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750 823 FirmwareOperating system · Wago

CVE-2021-34596

MEDIUM · 6.5 CVSS v3.1 Published 2021-10-26
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
71/100
Remediation priority · Elevated
Remotely reachable Zero-click

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
A crafted request may cause a read access to an uninitialized pointer in CODESYS V2 Runtime Toolkit 32 Bit full and PLCWinNT prior to versions V2.4.7.56, resulting in a denial-of-service condition.

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 · moderate confidence

A vulnerability in CODESYS V2 Runtime Toolkit 32 Bit full and PLCWinNT allows a remote attacker to send a specially crafted request that triggers a read from an uninitialized pointer. This memory access violation causes the application to crash, resulting in a denial-of-service condition.

MitigationUpdate CODESYS V2 Runtime Toolkit and PLCWinNT to version V2.4.7.56 or later to remediate this vulnerability. If immediate patching is not possible, network segmentation and filtering of unexpected/proprietary protocol requests may reduce exposure.

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
750 823 FirmwareOperating system
Affected:< fw10
750 829 FirmwareOperating system
Affected:< fw17
750 831 FirmwareOperating system
Affected:< fw17
750 832 FirmwareOperating system
Affected:< fw10
750 852 FirmwareOperating system
Affected:< fw17
750 862 FirmwareOperating system
Affected:< fw10
750 880 FirmwareOperating system
Affected:< fw17
750 881 FirmwareOperating system
Affected:< fw17

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
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/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 the Wago 750 model
    Check the device label, documentation, or query the PLC firmware information via the CODESYS development environment or the device's web interface if available
    Affected if The device is one of the following models: 750-823, 750-829, 750-831, 750-832, 750-852, 750-862, 750-880, or 750-881
  2. Check the installed firmware version
    Access the PLC via CODESYS, the device web interface, or use manufacturer-provided tools to retrieve the current firmware version
    Affected if The firmware version is below fw10 for models 750-823, 750-832, or 750-862; OR below fw17 for models 750-829, 750-831, 750-852, 750-880, or 750-881
  3. Confirm CODESYS V2 Runtime Toolkit is in use
    Verify that the PLC is running the CODESYS V2 Runtime Toolkit 32 Bit full version by checking the runtime information in the CODESYS development environment or device diagnostics
    Affected if The CODESYS V2 Runtime Toolkit 32 Bit full is installed and running on the device
  4. Check network exposure of the CODESYS runtime
    Review network configuration, firewall rules, and accessible ports to determine if the CODESYS runtime is reachable from network segments outside the local control system
    Affected if The PLC with vulnerable firmware is directly accessible on the network without proper segmentation or filtering

A user is affected if they are running any of the specified Wago 750 models with firmware versions below the thresholds and the CODESYS V2 Runtime Toolkit is network-accessible.

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
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Update CODESYS V2 Runtime Toolkit and PLCWinNT to version V2.4.7.56 or later to remediate this vulnerability. If immediate patching is not possible, network segmentation and filtering of unexpected/proprietary protocol requests may reduce exposure.

Recommended fix Moderate confidence

CODESYS V2 Runtime Toolkit V2.4.7.56 (or later) - corresponding firmware: fw10+ for 750 823/750 832/750 862, fw17+ for 750 829/750 831/750 852/750 880/750 881

  1. Identify the specific 750 controller model from the affected list (750 823, 750 829, 750 831, 750 832, 750 852, 750 862, 750 880, or 750 881)
  2. Locate the current firmware version running on the controller
  3. Download the firmware update from the official CODESYS/Codesys customer portal at customers.codesys.com
  4. Upgrade the controller firmware to version fw10 or higher for 750 823, 750 832, and 750 862 models
  5. Upgrade the controller firmware to version fw17 or higher for 750 829, 750 831, 750 852, 750 880, and 750 881 models
  6. Verify that the CODESYS V2 Runtime Toolkit included in the firmware is version V2.4.7.56 or later
  7. After upgrade, test that the device responds normally and the vulnerability is mitigated
Caveat Firmware upgrades on industrial controllers may require testing of control applications; ensure backup of current configuration before upgrading

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

Fix this in 750 823 Firmware Scoped from the published advisory
  • Consultation2.0 h
  • Implementation2.0 h
  • Testing4.0 h
  • Review / QA2.0 h
10.0 hours of engineering $1,720
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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-2021-34596 in production — separate from our analysis above.

No notes yet

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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