CVE-2021-20596

Name: CVE-2021-20596
Creator: NVD / NIST
Published: 2021-07-22T12:15:07.787+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 7.5/10EPSS 2.17%

Last modified Jun 17, 2026

CVE-2021-20596 is a high-severity vulnerability rated 7.5/10 on the CVSS scale. NULL Pointer Dereference in MELSEC-F Series FX3U-ENET firmware version 1.14 and prior, FX3U-ENET-L firmware version 1.14 and prior and FX3U-ENET-P502 firmware version 1.14 and prior allows a remote unauthenticated attacker to cause a DoS condition in communication by sending specially crafted packets. Control by MELSEC-F series PLC is not affected and system reset is required for recovery.. EPSS estimates a 2.17% chance of exploitation in the next 30 days.

Description

NULL Pointer Dereference in MELSEC-F Series FX3U-ENET firmware version 1.14 and prior, FX3U-ENET-L firmware version 1.14 and prior and FX3U-ENET-P502 firmware version 1.14 and prior allows a remote unauthenticated attacker to cause a DoS condition in communication by sending specially crafted packets. Control by MELSEC-F series PLC is not affected and system reset is required for recovery.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

2.17%

80.0th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-476

Affected Software

Vendor	Product	Versions
Mitsubishielectric	Fx3u-Enet-L Firmware	<= 1.14
Mitsubishielectric	Fx3u-Enet-P502 Firmware	<= 1.14
Mitsubishielectric	Fx3u-Enet Firmware	<= 1.14

References

https://jvn.jp/vu/JVNVU94348759/index.htmlPatch, Third Party Advisory
https://us-cert.cisa.gov/ics/advisories/icsa-21-201-01Third Party Advisory
https://www.mitsubishielectric.com/en/psirt/vulnerability/pdf/2021-006_en.pdfPatch, Vendor Advisory
https://jvn.jp/vu/JVNVU94348759/index.htmlPatch, Third Party Advisory
https://us-cert.cisa.gov/ics/advisories/icsa-21-201-01Third Party Advisory
https://www.mitsubishielectric.com/en/psirt/vulnerability/pdf/2021-006_en.pdfPatch, Vendor Advisory

Timeline

Published: Jul 22, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-20596?

How severe is CVE-2021-20596?

CVE-2021-20596 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 2.17% probability of exploitation in the next 30 days.

How do I fix CVE-2021-20596?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-20596?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST