Software Engineering Institute

CWE-16: Configuration - CVE-2016-5673

UltraVNC repeater acts as a proxy to route remote desktop VNC connections. IP addresses are not restricted in default configurations, and ports cannot be selectively restricted. Consequently, in a default installation, a repeater can be caused to initiate connections to arbitrary hosts using any port. To initiate a connection to a common web service, for instance, an attacker may request a connection to <IP>::<80><padding>, where padding consists of null bytes and the request length is 250 bytes.

A remote, unauthenticated attacker may induce a default-configured repeater to initiate connections to arbitrary hosts and services.

Update repeater configuration

New installations of UltraVNC repeater now default to restricting access to all IP addresses and support more granular port restrictions. Existing installations should consider updating to ultravnc_repeater_1300, review the vendor's advisory, and make modifications as appropriate:

"WARNING:  In MODE I the repeater works like a proxy.  If you don't limit the destination and or ports your repeater can be used to connect to all ip adresses and all ports that can be reached from the repeater.

You need to restrict the ip addreses and ports to prevent unwanted access."