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The State of XIoT Security Report: 1H 2022
An analysis of published cyber-physical systems vulnerabilities.
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Team82 Research


THE RACE TO NATIVE CODE EXECUTION IN PLCS: USING RCE TO UNCOVER SIEMENS SIMATIC
S7-1200/1500 HARDCODED CRYPTOGRAPHIC KEYS

Team82
/ October 11th, 2022



EXECUTIVE SUMMARY

 * Team82 has developed a new, innovative method to extract heavily guarded,
   hardcoded, global private cryptographic keys embedded within the Siemens
   SIMATIC S7-1200/1500 PLC and TIA Portal product lines.

 * An attacker can use these keys to perform multiple advanced attacks against
   Siemens SIMATIC devices and the related TIA Portal, while bypassing all four
   of its access level protections. 

 * A malicious actor could use this secret information to compromise the entire
   SIMATIC S7-1200/1500 product line in an irreparable way. 

 * All technical information was disclosed to Siemens, which released new
   versions of the affected PLCs and engineering workstation that address this
   vulnerability.

 * CVE-2022-38465 has been assigned, and a CVSS v3 score of 9.3 was assessed. 

 * In addition, an attacker can develop an independent Siemens SIMATIC client
   (without requiring the TIA Portal) and perform full upload/download
   procedures, conduct man-in-the-middle attacks, and intercept and decrypt
   passive OMS+ network traffic.

 * This work is an extension of our previous research into Siemens SIMATIC
   PLCs. 

 * Siemens has updated both the S7-1200 and S7-1500 PLCs and the TIA Portal, and
   urges users to move to current versions. 

 * This disclosure has led to the introduction of a new TLS management system in
   TIA Portal v17, ensuring that configuration data and communications between
   Siemens PLCs and engineering workstations is encrypted and confidential.

 * Siemens’ advisory can be found here. Siemens has also published a bulletin
   with remarks regarding its key protection update. Read it here.
   


INTRODUCTION 

Close to 10 years ago, Siemens introduced asymmetric cryptography into the
integrated security architecture of its TIA Portal v12 and SIMATIC S7-1200/1500
PLC CPU firmware families. This was done to ensure the integrity and
confidentiality of devices and user programs, as well as for the protection of
device communication within industrial environments. 



Dynamic key management and distribution did not exist then for industrial
control systems, largely because of the operational burden that key management
systems would put on integrators and users. Siemens decided at the time instead
to rely on fixed cryptographic keys to secure programming and communications
between its PLCs and the TIA portal. 


Since then, however, advances in technology, security research, and a swiftly
changing threat landscape have rendered such hardcoded crypto keys an
unacceptable risk. A malicious actor who is able to extract a global, hardcoded
key, could compromise the entire device product line security in an irreparable
way.


Team82 has to date conducted extensive research into PLC security, working
closely with leading vendors to eradicate such practices as hardcoded keys,
demonstrate the risk they pose to users’ systems, and improve the overall
security of the industrial automation ecosystem. 



Our latest work—an extension of previous research conducted on Siemens SIMATIC
S7-1200 and S7-1500 PLCs, as well as Rockwell Automation’s Logix controllers and
Studio 5000 Logix Designer—continues on that path. 



We uncovered and disclosed to Siemens a new and innovative technique targeting
SIMATIC S7-1200 and S7-1500 PLC CPUs that enabled our researchers to recover a
global hardcoded cryptographic key (CVE-2022-38465) used by each Siemens
affected product line. The key, if extracted by an attacker, would give them
full control over every PLC per affected Siemens product line. 



Using a vulnerability uncovered in previous research (CVE-2020-15782) on Siemens
PLCs that enabled us to bypass native memory protections on the PLC and gain
read and write privileges in order to remotely execute code, we were able to
extract the internal, heavily guarded private key used across the Siemens
product lines. This new knowledge allowed us to implement the full protocol
stack, encrypt and decrypt protected communication, and configurations.



Siemens’ response to this private disclosure led to an overhaul of the
cryptographic schemes protecting its flagship PLC lines, as well as its TIA
Portal engineering workstation application. Siemens acknowledged in a security
advisory that existing protections around its hardcoded key are no longer
sufficient, and invested the resources and time necessary to introduce a dynamic
public-key infrastructure (PKI) that eliminates the use of hardcoded keys. 


