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Fronius Solar Inverter Series Insecure Communication / Path Traversal

Fronius Solar Inverter Series Insecure Communication / Path Traversal
Posted Dec 4, 2019
Authored by T. Weber | Site sec-consult.com

Fronius Solar Inverter Series with software versions below 3.14.1 (HM 1.12.1) suffer from unencrypted communication and path traversal vulnerabilities.

tags | exploit, vulnerability
advisories | CVE-2019-19228, CVE-2019-19229
MD5 | 0caf8457f509b9b49092b83b93420e13

Fronius Solar Inverter Series Insecure Communication / Path Traversal

Change Mirror Download
SEC Consult Vulnerability Lab Security Advisory < 20191203-0 >
=======================================================================
title: Multiple vulnerabilites
product: Fronius Solar Inverter Series
vulnerable version: SW Version <3.14.1 (HM 1.12.1)
fixed version: >=3.14.1 (vuln 2: 3.12.5 - HM 1.10.5), see solution
section below
CVE number: CVE-2019-19228, CVE-2019-19229
impact: High
homepage: https://www.fronius.com
found: 2018-10-31
by: T. Weber (Office Vienna)
SEC Consult Vulnerability Lab

An integrated part of SEC Consult
Europe | Asia | North America

https://www.sec-consult.com

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

Vendor description:
-------------------
"A passion for new technologies, intensive research and revolutionary solutions
have been shaping the Fronius brand since 1945. As the technology leader, we
find, develop and implement innovative methods to monitor and control energy
for welding technology, photovoltaics and battery charging. We forge new paths,
try something difficult and succeed where others have failed in achieving what
seems to be impossible. [...]"

Source: http://www.fronius.com/en/about-fronius/company-values


Business recommendation:
------------------------
The vendor automatically performed a fleet update of the solar inverters in the field
in order to patch them. Nevertheless, as not all devices could be reached through such
an update, all remaining users are advised to install the patches provided
by the vendor immediately.


Vulnerability overview/description:
-----------------------------------
1) Unencrypted Communication
The whole communication is handled over HTTP. There is no possibility to
activate an HTTPS web service. This vulnerability cannot be fixed by the vendor
in the current solar inverter generation, see the workaround section below.


2) Authenticated Path Traversal (CVE-2019-19229)
A path traversal attack for authenticated users is possible. This allows getting
access to the operating system of the device and access information like
network configurations and connections to other hosts or potentially other
sensitive information.

This vulnerability has been fixed in March 2019 in version 3.12.5. (HM 1.10.5).

The web server runs with "nobody" privileges, but nearly all files on the
file system are world-readable and can be extracted. This can be seen as
another vulnerability but according to the vendor this cannot be fixed in the
current solar inverter generation.


3) Backdoor Account (CVE-2019-19228)
The web interface has a backdoor user account with the username "today".
This user account has all permissions of all other users ("service",
"admin" and "user") together.
As its name suggests, the password for the user "today" changes every day
and seems to be different to other devices with the same firmware. This
means that some device-specific strings (e.g. the public device-ID) is
mixed up every day to generate a new password.
This account is being used by Fronius support in order to access the
device upon request from the user.

The fix for this issue has been split in two parts. The "password reset"
part has been fixed in version 3.14.1 (HM 1.12.1) and the second part providing the
support account needs an architectural rework which will be fixed in a
future version (planned for 3.15.1 (HM 1.15.1)).

The passwords for all users of the web interface are stored in plain-text.
This can be seen as another vulnerability and it has been fixed in
version 3.14.1 (HM 1.12.1).


4) Outdated and Vulnerable Software Components
Outdated and vulnerable software components were found on the device during
a quick examination. Not all of the outdated components can be fixed by the vendor
in the current solar inverter generation, see the workaround section below.


Proof of concept:
-----------------
1) Unencrypted Communication
By using an interceptor proxy this vulnerability can be verified in a
simple way.


