LibVNC before 0.9.12 contains multiple heap out-of-bounds write vulnerabilities in libvncclient/rfbproto.c. The fix for CVE-2018-20019 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/e34bcbb759ca5bef85809967a268fdf214c1ad2c
https://github.com/LibVNC/libvncserver/commit/c5ba3fee85a7ecbbca1df5ffd46d32b92757bc2a
https://github.com/LibVNC/libvncserver/commit/c2c4b81e6cb3b485fb1ec7ba9e7defeb889f6ba7
https://github.com/LibVNC/libvncserver/commit/a64c3b37af9a6c8f8009d7516874b8d266b42bae
https://cert-portal.siemens.com/productcert/pdf/ssa-390195.pdf