PHP Event Calendar Multiple Parameter Cross Site Scripting Vulnerability


OS2A ID: OS2A_1007      Status:
          08/20/2006  Issue Discovered
          09/06/2006  Reported to the Vendor
          09/09/2006      Fixed by Vendor
          09/13/2006  Advisory Released
          

Class: Cross Site Scripting    Severity: Low


Overview:
---------
PHP Event Calendar is a reusable PHP script that extends a web site's
functionality with an event scheduler and/or news archive.
http://www.softcomplex.com/products/php_event_calendar/

Description:
------------
A cross-site scripting vulnerability exists in PHP Event Calendar, due to input
validation error in parameters tilte(ti), body(bi) and backgroung Image(cbgi)
in cl_files/index.php page when adding a new event.

Successful exploitation requires authentication.

Impact:
-------
An authenticated remote attacker could inject malicious HTML and script code in
other user's browser session within the security context of the affected site.

Affected Software(s):
---------------------
PHP Event Calendar 1.5.1 (prior versions may also be vulnerable)

Proof of Concept:
-----------------
http://www.yoursite.com/directory_where_you_installed_php_event_calendar/cl_files/index.php
Vulnerable fields: title field       - ti
       body field        - bi
       Backgroung Image  - cbgi 

Insert "<script>alert('XSS Vulnerable');</script>" in above field and click
"Add event".

CVSS Score Report:
-----------------
    ACCESS_VECTOR          = REMOTE
    ACCESS_COMPLEXITY      = LOW
    AUTHENTICATION         = REQUIRED
    CONFIDENTIALITY_IMPACT = NONE
    INTEGRITY_IMPACT       = PARTIAL
    AVAILABILITY_IMPACT    = NONE
    IMPACT_BIAS            = INTEGRITY
    EXPLOITABILITY         = PROOF_OF_CONCEPT
    REMEDIATION_LEVEL      = OFFICIAL_FIX
    REPORT_CONFIDENCE      = CONFIRMED
    CVSS Base Score        = 2.1 (AV:R/AC:L/Au:R/C:N/I:P/A:N/B:I)
    CVSS Temporal Score    = 1.6
    Risk factor            = Low


Vendor Response:
---------------
"Attached is the version that blocks the use of the <script> in the
text of the event. We can't block use of HTML completely because many
users want to be able to use HTML for the event descriptions. The
events are managed in the password protected control panel so there
was no security threat even before the change was applied."


Solution:
---------

Update to the fixed version,
http://www.softcomplex.com/products/php_event_calendar/

Credits:
--------
NR Nandini of OS2A has been credited with the discovery of this vulnerability.