CVE-2021-33541Network attack vector

Network communication outage via crafted IP packets

Published Jun 25, 2021 · Updated Sep 16, 2024

Resource exhaustion in all Phoenix Contact ILC1x0 and ILC1x1 variants allows remote attackers to stop network communication via crafted IP packets. The PLC network communication module allocates resources without limits or throttling while processing the packets, exhausting capacity needed for communications. No authentication is required; the automation task continues, but restoring network connectivity requires restarting the device.

CVSS severity7.5
High
EPSS probability1.49%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Resource exhaustion in all Phoenix Contact ILC1x0 and ILC1x1 variants allows remote attackers to stop network communication via crafted IP packets. The PLC network communication module allocates resources without limits or throttling while processing the packets, exhausting capacity needed for communications. No authentication is required; the automation task continues, but restoring network connectivity requires restarting the device.

The record

CVE
CVE-2021-33541
Published
Jun 25, 2021
Updated
Sep 16, 2024
Vendor
Phoenix Contact
Product
ILC 1xx
Classifications
CWE-770, T0814
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 25, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=ILC1x0 all variants
  2. Affected versionversion=ILC1x1 all variants

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Phoenix Contact · ILC 1xxversion=ILC1x0 all variants; version=ILC1x1 all variants

Published CVSS scores

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-770Allocation of Resources Without Limits or Throttling
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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo