Internet Explorer 5.5 and 5.01 allows remote attackers to bypass security restrictions via malformed URLs that contain dotless IP addresses, which causes Internet Explorer to process the page in the Intranet Zone, which may have fewer security restrictions, aka the "Zone Spoofing vulnerability."

References

• https://nvd.nist.gov/vuln/detail/CVE-2001-0664
• https://docs.microsoft.com/en-us/security-updates/securitybulletins/2001/ms01-051
• https://exchange.xforce.ibmcloud.com/vulnerabilities/7258
• http://marc.info/?l=bugtraq&m=100281551611595&w=2
• http://morph3us.org/blog/?p=31
• http://www.osvdb.org/1971
• http://www.securityfocus.com/bid/3420