CVE-2021-34570Network attack vector

Controller restart via malformed access-token JSON request

Published Sep 27, 2021 · Updated Sep 16, 2024

Improper input validation in Phoenix Contact PLCnext Technology before 2021.0.5 LTS allows remote attackers to restart controllers. The /auth/access-token endpoint mishandles a specially crafted JSON request and restarts the controller instead of rejecting malformed input. The endpoint is reachable without authentication from the controller's network, and repeated requests can sustain a service interruption.

CVSS severity7.5
High
EPSS probability0.98%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in Phoenix Contact PLCnext Technology before 2021.0.5 LTS allows remote attackers to restart controllers. The /auth/access-token endpoint mishandles a specially crafted JSON request and restarts the controller instead of rejecting malformed input. The endpoint is reachable without authentication from the controller's network, and repeated requests can sustain a service interruption.

The record

CVE
CVE-2021-34570
Published
Sep 27, 2021
Updated
Sep 16, 2024
Vendor
Phoenix Contact
Product
PLCnext Technology
Classifications
CWE-20, T0814
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 27, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=PLCnext Technology Starterkit (1188165) <2021.0.5 LTS

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Phoenix Contact · PLCnext Technologyversion=PLCnext Technology Starterkit (1188165) <2021.0.5 LTS

Published CVSS scores

7.8NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:C
9.1Phoenix ContactCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
7.5CERT VDECVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T0814Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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