source: http://www.securityfocus.com/bid/53145/info

ownCloud is prone to a URI open-redirection vulnerability, multiple cross-site scripting vulnerabilities and multiple HTML-injection vulnerabilities because it fails to properly sanitize user-supplied input.

An attacker could leverage the cross-site scripting issues to execute arbitrary script code in the browser of an unsuspecting user in the context of the affected site. This may let the attacker steal cookie-based authentication credentials and launch other attacks.

Attacker-supplied HTML and script code would run in the context of the affected browser, potentially allowing the attacker to steal cookie-based authentication credentials or control how the site is rendered to the user. Other attacks are also possible.

Successful exploits may redirect a user to a potentially malicious site; this may aid in phishing attacks.

ownCloud 3.0.0 is vulnerable; other versions may also be affected. 

http://www.example.com/owncloud/index.php?redirect_url=1"><script>alert("Help Me")</script><l=" (must not be logged in)

http://www.example.com/owncloud/index.php?redirect_url=http%3a//www.boeserangreifer.de/