The vncserver wrapper for vnc before 3.3.3r2-21 uses the rand() function instead of srand(), which causes vncserver to generate weak cookies.
http://www.securityfocus.com/bid/6905
http://www.redhat.com/support/errata/RHSA-2003-068.html
http://www.redhat.com/support/errata/RHSA-2003-041.html
http://www.mandrakesoft.com/security/advisories?name=MDKSA-2003:022
http://www.iss.net/security_center/static/11384.php
http://sunsolve.sun.com/pub-cgi/retrieve.pl?doc=fsalert/56161
http://security.gentoo.org/glsa/glsa-200302-15.xml
http://distro.conectiva.com.br/atualizacoes/?id=a&anuncio=000640
http://changelogs.credativ.org/debian/pool/main/v/vnc/vnc_3.3.6-3/changelog