Siemens fixes SCADA holes found by hacker

Vulns were kept quiet at request of manufacturer

Siemens has patched security vulnerabilities in its widely used Simatic S7 industrial computer system that made it possible for attackers to disrupt or sabotage operations at gas refineries, chemical plants and other critical facilities.

In an advisory (PDF) issued on Friday, the Industrial Control Systems Cyber Emergency Response Team said the Siemens update fixed a “portion” of the vulnerabilities discovered in the S7-1200 PLC, or programmable logic controller, by NSS Labs researcher Dillon Beresford. Last month, he and a colleague cancelled a scheduled talk about critical vulnerabilities in the PLC following requests by the German manufacturer and officials from the US Department of Homeland Security.

A separate advisory issued by Siemens said the updated firmware fixed two vulnerabilities.

The first enabled so-called replay attacks, in which digital communications between engineering software and the controller is recorded and then transmitted again at a later time. By capturing the data, attackers could use it later to carry out sensitive functions not specifically authorized. A mitigating caveat: the replayed data could be used only against the same controller that received the initial instructions. What's more, the attack would work only when an attacker had network access to the targeted PLC.

A second vulnerability allowed attackers to shut down a controller by overloading the communications it receives.

“The latest firmware update for the S7-1200 will offer corrective action for enhancing protection against replay attacks as well as increased stability when facing the above-mentioned denial-of-service scenario,” the Siemens advisory stated.

Beresford has stressed that he voluntarily canceled his talk but went on to blast Siemens engineers for downplaying the severity of his findings. He is scheduled to speak about the security of the PLCs in August during a briefing at the Black Hat security conference in Las Vegas. ®

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