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Bashi v1.6 iOS - Persistent Mail Encoding Vulnerability



Document Title:
===============
Bashi v1.6 iOS - Persistent Mail Encoding Vulnerability


References (Source):
====================
http://www.vulnerability-lab.com/get_content.php?id=1852


Release Date:
=============
2016-05-25


Vulnerability Laboratory ID (VL-ID):
====================================
1852


Common Vulnerability Scoring System:
====================================
3.4


Product & Service Introduction:
===============================
This is an ios bash4.3 app,you can learn,run,share bash 4.3 script. Code templates,the contents of the new file is copy from 
contents of the template file. In(the built-in browser or the txt editor),Select the text to run.


Abstract Advisory Information:
==============================
The vulnerability laboratory core research team discovered an application-side mail encoding web vulnerability in the official Bashi v1.6 iOS mobile application.


Vulnerability Disclosure Timeline:
==================================
2016-05-25:	Public Disclosure (Vulnerability Laboratory)


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


Affected Product(s):
====================
XiaoWen Huang
Product: Bashi - iOS Mobile Application 1.6


Exploitation Technique:
=======================
Local


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


Technical Details & Description:
================================
An application-side input validation web vulnerability has been discovered in the official Bashi v1.6 iOS mobile application.
The security web vulnerability allows to inject malicious script codes on the application-side of the vulnerable iOS mobile app.

The vulnerability is located in the encode mechanism of the `code console` input field. Local attackers with restricted or local low 
privileged application user accounts are able to inject own malicious script codes to the code console input. Thus code can be send by 
the share function to the author or random emails. The execution of the malicious script code occurs in the mail body message context 
on sharing by email. The injection point of the vulnerability is the code console compiler input field. The attack vector of the issue 
is persistent on the application-side and the request method to inject is a basic device sync.

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 web vulnerability requires a low privileged ios device 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)
				[+] Code Console
 
Vulnerable Input(s):
				[+] Code Template

Vulnerable Parameter(s)
				[+] code

Affected Module(s)
				[+] Mail Message Body (Share Function)


Proof of Concept (PoC):
=======================
The application-side validation web vulnerability can be exploited by remote attackers with low privileged iOS device user account and without 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 vulnerable iOS app to your apple device
2. Start the app
3. Click the code module to open the compiler
4. Inject a script code payload to the "$Person" variable in the code-line input field
5. Now, click above the share button and choose send by email
Note: The payload is getting saved to the mail body message context
6. The execution occurs directly in the mail body of the email context were the code becomes via echo visible
7. Successful reproduce of the vulnerability!


PoC: Code Template - Share
<p>#Note:The&nbsp;template&nbsp;file&nbsp;will&nbsp;be&nbsp;copied&nbsp;to&nbsp;a&nbsp;new&nbsp;file.&nbsp;When&nbsp;you&nbsp;
change&nbsp;the&nbsp;code&nbsp;of&nbsp;the&nbsp;template&nbsp;file&nbsp;you&nbsp;can&nbsp;create&nbsp;new&nbsp;file&nbsp;with&
nbsp;this&nbsp;base&nbsp;code.&nbsp;<br>echo&nbsp;<iframe>What&amp;nbsp;is&amp;nbsp;your&amp;nbsp;name?';&lt;br&gt;read&amp;
nbsp;PERSON&amp;nbsp;&lt;br&gt;echo&amp;nbsp;"Hello&amp;nbsp;$PERSON";&lt;/p&gt;&lt;br&gt;&lt;br&gt; *My favorite app:&lt;
A target="_blank" href="<a href="https://itunes.apple.com/app/id936560010?mt=8";>
https://itunes.apple.com/app/id936560010</a>"&gt;bashi&lt;/A&gt;</iframe></p>


Solution - Fix & Patch:
=======================
The vulnerability can be patched by a secure parse and encode of the vulnerable `code compiler` input field. 
Restrict the input field and disallow usage of special chars.
Encode the mail message body context that is getting transfered by the code module input to the email body context.


Security Risk:
==============
The security risk of the persistent mail encoding web vulnerability in the  iOS app is estimated as medium. (CVSS 3.4)


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


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