ICS Advisory (ICSA-11-279-04)

Beckhoff TwinCAT Read Access Violation

Click to Tweet.
Click to send to Facebook.
Click to Share.

Legal Notice

All information products included in https://us-cert.cisa.gov/ics are provided "as is" for informational purposes only. The Department of Homeland Security (DHS) does not provide any warranties of any kind regarding any information contained within. DHS does not endorse any commercial product or service, referenced in this product or otherwise. Further dissemination of this product is governed by the Traffic Light Protocol (TLP) marking in the header. For more information about TLP, see https://us-cert.cisa.gov/tlp/.



This Advisory is a follow-up to the Alert, ICS-ALERT-11-256-06—BECKHOFF TWINCAT READ ACCESS VIOLATION, that was published September 13, 2011, on the Industrial Control Systems Cyber Emergency Response Team (ICS-CERT) web page.

ICS-CERT is aware of a public report of a read access violation vulnerability in Beckhoff’s TwinCAT Software that could lead to a denial-of-service condition. Beckhoff has produced a patch to address this vulnerability in TwinCAT Software.

Affected Products

According to Beckhoff, the following product is affected:

  • TwinCAT versions 2.10, 2.11, 2.11R2


Successful exploitation of this vulnerability could result in a denial-of-service.

Impact to individual organizations depends on many factors that are unique to each organization. ICS-CERT recommends that organizations evaluate the impact of this vulnerability based on their environment, architecture, and product implementation.


Beckhoff is a German-based company that provides industrial automation control and information products worldwide, across a wide range of industries.

According to Beckhoff, TwinCAT is deployed across several sectors including general and special purpose machine building, manufacturing, building automation, oil and gas, water and wastewater, electric utilities, renewable energies, and others and is deployed worldwide.

Vulnerability Characterization

Vulnerability Overview

A read access violation can occur when a specially crafted packet is sent to Port 48899\UDP.

CVE-2011-3486 has been assigned to this vulnerability.1 A CVSS bse score of 5.0 has also been assigned.

Vulnerability Details


This vulnerability is remotely exploitable.

Existence of Exploit

Public exploits are known to target this vulnerability.


An attacker with a low skill level can create the denial-of-service.


Beckhoff has developed a patch to address this vulnerability. To obtain the patch and installation instructions, customers should contact Beckhoff at patch@beckhoff.com.

If the customer is unable to apply the patch, Beckhoff recommends that customers deploy a firewall and restrict traffic on the affected port (48899\UDP).

ICS-CERT encourages asset owners to take additional defensive measures to protect against this and other cybersecurity risks.

  • Minimize network exposure for all control system devices. Critical devices should not directly face the Internet.
  • Locate control system networks and remote devices behind firewalls, and isolate them from the business network.
  • When remote access is required, use secure methods such as Virtual Private Networks (VPNs), recognizing that VPN is only as secure as the connected devices

ICS-CERT reminds organizations to perform proper impact analysis and risk assessment prior to taking defensive measures.

The Control Systems Security Program (CSSP) also provides a section for control system security recommended practices on the CSSP web page. Several recommended practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies.

Organizations observing any suspected malicious activity should follow their established internal procedures and report their findings to ICS-CERT for tracking and correlation against other incidents.

  • 1http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2011-3486, website last accessed October 06, 2011.

Contact Information

For any questions related to this report, please contact the CISA at:

Email: CISAservicedesk@cisa.dhs.gov
Toll Free: 1-888-282-0870

For industrial control systems cybersecurity information:  https://us-cert.cisa.gov/ics 
or incident reporting:  https://us-cert.cisa.gov/report

CISA continuously strives to improve its products and services. You can help by choosing one of the links below to provide feedback about this product.

This product is provided subject to this Notification and this Privacy & Use policy.

Please share your thoughts.

We recently updated our anonymous product survey; we'd welcome your feedback.