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Claroty reveals DoS vulnerability in Siemens protocol

20 Feb 2020

Claroty has today announced its discovery of a vulnerability in the Siemens Digsi 4 protocol. 

The threat allows for a denial-of-service (DoS) attack against Siemens SIPROTEC 4 protection relays, designed specifically for electrical substations. 

The vulnerability was discovered by Claroty researcher Tal Keren.

The security breach represents the same protocol that was exploited by the Industroyer malware, also referred to as Crashoverride, which was used to attack a Ukrainian power grid in 2016.   

Claroty immediately reported this research and coordinated with Siemens, which has now released an advisory with workarounds and mitigations.

It contained targeted industrial cybersecurity (ICS) payloads that allowed it to communicate using ICS protocols and specifically attack the electrical substations of the targeted companies. 

An important component in a substation is the protection relay, which is responsible for monitoring the actual current transmitted in every location and may trip any circuit breaker if anything unexpected happens. 

Without this protection relay, anything from a power outage to physical damage and even safety issues could occur.

Some of the payloads used by Industroyer were designed to cause DoS on the protection relays and remote terminal units (RTU) used in the targeted power grid companies and act as a kill switch. 

One of the specifically targeted ICS payloads found in the Industroyer malware that was implemented caused DoS on Siemens SIPROTEC 4 protection relays. 

This vulnerability used the SIPROTEC 4 programming protocol (Digsi 4) that communicates over UDP port 50000, and the proof of concept (POC) code implementing it is available publicly.  

The newest vulnerability discovered by Claroty uses a malicious packet in that same protocol to cause a DoS on those relays, thus allowing an attacker to reproduce the damage caused by Industroyer. 

This Digsi4 protocol allows users to program the protection relay and change its behaviour.

This protocol was developed by Siemens as a proprietary protocol.

The challenge for traditional IT security products aiming to protect against such attacks is exacerbated, as a specific understanding of the protocol and deep packet inspection (DPI) capabilities are required. 

The advisory published by Siemens contains workarounds and mitigations for this issue. 

Siemens has also improved security in the newer SIPROTEC 5 relays, whose communication protocol is encrypted and utilises improved security. 

Many other protection relays and other types of ICS hardware in the industry use proprietary protocols for programming purposes.

Securing these critical devices requires a deep understanding of those protocols, a fundamental knowledge of Operational Technology (OT) security, and continuous research to find and map potential vulnerabilities—whether in the design of the protocol, implementation, or determining attempts to abuse it.