Exploit the possiblities

WAGO PFC 200 Series Authentication Bypass

WAGO PFC 200 Series Authentication Bypass
Posted Dec 4, 2017
Authored by T. Weber | Site sec-consult.com

WAGO PFC 200 Series suffers from multiple unauthenticated access bypass vulnerabilities.

tags | exploit, vulnerability
MD5 | e2abe1666aac18721e912c338c5dd1a2

WAGO PFC 200 Series Authentication Bypass

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SEC Consult Vulnerability Lab Security Advisory < 20171130-0 >
=======================================================================
title: Critical CODESYS vulnerabilities
product: WAGO PFC 200 Series, see "Vulnerable / tested versions"
vulnerable version: plclinux_rt 2.4.7.0, see "Vulnerable / tested versions"
fixed version: PFC200 FW11
CVE number: -
impact: critical
homepage: https://www.codesys.com
found: 2017-07-28
by: T. Weber (Office Vienna)
SEC Consult Vulnerability Lab

An integrated part of SEC Consult
Bangkok - Berlin - Linz - Luxembourg - Montreal - Moscow
Kuala Lumpur - Singapore - Vienna (HQ) - Vilnius - Zurich

https://www.sec-consult.com

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

Vendor description:
-------------------
"The WAGO-I/O-SYSTEM is a flexible fieldbus-independent solution for
decentralized automation tasks. With the relay, function and interface
modules, as well as overvoltage protection, WAGO provides a suitable interface
for any application."

Source: http://global.wago.com/en/products/product-catalog/
components-automation/overview/index.jsp

"The PFC family of controllers offers advanced compact, computing power for PLC
programming and process visualization. Programmable in accordance with IEC 61131-3
600, PFC controllers feature a 600 MHz ARM Cortex A8 processor that offers high
speed processing and support of 64 bit variables."

Source:
http://www.wago.us/products/components-for-automation/modular-io-system-series-750-753/programmable-fieldbus-controller/pfc200/index.jsp



Business recommendation:
------------------------
Because of the use in industrial and safety-critical environments the patch has
to be applied as soon as it is available. We explicitly point out to all users
in this sector that this device series in the mentioned device series with
firmware 02.07.07(10) should not be connected directly to the internet (or even
act as gateway) since it is very likely that an attacker can compromise the
whole network via such an device.

SEC Consult recommends not to use this product in a production environment
until a thorough security review has been performed by security professionals.


Vulnerability overview/description:
-----------------------------------
The "plclinux_rt" service accepts different unauthenticated actions.

This vulnerability contains the architectural security problems described by
Reid Wightman. The SDK of "plclinux_rt" is written by the same vendor (3S).
Therefore, the file commands of "Digital Bond's 3S CODESYS Tools", created
around 2012 are applicable.
(See https://ics-cert.us-cert.gov/advisories/ICSA-13-011-01)

The CODESYS command-line is protected with login credentials, that's why the
shell of the mentioned tools does not provide root access out of the box. But
after some investigation it was clear that there are further functions which
are reachable without using the command-line and without any authentication.

These functions in "plclinux_rt" can be triggered by sending the correct
TCP payload on the bound port (by default 2455).

Some of the triggerable functions are:
* Arbitrary file read/write/delete (also covered by "Digital Bond's Tools")
* Step over a function in the currently executed PLC program
* Cycle step any function in the currently executed PLC program
* Delete the current variable list of the currently executed PLC program
* And more functions...

Since SSH is activated by default, an unauthenticated attacker can rewrite
"/etc/shadow" and gain root privileges easily via these attack vectors!


1) Critical Improper Authentication / Design Issue
Files can be fetched, written and deleted. Running tasks on the PLC can be
restarted, stepped and crashed.

An attacker can therefore replace the password hash in the shadow file. A
memory corruption (and potential reverse-shell) is also possible via arbitrary
TCP packets.

There are potentially more commands which can be triggered, but this was not
covered by the short security crash test.


Proof of concept:
-----------------
As there is no patch available yet, the detailed proof of concept information has
been removed from this advisory.

1) Critical Improper Authentication / Design Issue
Two payloads are specified here as proof of concept for file manipulation.
Four payloads for live program manipulation are also listed.

File read and delete without any authentication.

