CVE-2021-33485Network attack vector

Remote code execution via crafted web requests

Published Aug 3, 2021 · Updated May 29, 2026

Heap-based buffer overflow in the CODESYS WebVisu web server before 3.5.17.10 allows remote attackers to execute code via crafted requests. The optional CmpWebServer component mishandles crafted web requests and writes beyond a heap buffer, although CODESYS has not disclosed the affected parser or field. The web server must be present and network-reachable; exploitation can crash it, interrupt the runtime, or execute code without authentication.

CVSS severity9.8
Critical
EPSS probability1.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap-based buffer overflow in the CODESYS WebVisu web server before 3.5.17.10 allows remote attackers to execute code via crafted requests. The optional CmpWebServer component mishandles crafted web requests and writes beyond a heap buffer, although CODESYS has not disclosed the affected parser or field. The web server must be present and network-reachable; exploitation can crash it, interrupt the runtime, or execute code without authentication.

The record

CVE
CVE-2021-33485
Published
Aug 3, 2021
Updated
May 29, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-122, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 3, 2021CVE publishedPublication date reported by the CVE source.
  2. May 29, 2026Record 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

9.8CODESYS GmbHCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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-122Heap-based Buffer Overflow
T1190Exploit Public-Facing Application

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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