The showHelp() function in Microsoft Internet Explorer 5.01, 5.5, and 6.0 supports certain types of pluggable protocols that allow remote attackers to bypass the cross-domain security model and execute arbitrary code, aka "Improper Cross Domain Security Validation with ShowHelp functionality."
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A57
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2003/ms03-004
http://www.securityfocus.com/bid/6780
http://www.kb.cert.org/vuls/id/400577
http://www.iss.net/security_center/static/11259.php
http://www.ciac.org/ciac/bulletins/n-038.shtml
http://archives.neohapsis.com/archives/bugtraq/2003-02/0083.html