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/
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] download.schneider-electric.com/files
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
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