TightVNC before 1.2.6 generates the same challenge string for multiple connections, which allows remote attackers to bypass VNC authentication by sniffing the challenge and response of other users.
https://exchange.xforce.ibmcloud.com/vulnerabilities/5992
http://www.tightvnc.com/WhatsNew.txt
http://www.securityfocus.com/bid/5296
http://www.redhat.com/support/errata/RHSA-2003-041.html
http://www.redhat.com/support/errata/RHSA-2002-287.html
http://www.mandrakesoft.com/security/advisories?name=MDKSA-2003:022
http://marc.info/?l=bugtraq&m=102769183913594&w=2
http://marc.info/?l=bugtraq&m=102753170201524&w=2
http://distro.conectiva.com.br/atualizacoes/?id=a&anuncio=000640