Permissions, Privileges, and Access Controls
The isURLInPortal method in the URLTool class in in_portal.py in Plone 2.1 through 4.1, 4.2.x through 4.2.5, and 4.3.x through 4.3.1 treats URLs starting with a space as a relative URL, which allows remote attackers to bypass the allow_external_login_sites filtering property, redirect users to arbitrary web sites, and conduct phishing attacks via a space before a URL in the "next" parameter to acl_users/credentials_cookie_auth/require_login.
CWE-264 - Permissions Privileges and Access Controls
CWE 264 (permissions, privileges, and access controls) is not a weakness in and of itself, rather it is a category of weaknesses related to the management of permissions, privileges, and other security features used to perform access control. If not addressed, the weaknesses in this category allow attackers to gain privileges for an unintended sphere of control, access sensitive information, and execute arbitrary commands.