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Advisory ID: SYSS-2016-038
Product: CHERRY B.UNLIMITED AES
Manufacturer: Cherry GmbH
Affected Version(s): JD-0400EU-2/01
Tested Version(s): JD-0400EU-2/01
Vulnerability Type: Cryptographic Issues (CWE-310)
                    Keystroke Injection Vulnerability
Risk Level: High
Solution Status: Open
Manufacturer Notification: 2016-05-04
Solution Date: -
Public Disclosure: 2016-07-29
CVE Reference: Not yet assigned
Authors of Advisory: Matthias Deeg and Gerhard Klostermeier (SySS GmbH)

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Overview:

CHERRY B.UNLIMITED AES is a wireless desktop set consisting of a
mouse and a keyboard.

The manufacturer describes the product as follows (see [1]):

"CHERRY B. UNLIMITED AES combines secure data transmission and an
advanced energy supply in a design which has been thought through to the
very last detail. For high professional requirements and security both
at home and in the workplace."

Some of the key benefits of CHERRY B.UNLIMITED AES are (see [2]):

* Data transmission using 128-bit encryption, complying to Advanced 
  Encryption Standard (AES)
* USB cable charging function for both keyboard & mouse - even when in
  use
* High-quality, pre-charged NiMH batteries from GP with a very low
  self-discharge
* Almost interference-free wireless 2.4 GHz technology (range of up to
  10 metres)
* 3-button mouse: infrared sensor and adjustable resolution
  (1,000/2,000 dpi) with ergonomic side panels
* Multi-station capability operation of several wireless products in
  one room
* Easy to install, requiring no technical knowledge
* Mini USB receiver
* Keyboard awarded the "Blauer Engel" environmental seal

Due to an insecure implementation of the encrypted data communication,
the wireless keyboard CHERRY B.UNLIMITED AES is prone to keystroke
injection attacks.

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Vulnerability Details:

The SySS GmbH found out that the wireless keyboard CHERRY B.UNLIMITED 
AES is prone to keystroke injection attacks.  

An attacker can sniff the AES-encrypted data packets of the 2.4 GHz
radio communication sent by the keyboard to the receiver (USB dongle)
and identify key release data packets by means of time correlation.
For example, the last sent data packet before a longer time period
without any data communication usually is a key release packet.

The plaintext of such key release data packets and the AES encryption
using counter mode is known to an attacker by a previously performed
analysis of an attacker-owned device (see SySS security advisory
SYSS-2016-031).

Due to the insecure implementation of the AES-encrypted data
communication, an attacker can modify a previously sniffed encrypted
key release data packet and transmit it to the CHERRY B.UNLIMITED AES
USB dongle in order to inject arbitrary keystrokes of his choice.

Thus, despite AES-encrypted data communication, an attacker is able to
send arbitrary keystrokes to a victim's computer system. In this way, an
attacker can remotely take control over the victim's computer that is
operated with an affected CHERRY B.UNLIMITED AES wireless keyboard. 

In combination with the replay attack described in the SySS security
advisory SYSS-2016-031 (see [3]), a keystroke injection attack allows to
remotely attack computer systems with an active screen lock, for example
in order to install malware when the target system is unattended.

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Proof of Concept (PoC):

The SySS GmbH could successfully perform keystroke injection attacks
against the wireless keyboard CHERRY B.UNLIMITED AES using an in-house
developed software tool in combination with the USB radio dongle
Crazyradio PA (see [4]).

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Solution:

According to information from the manufacturer Cherry GmbH, the reported
security issue will currently not be fixed in affected products.

The written statement in German from Cherry GmbH regarding this and other
reported security issues is:

"Nach Prufung der von Ihnen festgestellten 'Sicherheitsschwachstellen'
haben wir uns dazu entschlossen, die AES Verschlusselung bis auf weiters
nicht weiter mit den Produkt zu promoten. Derzeit arbeiten wir an einem
Nachfolgeprodukt. Wie bisher, empfehlen wir Kunden mit hohen
Sicherheitsanfordungen ein kabelgebundenes Produkt zu verwenden.
Je nach Anforderung, auch mit CC-Zertifizierung."

The English translation of this statement is:

"We have examined the 'security flaws' you reported to us. As a result,
we decided, until further notice, to no longer refer to AES encryption
in order to promote the affected product. At the moment, we are
currently working on a successor product. As we already did in the past,
we recommend to our customers having particularly high security demands
using wired products which, depending on the requirements, should be 
CC certified."

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

Disclosure Timeline:

2016-05-04: Vulnerability reported to manufacturer
2016-05-24: Response from manufacturer with information about
            the reported security issue and rescheduling of the
            publication date in agreement with the manufacturer
2016-07-04: Received written statement from manufacturer concerning the
            reported security issue
2016-07-29: Public release of the security advisory

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

References:

[1] Data sheet for CHERRY B.UNLIMITED AES
    http://cherry.de/PDF/EN_CHERRY_B_UNLIMITED_AES.pdf
[2] Product website for CHERRY B.UNLIMITED AES
    http://cherry.de/cid/wireless_keyboards_CHERRY_B_UNLIMITED_AES.htm?rdeLocaleAttr=en&WT.mc_id=
[3] SySS Security Advisory SYSS-2016-031
    https://www.syss.de/fileadmin/dokumente/Publikationen/Advisories/SYSS-2016-031.txt
[4] Product website for Crazyradio PA
    https://www.bitcraze.io/crazyradio-pa/
[5] SySS Security Advisory SYSS-2016-038
    https://www.syss.de/fileadmin/dokumente/Publikationen/Advisories/SYSS-2016-038.txt
[6] SySS Responsible Disclosure Policy
    https://www.syss.de/en/responsible-disclosure-policy/

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

Credits:

This security vulnerability was found by Matthias Deeg and Gerhard
Klostermeier of the SySS GmbH.

E-Mail: matthias.deeg (at) syss.de
Public Key: https://www.syss.de/fileadmin/dokumente/Materialien/PGPKeys/Matthias_Deeg.asc
Key fingerprint = D1F0 A035 F06C E675 CDB9 0514 D9A4 BF6A 34AD 4DAB

E-Mail: gerhard.klostermeier (at) syss.de
Public Key: https://www.syss.de/fileadmin/dokumente/PGPKeys/Gerhard_Klostermeier.asc
Key fingerprint = 8A9E 75CC D510 4FF6 8DB5 CC30 3802 3AAB 573E B2E7

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

Disclaimer:

The information provided in this security advisory is provided "as is" 
and without warranty of any kind. Details of this security advisory may 
be updated in order to provide as accurate information as possible. The
latest version of this security advisory is available on the SySS Web 
site.

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

Copyright:

Creative Commons - Attribution (by) - Version 3.0
URL: http://creativecommons.org/licenses/by/3.0/deed.en

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