There are 3 open security issues in buster.
1 issue left for the package maintainer to handle:
A divide by zero issue was found to occur in libvncserver-0.9.12. A malicious client could use this flaw to send a specially crafted message that, when processed by the VNC server, would lead to a floating point exception, resulting in a denial of service.
You can find information about how to handle this issue in the security team's documentation.
2 ignored issues:
It was discovered that websockets.c in LibVNCServer prior to 0.9.12 did not properly decode certain WebSocket frames. A malicious attacker could exploit this by sending specially crafted WebSocket frames to a server, causing a heap-based buffer overflow.
An issue was discovered in LibVNCServer before 0.9.13. An improperly closed TCP connection causes an infinite loop in libvncclient/sockets.c.