2) Authenticated Path Traversal (CVE-2019-19229)
By sending the following request to the following endpoint, a path traversal
vulnerability can be triggered:
http://<IP-Address>/admincgi-bin/service.fcgi

Request to read the "/etc/shadow" password file:
┌──────────────────────────────────────────────────────────────────────────────
|GET /admincgi-bin/service.fcgi?action=download&filename=../../../../../etc/shadow
└──────────────────────────────────────────────────────────────────────────────

As response, the file is returned without line breaks. In this example the
line breaks are added for better readability:

┌──────────────────────────────────────────────────────────────────────────────
|HTTP/1.1 200 OK
|Content-Type: application/force-download
|Content-Disposition: attachment; filename=../../../../../etc/shadow
|Connection: close
|Date: Sun, 28 Oct 2018 08:20:27 GMT
|Server: webserver
|
|root:$1$6MNb1Vq3$oU4TaPqQ782Y2ybdWLICh1:0:1:99999:7:::
|nobody:*:10897:0:99999:7:::
|messagebus:$1$6JrvtnWp$T.JvjxjbGTCD.jF7.hhb3.:15638:0:99999:7:::
└──────────────────────────────────────────────────────────────────────────────

By retrieving the file "/etc/issue" an easter-egg was found:
┌──────────────────────────────────────────────────────────────────────────────
| __ ___ _ _ _ _ __ ___ _ __ __ _
|\\ \\ / (_|_|_|_) |_ __ __ _ __ _ __ _ / / | \\| | \\ \\ / /___| |__
| \\ \\/\\/ /| | | | | | ' \\/ _` / _` / _` | / / | |) | |__ \\ \\/\\/ // -_) '_ \\
| \\_/ \\_/ |_|_|_|_|_|_|_|_\\__,_\\__,_\\__,_| /_/ |___/|____| \\_/ \\_/\\___|_.__/
|Congratulations to all non Fronius employees which have come so far :)
└──────────────────────────────────────────────────────────────────────────────

3) Backdoor Account (CVE-2019-19228)
The passwords of the web interface of the affected versions are stored in the file
"/tmp/web_users.conf" in clear text:
┌──────────────────────────────────────────────────────────────────────────────
|admin:<user-password>
|service:<user-password>
|today:<40-bit hash-value>
└──────────────────────────────────────────────────────────────────────────────

The password for "today", which is generated by some algorithm, is suspected
to be a sha1-hash which includes the system-time. A detailed firmware analysis
can reveal the algorithm but has not been performed for this advisory.


4) Outdated and Vulnerable Software Components
By using the path traversal vulnerability (2) a lot of components are found to
be outdated:

* Busybox 1.22.1 (December 23, 2014) multiple CVEs
* Lighttpd 1.4.33 (September 27, 2013) multiple CVEs
* Linux kernel 4.1.39 (March 13, 2017) multiple CVEs

The used SDK is based on the OSELAS toolchain from 2011 and U-Boot from 2012:
* gcc version 4.6.2 (OSELAS.Toolchain-2011.11.1)
* U-Boot 2012.07-3


Vulnerable / tested versions:
-----------------------------
The Fronius Symo 10.0-3-M (1) SWVersion 3.10.3-1 (HM 1.9.2) was tested but more solar
inverters from Fronius share this firmware. The following list has been provided by
the vendor:

