb16ed69b405707
https://cert-portal.siemens.com/productcert/pdf/ssa-390195.pdf