CVE-2021-20596

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of service disruption.

Exploit odds

2.2% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-07-22 12:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:34 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 2.2% in the next 30 days (EPSS).
• Severity: 7.5 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-07-22 12:15 UTC

Last modified

2026-06-17 03:34 UTC

Exploit probability

2.2% · EPSS, next 30 days

Weakness

CWE-476 · NULL pointer dereference

Record status

Modified

Affected

• Mitsubishielectric fx3u-enet-l Firmware ≤ 1.14
• Mitsubishielectric fx3u-enet-p502 Firmware ≤ 1.14
• Mitsubishielectric fx3u-enet Firmware ≤ 1.14

Attack profile CVSS 3.1 · 7.5

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-20596.md and follow it. Check whether this project is affected by CVE-2021-20596. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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