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Twincat Extended Automation RuntimeApplication · Beckhoff

CVE-2020-12510

HIGH · 7.3 CVSS v3.1 Published 2020-11-19
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
73/100
Remediation priority · Elevated

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
The default installation path of the TwinCAT XAR 3.1 software in all versions is underneath C:\TwinCAT. If the directory does not exist it and further subdirectories are created with permissions which allow every local user to modify the content. The default installation registers TcSysUI.exe for automatic execution upon log in of a user. If a less privileged user has a local account he or she can replace TcSysUI.exe. It will be executed automatically by another user during login. This is also true for users with administrative access. Consequently, a less privileged user can trick a higher privileged user into executing code he or she modified this way. By default Beckhoff’s IPCs are shipped with TwinCAT software installed this way and with just a single local user configured. Thus the vulnerability exists if further less privileged users have been added.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

The TwinCAT XAR 3.1 installer creates the C:\TwinCAT directory with overly permissive access controls allowing all local users to modify contents. The TcSysUI.exe auto-start executable can be replaced by a less privileged user, enabling code execution with the privileges of any subsequent user who logs in.

MitigationRestrict directory permissions on C:\TwinCAT to administrators only and disable or secure the TcSysUI.exe auto-start entry to prevent unauthorized modification by non-privileged users.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Twincat Extended Automation RuntimeApplication
Affected:= 3.1

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
Required
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Verify TwinCAT XAR 3.1 installation
    Check if Beckhoff TwinCAT Extended Automation Runtime version 3.1 is installed on the system by reviewing installed programs in Control Panel or using: Get-ItemProperty HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\* | Where-Object {$_.DisplayName -like '*TwinCAT*'}
    Affected if TwinCAT XAR 3.1 is installed and the directory C:\TwinCAT exists on the system
  2. Confirm C:\TwinCAT directory exists
    Verify that the C:\TwinCAT directory exists on the system by running: Test-Path C:\TwinCAT
    Affected if The C:\TwinCAT directory exists on the system
  3. Inspect access control permissions on C:\TwinCAT
    Check the permissions on the C:\TwinCAT directory using: Get-Acl C:\TwinCAT | Select-Object -ExpandProperty Access | Format-Table -AutoSize. Look for entries granting Write or Modify permissions to the Users group or Everyone.
    Affected if The permissions allow non-administrative users (such as Users group or Everyone) to Write or Modify files in C:\TwinCAT
  4. Locate TcSysUI.exe auto-start executable
    Find the TcSysUI.exe file by running: Get-ChildItem C:\TwinCAT -Recurse -Filter TcSysUI.exe -ErrorAction SilentlyContinue. Also check auto-start locations in the registry: HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
    Affected if The TcSysUI.exe file exists in the C:\TwinCAT directory or is configured to auto-start
  5. Verify write access to TcSysUI.exe for standard users
    Attempt to verify if a standard (non-privileged) user account can modify or replace the TcSysUI.exe file. This can be done by reviewing the file permissions on the executable itself using: Get-Acl C:\TwinCAT\*\TcSysUI.exe | Select-Object -ExpandProperty Access
    Affected if Standard users have Write or Modify permissions to the TcSysUI.exe file, allowing them to replace it with a malicious executable

A user is affected if TwinCAT XAR 3.1 is installed with the C:\TwinCAT directory having overly permissive access controls that allow standard users to modify the TcSysUI.exe auto-start executable.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Restrict directory permissions on C:\TwinCAT to administrators only and disable or secure the TcSysUI.exe auto-start entry to prevent unauthorized modification by non-privileged users.

Fix this in Twincat Extended Automation Runtime Scoped from the published advisory
  • Consultation2.0 h
  • Implementation3.0 h
  • Testing2.0 h
  • Review / QA1.0 h
8.0 hours of engineering $1,420
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2020-12510 in production — separate from our analysis above.

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What this is

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What belongs here
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