Hard-coded key vulnerability in Logix PLCs has severity score of 10 out of 10

Hard-coded key vulnerability in Logix PLCs has severity score of 10 out of 10
Rockwell Automation

Hardware that is widely used to control equipment in factories and other industrial settings can be remotely commandeered by exploiting a newly disclosed vulnerability that has a severity score of 10 out of 10.

The vulnerability is found in programmable logic controllers from Rockwell Automation that are marketed under the Logix brand. These devices, which range from the size of a small toaster to a large bread box or even bigger, help control equipment and processes on assembly lines and in other manufacturing environments. Engineers program the PLCs using Rockwell software called Studio 5000 Logix Designer.

On Thursday, the US Cybersecurity & Infrastructure Security Administration warned of a critical vulnerability that could allow hackers to remotely connect to Logix controllers and from there alter their configuration or application code. The vulnerability requires a low skill level to be exploited, CISA said.

The vulnerability, which is tracked as CVE-2021-22681, is the result of the Studio 5000 Logix Designer software making it possible for hackers to extract a secret encryption key. This key is hard-coded into both Logix controllers and engineering stations and verifies communication between the two devices. A hacker who obtained the key could then mimic an engineering workstation and manipulate PLC code or configurations that directly impact a manufacturing process.

“Any affected Rockwell Logix controller that is exposed on the Internet is potentially vulnerable and exploitable,” said Sharon Brizinov, principal vulnerability researcher at Claroty, one of three organizations Rockwell credited with independently discovering the flaw. “To successfully exploit this vulnerability, an attacker must first obtain the secret key and have the knowledge of the cryptographic algorithm being used in the authentication process.”

Brizinov said that Claroty notified Rockwell of the vulnerability in 2019. Rockwell didn’t disclose it until Thursday. Rockwell also credited Kaspersky Lab and Soonchunhyang University researchers Eunseon Jeong, Youngho An, Junyoung Park, Insu Oh, and Kangbin Yim.

The vulnerability affects just about every Logix PLC Rockwell sells, including:

  • CompactLogix 1768
  • CompactLogix 1769
  • CompactLogix 5370
  • CompactLogix 5380
  • CompactLogix 5480
  • ControlLogix 5550
  • ControlLogix 5560
  • ControlLogix 5570
  • ControlLogix 5580
  • DriveLogix 5560
  • DriveLogix 5730
  • DriveLogix 1794-L34
  • Compact GuardLogix 5370
  • Compact GuardLogix 5380
  • GuardLogix 5570
  • GuardLogix 5580
  • SoftLogix 5800

Rockwell isn’t issuing a patch that directly addresses the problems stemming from the hard-coded key. Instead, the company is recommending that PLC users follow specific risk mitigation steps. The steps involve putting the controller mode switch into run, and if that’s not possible, following other recommendations that are specific to each PLC model.

Those steps are laid out in an advisory Rockwell is making available to customers, as well as in the above-linked CISA advisory. Rockwell and CISA also recommend PLC users follow standard security-in-depth security advice. Chief among the recommendations is ensuring that control system devices aren’t accessible from the Internet.

Security professionals universally admonish engineers to place critical industrial systems behind a firewall so they aren’t exposed to the Internet. Unfortunately, engineers struggling with high workloads and limited budgets often don’t heed the advice. The latest reminder of this came earlier this month when a municipal water treatment plant in Florida said that an intruder accessed a remote system and tried to lace drinking water with lye. Plant employees used the same TeamViewer password and didn’t put the system behind a firewall.

If Logix PLC users are segmenting industrial control networks and following other best practices, it’s likely that the risk posed by CVE-2021-22681 is minimal. And if people haven’t implemented these practices, hackers probably have easier ways to hijack the devices. That said, this vulnerability is serious enough that all Logix PLC users should pay attention to the CISA and Rockwell advisories.

Claroty has issued its own writeup here.

https://arstechnica.com/?p=1745776