Security Experts:

PLCs From Several Vendors Vulnerable to Replay Attacks

Programmable logic controllers (PLCs) from several major vendors are affected by implementation flaws that can be exploited by attackers to execute arbitrary commands on the vulnerable devices, researchers warned.

The vulnerabilities, identified by ICS security firm CRITIFENCE, are related to the Modbus communications protocol, which is often used for connecting industrial devices. The company has been criticized for leading people to believe that ransomware attacks leveraging the flaws had already been spotted in the wild.

According to CRITIFENCE, devices from several companies are vulnerable to attacks, including Schneider Electric, GE and Rockwell Automation’s Allen-Bradley.

For the time being, only Schneider addressed the problem and the advisory published by the security firm focuses on Schneider products. ICS-CERT and other affected vendors have been notified.

In the case of Schneider, the vulnerabilities affect Modicon PLCs. The company has not released any firmware updates, but pointed out that some of its products already include protection mechanisms for these types of attacks, and provided mitigation advice for devices that don’t have any built-in protections.

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CRITIFENCE said in its advisory that attacks are possible against Schneider PLCs due to two vulnerabilities: CVE-2017-6034 and CVE-2017-6032. An attacker who has access to the OT network can intercept traffic going to the targeted PLC, including the session identifier needed to send administrative commands to the device.

Once they obtain the session key, which is transmitted in clear text, attackers can replay the request and add arbitrary commands, including for starting and stopping the PLC, and downloading its ladder diagram.

CRITIFENCE has published a proof-of-concept (PoC) exploit showing how a remote attacker can execute arbitrary commands on a Schneider PLC. The company believes these types of flaws can be exploited in ransomware-style attacks where hackers threaten to wipe ladder diagrams from PLCs unless their demands are met.

This attack scenario, dubbed “ClearEnergy” by CRITIFENCE, has drawn criticism from some ICS security experts. CRITIFENCE initially led to believe that ClearEnergy attacks were actually spotted in the wild with a news article named “ClearEnergy ransomware aim to destroy process automation logics in critical infrastructure, SCADA and industrial control systems.” The company later clarified that it was only a PoC ransomware attack.

Related: Researchers Disclose Unpatched Flaws in Schneider Electric PLCs

Related: Schneider Electric Patches Flaws in Modicon, Wonderware Products

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Eduard Kovacs is an international correspondent for SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.