No exploitation reportedFix available

CVE-2021-20596

No exploitation reported by the sources we read.

Published2021-07-22
WeaknessCWE-476

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

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.

Timeline

dates in UTC

2021-07-2212:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-20596?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-20596?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Mitsubishielectric fx3u-enet firmware

Branch	Affected	Fixed in	Source
1.14	≤ 1.14	no fix published	NVD

Mitsubishielectric fx3u-enet-l firmware

Branch	Affected	Fixed in	Source
1.14	≤ 1.14	no fix published	NVD

Mitsubishielectric fx3u-enet-p502 firmware

Branch	Affected	Fixed in	Source
1.14	≤ 1.14	no fix published	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

ICSA-21-201-01 CISA3 known affected
Mitsubishi Electric MELSEC-F Series
FX3U-ENET-P502: Firmware Version 1.14 and prior · FX3U-ENET-L: Firmware Version 1.14 and prior · FX3U-ENET: Firmware Version 1.14 and prior

Full record on NVD

Fix

Vendor fix CISA ICSA-21-201-01 · 3 productsFX3U-ENET: Firmware Version 1.16 or later
Vendor fix CISA ICSA-21-201-01 · 3 productsFX3U-ENET-L: Firmware Version 1.16 or later
Vendor fix CISA ICSA-21-201-01 · 3 productsFX3U-ENET-P502: Firmware Version 1.16 or later
Mitigation from the vendor CISA ICSA-21-201-01 · 3 productsUse a firewall or virtual private network (VPN), etc., to prevent unauthorized access when Internet access is required.
Mitigation from the vendor CISA ICSA-21-201-01 · 3 productsUse within a LAN and block access from untrusted networks and hosts through firewalls.
Mitigation from the vendor CISA ICSA-21-201-01 · 3 productsPlease refer to the Mitsubishi Electric advisory for further details.

Advisories and patches

jvn.jpPatch
www.mitsubishielectric.comPatch · Vendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

NVDCVSS 3.17.5read 2026-10-23
NVDCVSS 2.05read 2026-10-23
NVDweakness (CWE)CWE-476read 2026-10-23
FIRST EPSSEPSS score2.2 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: 2021-07-22
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-20596?

Is CVE-2021-20596 actively exploited?

Active exploitation of CVE-2021-20596 has not been confirmed. Its EPSS score was 2.2% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-20596?

CVE-2021-20596 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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