"This attack can be used not only to control the PLC but also to turn the PLC into an 'agent' to attack other devices in the network," Ruben Santamarta, a security researcher from security firm IOActive, said Friday via email. Santamarta found vulnerabilities in industrial control systems in the past as part of Project Basecamp.
"We are aware of this security issue," Edwin Schwellinger, support manager at 3S-Smart Software, said Friday via email. "A patch is under development but not released. We are working with high pressure on these issues."
The vulnerability is only exploitable by an attacker who already has access to the network where the PLC runtime operates, Schwellinger said. Runtime systems should not be accessible from the Internet unless additional protection is in place, he said.
"Quite a few vulnerable CoDeSys systems are Internet-exposed," Reid Wightman, who now works as a security consultant for IOActive, said Thursday on Twitter. "Some found via shodan [a search engine], some found via custom scanning."
"No PLC should be accessible from the Internet ever," Santamarta said. However, many networks are compromised via advanced persistent threats -- malware that provides attackers with local network access -- and in those cases the perimeter doesn't matter anymore, he said.
"As much as possible avoid to expose PLCs and PLC networks to public networks and Internet," Schwellinger said. Customers should use additional security layers like virtual private networks (VPNs) for remote access, should install firewalls and should restrict access to sensitive networks only to authorized people, he said.
"Anything related to the SCADA [supervisory control and data acquisition] environment is a serious matter," said Luigi Auriemma, a security researcher at vulnerability research firm ReVuln who previously found and disclosed vulnerabilities in SCADA systems, via email Friday. "If you can control the PLC then you can control the infrastructure."
For example, after infecting PLCs at Iran's Natanz nuclear fuel enrichment plant, the Stuxnet malware altered their programming and destroyed around 1,000 uranium enrichment centrifuges. The attack is believed to have set back Iran's nuclear program by up to two years.
Fortunately, there are some workarounds that vendors can implement in the absence of an official patch.