The "You are not allowed..." error handler in XWiki 1.0 B1 and 1.0 B2 associates the doc variable with the entire document content and metadata regardless of a user's view rights, which allows remote authenticated users to read arbitrary documents via a custom skin that prints the content attribute of the doc variable.
The search functionality in XWiki 0.9.793 indexes cleartext user passwords, which allows remote attackers to obtain sensitive information via a search string that matches a password.