How severe is CVE-2021-20596?

CVE-2021-20596 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-20596 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (80th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-20596?

CVE-2021-20596 primarily affects Mitsubishielectric Fx3u-enet-l Firmware. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-20596?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-20596 published?

CVE-2021-20596 was published on 2021-07-22 and last updated on 2026-06-17.

CVE-2021-20596

CVE-2021-20596 is a high-severity vulnerability in Mitsubishielectric Fx3u-enet-l Firmware with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-476.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 2% (80th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-476
Affected product: Mitsubishielectric Fx3u-enet-l Firmware
Published: 2021-07-22
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-20596?: 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.
How severe is CVE-2021-20596?: CVE-2021-20596 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-20596 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (80th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-20596?: CVE-2021-20596 primarily affects Mitsubishielectric Fx3u-enet-l Firmware. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-20596?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-20596 published?: CVE-2021-20596 was published on 2021-07-22 and last updated on 2026-06-17.

References

Affected products (3)

cpe:2.3:o:mitsubishielectric:fx3u-enet-l_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:mitsubishielectric:fx3u-enet-p502_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:mitsubishielectric:fx3u-enet_firmware:*:*:*:*:*:*:*:*

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