CVE-2021-34584Public exploitNetwork attack vector

Memory disclosure or crash via oversized copy

Published Oct 26, 2021 · Updated Sep 16, 2024

Buffer over-read in CODESYS GmbH's V2 web server in Development System V2.3 allows remote attackers to disclose memory or cause a crash. The request handler copies an attacker-controlled byte count from a 256-byte stack buffer into a heap communication buffer without limiting the count to the available buffer sizes. Versions before 1.1.9.20 remain exposed despite user management; versions 1.1.9.20 and 1.1.9.21 process the request when WebVisu user management is disabled or after authentication.

CVSS severity9.1
Critical
EPSS probability1.11%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Buffer over-read in CODESYS GmbH's V2 web server in Development System V2.3 allows remote attackers to disclose memory or cause a crash. The request handler copies an attacker-controlled byte count from a 256-byte stack buffer into a heap communication buffer without limiting the count to the available buffer sizes. Versions before 1.1.9.20 remain exposed despite user management; versions 1.1.9.20 and 1.1.9.21 process the request when WebVisu user management is disabled or after authentication.

The record

CVE
CVE-2021-34584
Published
Oct 26, 2021
Updated
Sep 16, 2024
Vendor
CODESYS GmbH
Product
CODESYS Development System V2.3
Classifications
CWE-126, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 26, 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=all web servers <V1.1.9.22

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

CODESYS GmbH · CODESYS Development System V2.3version=all web servers <V1.1.9.22

Published CVSS scores

6.4NVDAV:N/AC:L/Au:N/C:P/I:N/A:P
9.1CODESYS GmbHCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/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 exploitPublished

Weakness, pattern, technique

CWE-126Buffer Over-read
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

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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