Race condition in WinVNC

James [Wez] Weatherall jnw "at" orl.co.uk
Fri, 23 Oct 1998 16:51:19 +0000

On Thu, 22 Oct 1998, Greg Hewgill wrote:

> I have identified a race condition in the startup of WinVNC. I discovered
> this problem today when trying to connect to a machine I had just rebooted
> (WinVNC is installed as an auto-start service). I started my VNC viewer, and
> tried to connect to the server. The first time the connection was refused,
> but I tried again immediately and (much to my surprise) it let me straight
> in without even asking for a password!
> I looked at the code for the server and the problem appears to be in the
> WinVNCAppMain() function. The server.SockConnect() function is called before
> a new vncMenu object is created, which means a thread will start listening
> on the socket before the server settings are loaded (the settings are loaded
> by the vncMenu object). If the m_passwd_required field of the vncServer
> object happens to be 0 (it is not initialized), then no password will be
> required for a short time until the settings are loaded.
> I presume this could be fixed by moving the creation of the vncMenu object
> above the initialization of the two connection listeners.

Thanks for the info, Greg.  I've updated the code to correctly initialise
the value of the AuthRequired flag to TRUE, preventing unauthenticated
connections by default.

This fix is in the next release, out later today, hopefully!


James "Wez" Weatherall
Olivetti & Oracle Research Laboratory, Cambridge, UK - Tel : 343000
Laboratory for Communications Engineering, Cambridge - Tel : -

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