UltraVNC revision 1211 has multiple improper null termination vulnerabilities in VNC server code, which result in out-of-bound data being accessed by remote users. This attack appears to be exploitable via network connectivity. These vulnerabilities have been fixed in revision 1212.
cert-portal.siemens.com/productcert/pdf/ssa-286838.pdf
cert-portal.siemens.com/productcert/pdf/ssa-927095.pdf
cert-portal.siemens.com/productcert/pdf/ssa-940818.pdf
ics-cert.kaspersky.com/advisories/klcert-advisories/2019/03/01/klcert-19-022-ultravnc-improper-null-termination/
us-cert.cisa.gov/ics/advisories/icsa-21-131-11
www.us-cert.gov/ics/advisories/icsa-20-161-06