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Plcnext FirmwareOperating system · Phoenixcontact

CVE-2020-12517

CRITICAL · 9.0 CVSS v3.1 Published 2020-12-17
Fix available
A fix is available. Upgrade to 2021.0 or later.
See remediation →
94/100
Remediation priority · Urgent
Remotely reachable

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
On Phoenix Contact PLCnext Control Devices versions before 2021.0 LTS an authenticated low privileged user could embed malicious Javascript code to gain admin rights when the admin user visits the vulnerable website (local privilege escalation).

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

A stored Cross-Site Scripting (XSS) vulnerability in the Phoenix Contact PLCnext Control web interface allows an authenticated low-privileged user to inject malicious JavaScript that executes when an admin user views the affected page, enabling privilege escalation to admin rights.

MitigationUpgrade to PLCnext Control version 2021.0 LTS or later. If immediate upgrade is not possible, implement strict input validation and output encoding on all user-supplied fields, and consider restricting low-privileged user access to the web interface until the patch is applied.

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
Plcnext FirmwareOperating system
Affected:< 2021.0

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
Network
Complexity
Low
Privileges
Low
User interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/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. Identify PLCnext Control device on network
    Access the device web interface via its IP address (typically https://<device-ip>) and locate the firmware version in System Information or About section of the web UI
    Affected if Device is accessible and responds on web ports (80/443)
  2. Check installed firmware version
    In the web interface, navigate to System > Overview or Administration > System Info and locate the firmware version number
    Affected if Firmware version shown is earlier than 2021.0 (e.g., 2020.x, 2019.x, etc.)
  3. Verify web interface is enabled
    Check device network settings via SSH or the web UI to confirm the HTTP/HTTPS web server is running on ports 80/443
    Affected if Web interface is active and accepting connections
  4. Confirm low-privileged user accounts exist
    Navigate to User Administration or Users section in the web interface and list accounts with role-based access (non-admin users)
    Affected if Any user account with limited/operator role exists in addition to admin accounts
  5. Identify user-editable fields in web interface
    Navigate through web interface pages where users can submit content (project names, device descriptions, comments, etc.) and note where input fields accept user-supplied text
    Affected if Web interface contains input fields visible to other users or admins

The environment is affected if the PLCnext firmware version is below 2021.0 AND the web interface is accessible with multiple user roles present, allowing a low-privileged user to inject malicious script into a field that admins view.

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.

dbcve · scoped
Upgrade available Upgrade to 2021.0 or later
Fixed in 2021.0
Interim mitigation

Upgrade to PLCnext Control version 2021.0 LTS or later. If immediate upgrade is not possible, implement strict input validation and output encoding on all user-supplied fields, and consider restricting low-privileged user access to the web interface until the patch is applied.

Recommended fix High confidence

2021.0 LTS

  1. Back up the current PLCnext Control device configuration and project files
  2. Download the firmware version 2021.0 LTS from the official Phoenix Contact support website (cert.vde.com or phoenixcontact.com)
  3. Access the web-based management interface of the PLCnext device
  4. Navigate to the firmware update section in the administration settings
  5. Upload and install the 2021.0 LTS firmware file following the on-screen instructions
  6. Allow the device to reboot and complete the firmware update process
  7. Verify the upgrade was successful by checking the firmware version in the web interface
  8. Confirm the XSS vulnerability is resolved by logging in as both admin and low-privileged users
Caveat Firmware upgrades on industrial control devices may affect running applications; test in a staging environment before production deployment

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Plcnext Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA3.0 h
19.0 hours of engineering $3,380
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An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $5,408.

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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-2020-12517 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data