[FD] C & C++ for OS - Filter Bypass & Persistent Vulnerability

[Vulnerability Lab <research@xxxxxxxxxxxxxxxxxxxxx>]

Document Title:
===============
C & C++ for OS - Filter Bypass & Persistent Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=1825


Release Date:
=============
2016-04-14


Vulnerability Laboratory ID (VL-ID):
====================================
1825


Common Vulnerability Scoring System:
====================================
3.5


Product & Service Introduction:
===============================
This is an ios c app,you can learn,run,share c code. The software is a offline 
compiler for developers with apple iOS.
Code templates,the contents of the new file is copy from contents of the 
template file.

(Copy of the Homepage: 
https://itunes.apple.com/us/app/c-for-os-programming-language/id1016290003 )


This is an ios c/c++ app,you can learn,run,share c/c++ code. In(the built-in 
browser or the txt editor),Select the text to run.
Code templates,the contents of the new file is copy from contents of the 
template file. 

(Copy of the Homepage: 
https://itunes.apple.com/us/app/c-c++-offline-compiler-for/id1016322367 )


Abstract Advisory Information:
==============================
The vulnerability laboratory core research team discovered an application-side 
validation vulnerability in the official C & C++ for OS web-application (api).


Vulnerability Disclosure Timeline:
==================================
2016-04-14: Public Disclosure (Vulnerability Laboratory)


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


Affected Product(s):
====================
XiaoWen Huang
Product: C for OS & C++ - Mobile API (Web-Application) 1.2


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


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


Technical Details & Description:
================================
A persistent input validation and mail encode web vulnerability has been 
discovered  in the official C & C++ for OS web-application (api).
The persistent web vulnerability allows an attacker to inject malicious script 
codes on the application-side of the vulnerable modules context.

The basic validation of the code formular and mask allows to include any type 
of script codes or programming language without offensive input 
restrictions. Attackers can inject code to a project to share it with another 
source. In the moment the code of the project is generated to as 
email body, a persistent script code execution occurs.

There are two options to exploit, first is to send the malicious mail to the 
author of the program by the `Mail Author` function. Another possibility 
to execute code in the email body context is to share it with another code 
editor by email. In both email body message context the injected wrong 
filtered script code execution occurs. The internal encoding of the formular is 
correctly done but in case of sharing by qr or via message body email 
the execution occurs. The vulnerability is located on the application-side of 
the iOS application and the request method to inject requires physical 
device access or access to the share function. The bug is present in the C & 
C++ for OS 1.2 version of the mobile client. Attackers can for example 
generate a QR code with malicious context that is executed in the message body 
were the code is mainly displayed by the iOS application.

The security risk of the application-side vulnerability is estimated as medium 
with a cvss (common vulnerability scoring system) count of 3.5. 
Exploitation of the persistent vulnerability requires a low privileged ios 
device user account with restricted access and low user interaction. 
Successful exploitation of the vulnerabilities results in persistent phishing 
mails, session hijacking, persistent external redirect to malicious 
sources and application-side manipulation of affected or connected module 
context.

Vulnerable Module(s):
                                [+] Share to Authors
                                [+] Share by Email
                                [+] Share via QR Code

Vulnerable Function(s):
                                [+] Console
                                [+] C  or C++


Proof of Concept (PoC):
=======================
The persistent vulnerability and mail encoding bug can be exploited by remote 
attackers with low privileged device user account and low user interaction.
For security demonstration or to reproduce the vulnerability follow the 
provided information and steps below to continue.

Manual steps to reproduce the vulnerability ...
1. Install the perl app to your apple iOS device
2. Start the mobile application
3. Include to the first variable in the demo code java or html script code and 
save the entry as c or c++ script
4. Open the saved entry again and click the top right arrow menu
5. Now choose Create QR or Share menu button
6. Open the menu `Mail to Author` or push the default `iOS Mail App` button
7. Now the code of the formular gets transfered to the email message body 
context
Note: The encoding does not parse or encode any inserted values
8. The email arrives to the target inbox
9. Open the email and the code executes directly in the message body or next to 
the generated qr code
10. Successful reproduce of the filter and validation vulnerability in the c 
and c++ app api!

Note: The bug can be exploited by sending to the author, by sending to another 
target mail or by transfer of a qr code.


Solution - Fix & Patch:
=======================
The vulnerability can be patched by a secure parse and encode of the vulnerable 
message body context.
Filter and parse all code values that are included to the message body. 
Configure the code to plain text not html to prevent 
further persistent injection attacks. In case of emergency use the escape 
function to separate the mechanism permanently.


Security Risk:
==============
The security risk of the application-side mail encode web vulnerability in the 
mobile application api is estimated as medium. (CVSS 3.5)


Credits & Authors:
==================
Vulnerability Laboratory [Research Team] - Benjamin Kunz Mejri 
(bkm@xxxxxxxxxxxxxxxxx) [www.vulnerability-lab.com]


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