Internet Explorer 5.01, 5.5, and 6 allows remote attackers to spoof a less restrictive security zone and execute arbitrary code via an HTML page containing URLs that contain hostnames that have been double hex encoded, which are decoded twice to generate a malicious hostname, aka the "URL Decoding Zone Spoofing Vulnerability."
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A3586
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A3196
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A3060
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A1736
https://oval.cisecurity.org/repository/search/definition/oval%3Aorg.mitre.oval%3Adef%3A1308
https://exchange.xforce.ibmcloud.com/vulnerabilities/19214
https://docs.microsoft.com/en-us/security-updates/securitybulletins/2005/ms05-014
http://www.us-cert.gov/cas/techalerts/TA05-039A.html