Read "/etc/shadow":
echo '[PoC removed]' | xxd -r -p | nc <PLC-IP> <Port>

Delete "/etc/test":
echo '[PoC removed]' | xxd -r -p | nc <PLC-IP> <Port>

Runnning PLC tasks could be modified with the following payloads:

Step over function:
echo '[PoC removed]' | xxd -r -p | nc <PLC-IP> <Port>

Cycle step function:
echo '[PoC removed]' | xxd -r -p | nc <PLC-IP> <Port>

Delete variable list (produces stack-trace / denial of service):
echo '[PoC removed]' | xxd -r -p | nc <PLC-IP> <Port>

The actual function is chosen by the 7th byte in the latter payloads. E.g.:
0x31 -> read file
0x36 -> delete file
0x0a -> step over
0x24 -> cycle step
0x15 -> delete variable list

There are much more functions hidden in the "plclinux_rt" binary. This
is just an excerpt of a few available functions.

These functions can be examined from "SrvComputeService". Two pseudo code
snippets generated by IDA Pro shows some examples (the functionality can be
quickly determined from the corresponding debug message):
[PoC removed from this advisory]


Vulnerable / tested versions:
-----------------------------
WAGO PFC200 Series / Firmware 02.07.07(10)
(17 affected devices)
750-8202
750-8202/025-000
750-8202/025-001
750-8202/025-002
750-8202/040-001
750-8203
750-8203/025-000
750-8204
750-8204/025-000
750-8206
750-8206/025-000
750-8206/025-001
750-8207
750-8207/025-000
750-8207/025-001
750-8208
750-8208/025-000

The WAGO contact stated during a call that all PLCs of the 750-88X Series are not
vulnerable due to a custom fix from WAGO. The contact also stated that the PLCs
of the 750-810X (PFC100) series are also not vulnerable because they have
CODESYS 3.5 deployed.

Devices of any other vendor which use the CODESYS 2.3.X/2.4.X runtime are
potentially prone to the same vulnerability.


Vendor contact timeline:
------------------------
2017-08-02: Contacting vendor through info@wago.com and set the
publication date to 2017-09-21.
2017-08-09: Sending a reminder to info@wago.com
2017-08-16: Found a dedicated security contact of WAGO. Contacting
this employee via e-mail.
2017-08-17: Contact responds that he will read the redirected e-mail
from info@wago.com. Sending e-mail to contact that the
message sent to info@wago.com does not contain the actual
advisory and that an encrypted channel should be used for
transmission.
2017-08-22: Sending reminder to contact and re-transmitting the
responsible disclosure policy and all possible ways
to transmit the advisory.
2017-08-29: Uploading advisory to WAGO ShareFile.
2017-09-15: Telephone call with WAGO contact. Discussion about the
vulnerability. Fix will be available in the next firmware
version. Vendor clarified that series 750-88X is not prone
to the reported vulnerability. Set the publication date to
2017-09-28.
2017-09-26: Telephone call with vendor. Vendor is working on a fix of
the vulnerabilities. Set the publication date to 2017-10-12.
2017-10-06: Sending a reminder to the vendor; No answer.
2017-10-11: Sending a reminder to the vendor. Vendor states that they
are working on an update and a timeline for the fix will
be provided on 2017-10-13.
2017-10-13: Asked for an update; No answer.
2017-10-17: Informing the vendor that the publication date was set to
2017-10-23.
2017-10-19: Vendor responds that vulnerability in PFC200 series will be
patched in firmware version FW12. Set publication date to
2017-10-27 and asked the vendor for a time-line regarding
the PFC100 series.
2017-10-20: Vendor responds that PFC100 series is not vulnerable since
it does not contain CODESYS 2.4 run-time. Vendor corrected
the firmware to version FW11. The patch will be available
in January 2018.
2017-10-30: Informed vendor that the advisory will be published on
2017-11-30.
2017-11-30: Advisory release


Solution:
---------
Update your WAGO PFC200 Series to firmware version FW11 as soon as it is
available. In the meantime, see the workaround section.


Workaround:
-----------
Delete "plclinux_rt" or close the programming port (2455).
Network access to the device should be restricted.


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


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

SEC Consult Vulnerability Lab

SEC Consult
Bangkok - Berlin - Linz - Luxembourg - Montreal - Moscow
Kuala Lumpur - Singapore - Vienna (HQ) - Vilnius - Zurich

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.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Interested to work with the experts of SEC Consult?
Send us your application https://www.sec-consult.com/en/career/index.html

Interested in improving your cyber security with the experts of SEC Consult?
Contact our local offices https://www.sec-consult.com/en/contact/index.html
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Mail: research at sec-consult dot com
Web: https://www.sec-consult.com
Blog: http://blog.sec-consult.com
Twitter: https://twitter.com/sec_consult

EOF T. Weber / @2017


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