eXpBlog <= 0.3.5 Cross Site Scripting Vulnerabilities

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  Advisory: eXpBlog <= 0.3.5 Cross Site Scripting Vulnerabilities

Release Date: 10/09/2006
Last Modified: 10/09/2006
Author: Tamriel [tamriel <at> gmx <dot> net]
Application: eXpBlog <= 0.3.5
Risk: Low
Vendor Status: contaced | replied
Vendor Site: www.expblog.de

Overview:

Quote from www.expblog.de:

"Das eXpBlog ist eine beliebte Freeware weBlog Software basierend
auf PHP und mySQL. Mit einem eXpBlog verfuegen Sie ueber ein
flexibles und schnelles Mehrbenutzer-weBlog welches durch ein
Plugin-System komfortabel erweiterbar ist."

There are some cross site scripting vulnerabilities which can
be exploited by malicious people to conduct script insertion attacks.

The vulnerability has been discovered in the latest version. Other
versions may also be affected.

Details:

1) Cross Site Scripting Vulnerability in kalender.php

  Arround the lines 130-140 the variable `$_SERVER['PHP_SELF']` is
  not properly sanitised before being used. This can be exploited
  to insert arbitrary HTML and script code, which is executed in a
  user's browser session in context of an affected site when the
  malicious data is viewed.

2) Cross Site Scripting Vulnerability in pre_details.php

  Arround the lines 15-20 the variable
  `$_POST["captcha_session_code"]` is not properly sanitised before
  being used. This variable is used in the details.php arround
  line 152, here an attacker can insert malicious code. The
  captcha class may be affected too, because you can let it open a
  special file (captcha_class.php, arround line 140).

Proof of Concept:

1) details.php/%3E%22%3E%3Cscript%3Ealert('Unsecure')%3C/script%3E

2) comment=1&captcha_session_code=>"><script>alert('hole')</script>…

Solution/Fix:

  Edit the source code to ensure that input is properly sanitised.
  Use functions like PHP`s htmlentities() function.

Disclosure Timeline:

  10/03/2006 - Discovery of the vulnerabilities
  10/03/2006 - Contacted the vendor
  10/04/2006 - Vendor reponse
  10/09/2006 - Supplied bugfix to the official forum
  10/09/2006 - Public disclosure

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