Several product lines from Siemens are affected by a serious vulnerability that can be exploited by a remote attacker to cause systems to enter a denial-of-service (DoS) condition.

The flaw, tracked as CVE-2017-12741 and rated “high severity,” was reported to Siemens by George Lashenko of industrial cybersecurity firm CyberX.

According to Siemens, the list of affected products includes SIMATIC S7-200 Smart micro-PLCs for small automation applications, some SIMATIC S7 CPUs, SIMATIC WinAC RTX software controllers, SIMATIC ET 200 PROFINET interface modules, SIMATIC PN/PN couplers, SIMATIC Compact field units, development kits for PROFINET IO, SIMOTION motion control systems, SINAMICS converters, SINUMERIK CNC automation solutions, SIMOCODE motor management systems, and SIRIUS 3RW motor soft starters.

An attacker can cause affected systems to malfunction by sending them specially crafted packets via UDP port 161, which is used for the simple network management protocol (SNMP). In order to recover from the DoS condition, the devices must be manually restarted.

The mitigating factors section of Siemens’ advisory lists the requirement that the attacker must have network access for exploitation, and the fact that it advises organizations to operate these devices only in trusted environments.

However, CyberX told SecurityWeek that there are roughly 2,000 Siemens devices accessible from the Internet, including approximately 400 that have an open SNMP port, which could make them vulnerable to the company’s exploit.

“DoS vulnerabilities shouldn’t be taken lightly,” CyberX said. “The December 2016 attack on the Ukrainian electrical grid used this type of exploit to disable protection relays and make it more difficult for operators to recover.”

The security firm said Siemens was very responsive to its vulnerability report. The vendor has released firmware updates that patch the flaw in some SIMATIC S7, EK-ERTEC, SIMOTION and SINAMICS products.

Until fixes become available for the other affected products, Siemens recommends disabling SNMP, which fully mitigates the vulnerability, protecting network access to port 161, applying defense-in-depth and cell protection concepts, and using VPNs.

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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.

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