A CWE-334: Small Space of Random Values vulnerability exists in Modicon M221 (all references, all versions) that could allow the attacker t…

published 2020-11-19 5 y ago modified 2026-06-17 4 mo ago also EUVD-2020-28691

cvss: 7.1; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 22%
public exploits: 0; none known

A CWE-334: Small Space of Random Values vulnerability exists in Modicon M221 (all references, all versions) that could allow the attacker to break the encryption keys when the attacker has captured the traffic between EcoStruxure Machine - Basic software and Modicon M221 controller.

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

cisa ICSA-20-343-04 updated 2020-12-08 cvss 7.1

Schneider Electric Modicon M221 Programmable Logic Controller

Schneider Electric Software, LLC Modicon M221
affected: vendor fix, mitigation “Set up network segmentation and implement a firewall to block all unauthorized access to Port 502/TCP.” se.com

From CISA ICS and IT advisories (CSAF, https://github.com/cisagov/CSAF), a U.S. Government work; changed: reduced to products, statuses and remediations. CISA notification · csaf

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: total
Assessed: 5 mo ago (2026-05-29)

Exploit prediction

0.29% chance of exploitation in the next 30 days, higher than 22% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CISA ADP	3.1	7.1	CVSS:3.1/AV:A/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
NVD	3.1	7.3	CVSS:3.1/AV:A/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
CNA	3.1	7.1	CVSS:3.1/AV:A/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H
NVD	2.0	4.3	AV:A/AC:M/Au:N/C:P/I:P/A:N

Affected products

n/a Modicon M221, all references, all versions

Classification

Weakness

CWE-334 Small Space of Random Values

References

se.com /ww/en/download/document/SEVD-2020-315-05/
vendor-advisory
us-cert.cisa.gov /ics/advisories/icsa-20-343-04
third-party-advisory, us-government-resource

Sources

CVE List CVE-2020-7566
NVD CVE-2020-7566

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary