A critical authentication bypass vulnerability could be exploited by remote attackers to Rockwell Automation programmable logic controllers (PLCs).

A critical authentication bypass vulnerability, tracked as CVE-2021-22681, can be exploited by remote attackers to compromise programmable logic controllers (PLCs) manufactured by Rockwell Automation.

The vulnerability was independently reported to Rockwell by researchers at the Soonchunhyang University in South Korea, Claroty, and Kaspersky.

“Successful exploitation of this vulnerability could allow a remote unauthenticated attacker to bypass the verification mechanism and connect with Logix controllers.” reads the advisory published by CISA. “Additionally, this vulnerability could enable an unauthorized third-party tool to alter the controller’s configuration and/or application code.”

The CVE-2021-22681 flaw has received a CVSS score of 10, it affects the following products:

Rockwell software versions:

RSLogix 5000: Versions 16 through 20Studio 5000 Logix Designer: Versions 21 and laterRockwell Logix Controllers:

CompactLogix 1768CompactLogix 1769CompactLogix 5370CompactLogix 5380CompactLogix 5480ControlLogix 5550ControlLogix 5560ControlLogix 5570ControlLogix 5580DriveLogix 5560DriveLogix 5730DriveLogix 1794-L34Compact GuardLogix 5370Compact GuardLogix 5380GuardLogix 5570GuardLogix 5580SoftLogix 5800The issue resides in the Logix Designer software that uses a poorly protected private cryptographic key to verify communications with controllers.

“This key is not sufficiently protected, allowing a remote, unauthenticated attacker to bypass the verification mechanism and connect to the controller by mimicking an engineering workstation.” reads the post published by Claroty. “An attacker who is able to extract the secret key would be able to authenticate to any Rockwell Logix controller.”

The secret keys are used to digitally sign all communication with the Rockwell PLCs, then PLCs verify the signature and authenticate the company engineering software. An attacker that obtained the key impersonate the engineering software and control the PLC.

Claroty privately reported the vulnerability to Rockwell in 2019.

Rockwell provided a list of risk mitigation and recommended user actions for its projects.

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Pierluigi Paganini

(SecurityAffairs – hacking, PLC)

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