A weakness and multiple vulnerabilities have been discovered in ownCloud, which can be exploited by malicious users to compromise a vulnerable system and by malicious people to conduct spoofing, cross-site scripting, and cross-site request forgery attacks.

1) Input passed via the "redirect_url" parameter to index.php is not properly verified before being used to redirect users. This can be exploited to redirect a user to an arbitrary website e.g. when a user clicks a specially crafted link to the affected script hosted on a trusted domain.

2) Input passed via the "redirect_url" parameter to index.php and the "files" parameter to files/ajax/download.php is not properly sanitised before being returned to the user. This can be exploited to execute arbitrary HTML and script code in a user's browser session in context of an affected site.

3) The application allows users to perform certain actions via HTTP requests without performing proper validity checks to verify the requests. This can be exploited to e.g. conduct script insertion attacks via editing contacts when a logged-in user visits a specially crafted web page.

4) An error due to the files/ajax/upload.php script not verifying the extension of an uploaded file can be exploited to e.g. upload an .htaccess file, which will allow uploaded PHP files to be executed.

The weakness and vulnerabilities are confirmed in version 3.0.2. Other versions may also be affected.

Solution
Vulnerability #4 is fixed in the GIT repository. Edit the source code to ensure that input is properly sanitised and verified. Do not browse untrusted sites or follow untrusted links while being logged-in to the application.

Provided and/or discovered by
1-3) Tobias Glemser, Tele-Consulting.
4) luks

Changelog
Further details available to Secunia VIM customers

Original Advisory
ownCloud:
http://gitorious.org/owncloud/owncloud/commit/acdce2b1e01f7c0a77b7e7949540e1b0ba94efd1

Tele-Consulting:
http://www.tele-consulting.com/advisories/TC-SA-2012-01.txt

luks:
http://seclists.org/fulldisclosure/2012/Apr/223

Deep Links
Links available to Secunia VIM customers