Monday, July 19, 2021

Schneider Electric EVlink Charging Stations Authentication Bypass / Code Execution

SEC Consult Vulnerability Lab Security Advisory < 20210714-0 >
=======================================================================
title: Authentication bypass & Remote code execution
product: Multiple Schneider Electric EVlink Charging Stations
vulnerable version: Firmware R7 (Version V3.3.0.15)
fixed version: Firmware R8 (Version V3.4.0.1)
CVE number: CVE-2021-22707, CVE-2021-22708
impact: Critical
homepage:https://www.se.com/ <https://www.se.com/>
found: 2021-03-08
by: Stefan Viehböck (Office Vienna)
SEC Consult Vulnerability Lab

An integrated part of SEC Consult, an Atos company
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https://www.sec-consult.com <https://www.sec-consult.com>

=======================================================================

Vendor description:
-------------------
"Our mission is to be your digital partner for Sustainability and Efficiency.
We drive digital transformation by integrating world-leading process and energy
technologies, end-point to cloud connecting products, controls, software and
services, across the entire lifecycle, enabling integrated company management,
for homes, buildings, data centers, infrastructure and industries.
We are the most local of global companies. We are advocates of open standards
and partnership ecosystems that are passionate about our shared Meaningful
Purpose, Inclusive and Empowered values."

Source:https://www.se.com/ww/en/about-us/ <https://www.se.com/ww/en/about-us/>


Business recommendation:
------------------------
The vendor provides a firmware update for the affected charging stations which
should be installed immediately.

SEC Consult highly recommends to perform a thorough security review of the
Schneider Electric EVlink product line conducted by security professionals to
identify and resolve potential further security issues.


Vulnerability overview/description:
-----------------------------------
1) Authentication Bypass with Undocumented Hard Coded Credentials (CVE-2021-22707)
The authentication for the EVlink administration web interface can be bypassed
with undocumented and hard coded HTTP cookie values. Initial analysis indicates
that this authentication method is intended for local authentication by the
"evse" service.

2) Lack of Secure Update Mechanism / Remote Code Execution (CVE-2021-22708)
An authenticated attacker can upload arbitrary, malicious firmware updates to
the device and thus gain remote code execution. The firmware integrity is
checked by generating a SHA256 hash of the firmware update contents and a hard
coded value and comparing it against a hash stored within the firmware update
(CONTROL file).

An attacker can create a malicious firmware update by modifying the firmware
contents and adjusting the hash in the CONTROL file.

Based on public information we believe this vulnerability type was once
reported as CVE-2018-7801 by Positive Technologies before.
The patch notes [1] indicate that a signature was introduced in R6 software
v3.2.0-12 as a fix. It is likely this fix did not actually fix the
vulnerability.

[1]https://download.schneider-electric.com/files?p_enDocType=Software+-+Release+Notes&p_File_Name=Annotation_to_SEVD-2018-354-01_Security+Notification.pdf&p_Doc_Ref=annotation_SEVD-2018-354-01 <https://download.schneider-electric.com/files?p_enDocType=Software+-+Release+Notes&p_File_Name=Annotation_to_SEVD-2018-354-01_Security+Notification.pdf&p_Doc_Ref=annotation_SEVD-2018-354-01>


Proof of concept:
-----------------
1) Authentication Bypass with Undocumented Hard Coded Credentials (CVE-2021-22707)
The web interface authentication can be bypassed by setting the following HTTP
cookie values:
- CURLTOKEN=b35fcdc1ea1221e6dd126e172a0131c5a
- SESSIONID=admin

With those cookies the attacker is logged in with admin permissions.


2) Lack of Secure Update Mechanism / Remote Code Execution (CVE-2021-22708)
The file "epk-install.sh" stored in /mnt/datas/opt/evse/epk-install.sh performs
the validation of the firmware update image.

Below is an excerpt:
===========================================================
[...]
cd $INSTALL_DIR
[...]

# extract files from archive (epz is an epk.gz, but tar xf will handle it)
tar xf "$file"

if [[ ! -f CONTROL ]]; then
abort "KO, missing signature"
fi

echo $private_key > private

find . -type f | grep -v CONTROL | xargs sha256sum | awk '{print $1}' | sort | sha256sum > ../CONTROL2
mv ../CONTROL2 .
rm private

if [[ "`diff CONTROL CONTROL2`" != "" ]]; then
cat CONTROL CONTROL2
abort "KO, signatures mismatch"
fi
[...]
===========================================================

The $private_key parameter is not a cryptographic signature. It is a hard coded
key found in the "cgiServer" and "evse" binary and not a cryptographic
signature.
The value is: 67acdb2bce676ac1b1766c99b07f37fa591ea5f39f57afc874bab704a0a36964

It is placed in the firmware directory during the computation of the SHA256
hash.

This script can be modified easily to provide a valid hash for the CONTROL
file.


Vulnerable / tested versions:
-----------------------------
The vulnerabilities have been found in the firmware R7 (Version V3.3.0.15),
which is the latest version at the time of discovery.

Initial analysis indicates that at least the following Schneider Electric
products are affected:
- EVlink Charging Smart Wallbox
- EVlink Parking
- EVlink City ranges


Vendor contact timeline:
------------------------
2021-03-11 | Contacting vendor [email protected] <mailto:[email protected]>
2021-03-11 | Vendor response, vulnerabilities are under investigation.
2021-03-11 | Vendor response, vulnerabilities confirmed, fix and disclosure
scheduled for July 2021.
2021-07-14 | Coordinated release of security advisory.


Solution:
---------

Update to the most recent firmware version provided on the vendor's website.

Version R8 V3.4.0.1 includes a fix for the vulnerabilities.

Further information can be found in the Schneider Electric security
notification:
http://download.schneider-electric.com/files?p_Doc_Ref=SEVD-2021-194-06 <http://download.schneider-electric.com/files?p_Doc_Ref=SEVD-2021-194-06>

Workaround:
-----------
None


Advisory URL:
-------------
https://sec-consult.com/vulnerability-lab/ <https://sec-consult.com/vulnerability-lab/>

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

SEC Consult Vulnerability Lab

SEC Consult, an Atos company
Europe | Asia | North America

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and valid recommendation about the risk profile of new technologies.

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EOF Stefan Viehböck / @2021

 

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