Siemens recommends users immediately update SIMATIC S7-1200 and S7-1500 PLCs and
corresponding versions of the TIA Portal project to the latest versions. TIA
Portal V17 and related CPU firmware versions include the new PKI system
protecting confidential configuration data based on individual passwords per
device and TLS-protected PG/PC and HMI communication, Siemens said in its
advisory.


TECHNICAL DETAILS 


SIEMENS ACCESS RESTRICTION MECHANISMS



A prominent security feature of Siemens PLCs is an access level restriction
mechanism that is enforced with password protection. A password is configured
within the project that is downloaded to the PLC along with a desired protection
level. Those levels are: 



 * Level 1: Full read and write access to any configuration and logic block

 * Level 2: Write protection: 
   
   * Can read everything
   
   * Can change PLC modes

 * Level 3: Limited read access:
   
   * Can read HMI data (values etc.)
   
   * Can read diagnostic data

 * Level 4: Full protection
   
   * Cannot communicate with the PLC without password






Siemens S7 1200/1500 Access Levels (Source: Siemens)

All four levels use the same security mechanism to grant permissions to the
user. The only difference between them is the extent of permissions granted with
or without authentication. A password is requested upon any connection to the
PLC.




UNDERSTANDING S7-1200, S7-1500 ENCRYPTION


The asymmetric encryption procedures on the Siemens flagship PLCs has two
principal purposes: 


 * Authentication: a shared derived session key that authenticates a user when
   communicating with a PLC.

 * Confidentiality: encrypting data during portions of said communication, i.e.,
   downloaded logic. 



We were able to understand the encryption algorithm, which was based on Elliptic
Curve asymmetric encryption. We found the curve parameters as well as an added
complication: the use of a “configuration key” to further obfuscate and
complicate the elliptical multiplication process. 



Eventually we were able to uncover all the relevant keys involved in the
encryption process:


 * Connection Key: Used for packet integrity verification and authentication.

 * CPU Key: A “per-model/firmware” (e.g S7-1518, S7-1517) key used to encrypt
   configurations, code, and maintain code integrity.

 * Family Key: A “per-family” (e.g S7-1200, S7-1500) used for the same purposes
   as the CPU key, when the CPU key is not known.

An illustration of the keys used in Siemens PLC encryption process.






GAINING CODE EXECUTION ON THE PLC

After reverse engineering one of Siemens SIMATIC .upd firmware S7-1200 which
were unencrypted, we learned that the private key does not reside within the
firmware files, therefore we would have to extract it somehow directly from the
PLC. 



In order to retrieve the private key from the PLC, we needed direct memory
access (DA) to be able to search for it. To be able to perform DA actions, we
searched and found a remote code execution vulnerability on both the 1200/1500
PLC series. The vulnerability (CVE-2020-15782) was triggered through a specific
MC7+ function code containing our own crafted shellcode bytecode.

Our CVE-2020-15782 sandbox escape exploit.

The vulnerability logic for CVE-2020-15782 works as follows:

 * Use [REDACTED] opcode, which has no security memory region checks, to copy an
   internal struct containing a native pointer to a valid memory area to a
   writable memory area

 * Change the pointer inside this struct to our desired address

 * Recalculate the CRC that was used to verify this struct (using the CRC32
   opcode)

 * Copy the struct back to its original location, now pointing to our desired
   address, using the [REDACTED] opcode

 * At this point, we may use indirect access to the new address in our crafted
   struct.

MC7+ [REDACTED] opcode implementation function; since it missed the security
memory memory region check it was possible to exploit it and achieve RCE
(CVE-2020-15782).

We could now read or write from any memory address in the PLC. Using this
capability, we could override native code and execute any desired native logic.


We gave a detailed technical presentation about this vulnerability at the S4x22
Conference, below: 




USING THE RCE TO OBTAIN THE HIDDEN PRIVATE KEY



Using the DA read permission we obtained, we were able to extract the entire
encrypted PLC firmware (SIMATIC S7-1500) and map its functions. During the
mapping process we found a function that read the private key on the PLC.

The PoC we used to dump SIMATIC S7-1500 firmware from memory.

Once we had the function address, we rewrote the functionality of specific MC7+
opcodes with our shell code, forcing them to call the native function that reads
the private key. We then copied the key to a known memory address and read it
from there. Executing the overwritten function gave us the full private key of
the PLC. 


