An issue was discovered in LibVNCServer before 0.9.13. libvncclient/tls_openssl.c has a NULL pointer dereference.
https://usn.ubuntu.com/4434-1/
https://github.com/LibVNC/libvncserver/compare/LibVNCServer-0.9.12...LibVNCServer-0.9.13
https://github.com/LibVNC/libvncserver/commit/33441d90a506d5f3ae9388f2752901227e430553
https://cert-portal.siemens.com/productcert/pdf/ssa-390195.pdf