HOMEVULNERABILITIESCVE-2021-20596
HIGH

CVE-2021-20596

CWE-476Published: July 22, 2021· Updated: Jun 17, 2026

7.5
CVSS v3.1

Official 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.

NVD Source

Technical Analysis

CVE-2021-20596 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 7.5.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityNone
IntegrityNone
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected Vendors & Products

mitsubishielectric3 product(s)
fx3u-enet-l firmwarefx3u-enet-p502 firmwarefx3u-enet firmware
Source: NVD CPE · 3 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

PATCHhttps://jvn.jp/vu/JVNVU94348759/index.html
PATCHhttps://www.mitsubishielectric.com/en/psirt/vulnerability/pdf/2021-006_en.pdf
PATCHhttps://jvn.jp/vu/JVNVU94348759/index.html
PATCHhttps://www.mitsubishielectric.com/en/psirt/vulnerability/pdf/2021-006_en.pdf
ADVISORYhttps://us-cert.cisa.gov/ics/advisories/icsa-21-201-01
ADVISORYhttps://us-cert.cisa.gov/ics/advisories/icsa-21-201-01

All References (6)

→
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

Quick Facts

CVE IDCVE-2021-20596
CVSS Score7.5 / 10
SeverityHIGH
WeaknessCWE-476
CISA KEVNo
Affected1 vendor(s)
PublishedJul 22, 2021

Related CVEs (CWE-476)

CVE-2022-36648
10.0
CVE-2010-2495
10.0
CVE-2018-14562
9.8
CVE-2023-46427
9.8
CVE-2024-47613
9.8
CVE-2022-0582
9.8

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-20596 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.
← All Vulnerabilities·Search for CVE-2021-20596·NVD