We later discovered that these keys are shared across each Siemens SIMATIC S7
product line, and immediately started a coordinated disclosure process with
Siemens. This resulted in a new advisory and CVE-2022-38465.



Using the same methodology, we were able to extract the configuration key from
the CPU.



Combining the private key, with the configuration key, and knowledge of the
algorithm, allowed us to implement the full protocol stack, encrypt/decrypt
protected communication, and configurations.

Demonstrating the vulnerability chain used to extract the private, global key.


ATTACK FLOWS: GAINING CONTROL OVER A PLC AND PROCESS

Using the private key we were able to extract, an attacker may gain full control
over a PLC.


ATTACKS ON THE PASSWORD 

The attacks described below allow an attacker with knowledge of the PLC’s
private key and encryption algorithm, to retrieve the configured password on the
PLC, thus gaining full control regardless of the protection level configured on
the device.


 * Obtain the Configuration and decrypt the password hash (reading
   configurations from the PLC): If the PLC is in a protection level lower than
   3, An attacker can retrieve the configuration from the PLC (Upload procedure)
   with no special permission required. Once uploaded, the attacker has the PLC
   configuration and can use the private key to decrypt the password hash from
   the uploaded configuration. Using the decrypted password hash the attacker
   can authenticate to the PLC and gain higher privileges.

 * Man in the Middle: An attacker with knowledge of the encryption mechanism of
   the traffic, as well as access to the private key, can impersonate the PLC in
   a connection.  The man in the middle attack is performed in the following
   steps:
   
   * The client (victim) connects to the attacker’s phony PLC and sends an
     encrypted connection key.
   
   * The attacker decrypts the connection key and uses the decrypted key to
     connect to the real PLC. Once connected, the attacker receives a
     password-based challenge.
   
   * The attacker forwards the real PLC’s challenge to the client and receives a
     valid challenge response.
   
   * The attacker then forwards the challenge response to the real PLC to set up
     an authenticated connection. This session will be a fully privileged
     session. At this point, the attacker may change any configuration or blocks
     on the PLC, or read the configuration. This access includes the ability to
     read the encrypted password hash from the PLC and decrypt it.

 * Passive Traffic Interception: An attacker with passive access to capture
   traffic to a given PLC on the network can intercept configuration
   reads/writes from the PLC. Using the private key, the attacker can decrypt
   the configuration and extract the password hash. With the password hash the
   attacker can authenticate to the controller and write a new configuration.




SUMMARY 

This attack (CVE-2022-38465) was made possible due to the ability to execute
native code on S7 PLCs we achieved with our previous research CVE-2020-15782.
Using native code execution, we were able to read the raw memory region
protecting the private key and eventually fully recover the key.



By extracting the PLC’s hardcoded private key, we were able to demonstrate
multiple attack scenarios including decryption of all communication between S7
PLCs and an EWS, decryption of the configured password hash on the PLC, which we
could use to gain full access to the PLC, conduct man-in-the-middle attacks, and
more.



Users should update to current versions of the S7-1200 and S7-1500 PLC families,
as well as TIA Portal v17, as advised by Siemens. TIA Portal v17 introduces a
TLS management system in order to encrypt communication. Siemens also introduced
a preactivated PLC configuration password requirement, that ensures all
confidential PLC configuration data are protected by default as well as
predefined secure PG/HMI communication, which prevents unsecured communication
with other partners, and preactivated PLC access protection, that prevents any
type of access to the controller unless explicitly configured.




THE VULNERABILITY 



CVE-2022-38465

CWE-522 Insufficiently Protected Credentials

CVSS v3 score: 9.3



Description: SIMATIC S7-1200, S7-1500 CPUs and related products protect the
built-in global private key in a way that cannot be considered sufficient any
longer. The key is used for the legacy protection of confidential configuration
data and the legacy PG/PC and HMI communication. This could allow attackers to
discover the private key of a CPU product family by an offline attack against a
single CPU of the family. Attackers could then use this knowledge to extract
confidential configuration data from projects that are protected by that key or
to perform attacks against legacy PG/PC and HMI communication.


ACKNOWLEDGMENT



Team82 would like to thank Siemens for its coordination in working through this
disclosure, and for its swift response in confirming our findings and patching
these vulnerabilities.




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RECENT VULNERABILITY DISCLOSURES

 * CVE-2022-38465
 * CVE-2022-41666
 * CVE-2022-41667
 * CVE-2022-41669
 * CVE-2022-41670

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