Symo Hybrid 3.0-3-M
Symo Hybrid 4.0-3-M
Symo Hybrid 5.0-3-M
Datamanager Box 2.0
Symo 3.0-3-M *)
Symo 3.0-3-S *)
Symo 3.7-3-M *)
Symo 3.7-3-S *)
Symo 4.5-3-M *)
Symo 4.5-3-S *)
Symo 5.0-3-M *)
Symo 6.0-3-M *)
Symo 7.0-3-M *)
Symo 8.2-3-M *)
Symo 10.0-3-M *) (tested)
Symo 10.0-3-M-OS *)
Symo 12.5-3-M *)
Symo 15.0-3-M *)
Symo 17.5-3-M *)
Symo 20.0-3-M *)
Galvo 1.5-1 *)
Galvo 2.0-1 *)
Galvo 2.5-1 *)
Galvo 3.0-1 *)
Galvo 3.1-1 *)
Galvo 1.5-1 208-240 *)
Galvo 2.0-1 208-240 *)
Galvo 2.5-1 208-240 *)
Galvo 3.1-1 208-240 *)
Primo 3.0-1 *)
Primo 3.5-1 *)
Primo 3.6-1 *)
Primo 4.0-1 *)
Primo 4.6-1 *)
Primo 5.0-1 *)
Primo 5.0-1 AUS *)
Primo 5.0-1 SC *)
Primo 6.0-1 *)
Primo 8.2-1 *)
Primo 3.8-1 208-240 *)
Primo 5.0-1 208-240 *)
Primo 6.0-1 208-240 *)
Primo 7.6-1 208-240 *)
Primo 8.2-1 208-240 *)
Primo 10.0-1 208-240 *)
Primo 11.4-1 208-240 *)
Primo 12.5-1 208-240 *)
Primo 15.0-1 208-240 *)
Symo 10.0-3 208-240 *)
Symo 10.0-3 480 *)
Symo 12.0-3 208-240 *)
Symo 12.5-3 480 *)
Symo 15.0-3 107 *)
Symo 15.0-3 480 *)
Symo 17.5-3 480 *)
Symo 20.0-3 480 *)
Symo 22.7-3 480 *)
Symo 24.0-3 480 *)
Eco 25.0-3-S *)
Eco 27.0-3-S *)
Symo Advanced 10.0-3 208-240 *)
Symo Advanced 12.0-3 208-240 *)
Symo Advanced 15.0-3 480 *)
Symo Advanced 20.0-3 480 *)
Symo Advanced 22.7-3 480 *)
Symo Advanced 24.0-3 480 *)
*) only with Datamanager card/box


Vendor contact timeline:
------------------------
2018-11-05: Contacting vendor through contact@fronius.com, requesting
security contact
2018-11-06: Vendor replies and confirms security issues
2018-12-03: Meeting with vendor to discuss security issues
2019-01 - 2019-11: Multiple telcos discussing Fronius' rollout plan and fixes
2019-03-18: Release of version 3.12.5 (HM 1.10.5) which fixes the path traversal vulnerability
2019-07-30: Release of version 3.14.1 (HM 1.12.1) which fixes many of the other reported issues
2019-08 - 2019-11: Testing & Fleet update to version 3.14.1 (HM 1.12.1)
2019-12-03: Coordinated release of security advisory


Solution:
---------
The vendor provides a patched firmware via their download portal. Visit
the download page and search for "firmware update" and choose the
"Fronius Solar.update Datamanager V3.14.1-10" firmware.

The new version v3.14.1 (HM 1.12.1) which contains most of the security fixes can be
downloaded directly as well:
https://www.fronius.com/~/downloads/Solar%20Energy/Firmware/SE_FW_Fronius_Solar.update_Datamanager_EN.zip

Some of the identified vulnerabilities (e.g. issue 1 and parts of 4) cannot be fixed
in the current solar inverter product/software generation. Issue 2 (path traversal)
has been fixed in version 3.12.5 (HM 1.10.5).


Workaround:
-----------
Restrict network access to the device as much as possible and disable port forwarding
from the Internet. Fronius Solar.Web access is still possible.


Advisory URL:
-------------
https://www.sec-consult.com/en/vulnerability-lab/advisories/index.html


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

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SEC Consult
Europe | Asia | North America

About SEC Consult Vulnerability Lab
The SEC Consult Vulnerability Lab is an integrated part of SEC Consult. It
ensures the continued knowledge gain of SEC Consult in the field of network
and application security to stay ahead of the attacker. The SEC Consult
Vulnerability Lab supports high-quality penetration testing and the evaluation
of new offensive and defensive technologies for our customers. Hence our
customers obtain the most current information about vulnerabilities and valid
recommendation about the risk profile of new technologies.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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EOF T. Weber / @2019

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