RealVNC 4.1.1, and other products that use RealVNC such as AdderLink IP and Cisco CallManager, allows remote attackers to bypass authentication via a request in which the client specifies an insecure security type such as "Type 1 - None", which is accepted even if it is not offered by the server, as originally demonstrated using a long password.
https://exchange.xforce.ibmcloud.com/vulnerabilities/26445
http://www.vupen.com/english/advisories/2006/2492
http://www.vupen.com/english/advisories/2006/1821
http://www.vupen.com/english/advisories/2006/1790
http://www.securityfocus.com/bid/17978
http://www.securityfocus.com/archive/1/438368/100/0/threaded
http://www.securityfocus.com/archive/1/438175/100/0/threaded
http://www.securityfocus.com/archive/1/434560/100/0/threaded
http://www.securityfocus.com/archive/1/434518/100/0/threaded
http://www.securityfocus.com/archive/1/434117/100/0/threaded
http://www.securityfocus.com/archive/1/434015/100/0/threaded
http://www.securityfocus.com/archive/1/433994/100/0/threaded
http://www.realvnc.com/products/free/4.1/release-notes.html
http://www.kb.cert.org/vuls/id/117929
http://www.intelliadmin.com/blog/2006/05/vnc-flaw-proof-of-concept.html
http://www.intelliadmin.com/blog/2006/05/security-flaw-in-realvnc-411.html
http://www.cisco.com/warp/public/707/cisco-sr-20060622-cmm.shtml
http://securitytracker.com/id?1016083
http://securityreason.com/securityalert/8355
http://secunia.com/advisories/20789
http://secunia.com/advisories/20109
http://secunia.com/advisories/20107
http://seclists.org/fulldisclosure/2022/May/29