CVE-2021-22699Network attack vector

Service interruption via crafted HTTP requests

Published May 26, 2021 · Updated Aug 3, 2024

Improper input validation in Schneider Electric Modicon M241/M251 firmware before 5.1.9.1 allows remote attackers to interrupt service over HTTP. Schneider Electric has not disclosed the affected HTTP handler, malformed field, or validation error that processes crafted requests incorrectly. Exploitation requires network access to the controller's HTTP service and causes denial of service, with no reported data disclosure or modification.

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 Schneider Electric Modicon M241/M251 firmware before 5.1.9.1 allows remote attackers to interrupt service over HTTP. Schneider Electric has not disclosed the affected HTTP handler, malformed field, or validation error that processes crafted requests incorrectly. Exploitation requires network access to the controller's HTTP service and causes denial of service, with no reported data disclosure or modification.

The record

CVE
CVE-2021-22699
Published
May 26, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-20, T0814
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 26, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.8NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:C

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-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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