Cross-site scripting (XSS) vulnerability in the UI messages functionality in Roundcube Webmail before 0.5.4 allows remote attackers to inject arbitrary web script or HTML via the _mbox parameter to the default URI.

steps/utils/modcss.inc in Roundcube Webmail before 0.5.1 does not properly verify that a request is an expected request for an external Cascading Style Sheets (CSS) stylesheet, which allows remote authenticated users to trigger arbitrary outbound TCP connections from the server, and possibly obtain sensitive information, via a crafted request.

The login form in Roundcube Webmail before 0.5.1 does not properly handle a correctly authenticated but unintended login attempt, which makes it easier for remote authenticated users to obtain sensitive information by arranging for a victim to login to the attacker's account and then compose an e-mail message, related to a "login CSRF" issue.

Roundcube 0.3.1 and earlier does not request that the web browser avoid DNS prefetching of domain names contained in e-mail messages, which makes it easier for remote attackers to determine the network location of the webmail user by logging DNS requests.